Re: [AMRadio] antenna tuners
> I don't believe in them. > > If you can't resonate your antenna, then what are you doing? You ar etransmitting some energy and you are getting a whole lot of reflected power that is wasted. You might also be cutting back a lot of your power in the final RF amplifier of a modern rig. > If you use a tuner, you are creating a voltage divider effect that > creates a reactive load in your shack, to ground that makes your antenna > "feed line + radiating elements". Maybe - what if the tuner is outside at the base of the antenna? > Over the years, the importance of having at least a 2:1 match with at > least 1.5:1 some where in the the antenna design. Huh? Over the years many of us have transmitted with a 3:1 SWR and no tuner and made plenty of contacts - tube finals of course! > Proper antenna design for your favorite frequencies is the best choice. But some of us can't always get what we want. When you MUST compromise, there is a LOT of good that can be said about a matching network for one's antenna. It is usually an impedance transformer rather than a "voltage divider." > I currently use a multi-element dipole to cover 80,40,20,15 and 10 meters. > Just like microphones in the sound work I help out with at church. If > they are not singing into the mic, I cannot "fix it" without creating a > gain structure that is sucking up to feed back" Different entirely from an antenna tuner. > You need to fix your problems at the source. The antenna is the load. > I our cases, it is resonance of your antenna, by some means. > > Even my hamstick on my jeep I have had GREAT success RESONATING antennas with a matching network. I don't understand why anyone would "not believe in" something when they are so effective.
Re: [AMRadio] antenna tuners
Thank you Brian for your correction. Of course we need to achieve resonance for the antennas of solid state rigs. And yes they are matching networks, however they do consume power that is wasted, especially at the end of a coax. However, they can be used at the feed point to much better effect. I do honestly believe in using resonant antennas. Also, I did not take into consideration the fellows using open wire feed lines to baluns inside the antenna tuner. I stand corrected. However, I will always try to achieve resonance in my antennas as that is the best way in my mind to radiate the most signal. I agree with you that there are some of us who have to resort to tuners for space reasons or other confinements. Thanks for assisting me in getting a clearer point across to the group. Yes, I do see the need for a matching transformer in some situations. I am currently running a tube station, so it can take SWR, but I wish to strive for the best match. And yes, the antenna tuner is a matching network consisting of coils and capacitors. Perhaps I chose the wrong analogy. You have provided me with stuff to read up on in order to remind myself of lessons learned long ago. Thank you. Best 73, Alan Brian Carling wrote: I don't believe in them. If you can't resonate your antenna, then what are you doing? You ar etransmitting some energy and you are getting a whole lot of reflected power that is wasted. You might also be cutting back a lot of your power in the final RF amplifier of a modern rig. If you use a tuner, you are creating a voltage divider effect that creates a reactive load in your shack, to ground that makes your antenna "feed line + radiating elements". Maybe - what if the tuner is outside at the base of the antenna? Over the years, the importance of having at least a 2:1 match with at least 1.5:1 some where in the the antenna design. Huh? Over the years many of us have transmitted with a 3:1 SWR and no tuner and made plenty of contacts - tube finals of course! Proper antenna design for your favorite frequencies is the best choice. But some of us can't always get what we want. When you MUST compromise, there is a LOT of good that can be said about a matching network for one's antenna. It is usually an impedance transformer rather than a "voltage divider." I currently use a multi-element dipole to cover 80,40,20,15 and 10 meters. Just like microphones in the sound work I help out with at church. If they are not singing into the mic, I cannot "fix it" without creating a gain structure that is sucking up to feed back" Different entirely from an antenna tuner. You need to fix your problems at the source. The antenna is the load. I our cases, it is resonance of your antenna, by some means. Even my hamstick on my jeep I have had GREAT success RESONATING antennas with a matching network. I don't understand why anyone would "not believe in" something when they are so effective. __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
Re: [AMRadio] antenna tuners
Allan, Had it not been for "Couplers" over the last 25 yrs, I would have been limited to operating possibly no more than 2 frequencies. I built a Center Fed Zepp as my first antenna, because a very wise OLD ham told me to build it and use it with a Coupler and I have been using that antenna all over the USA and twice in Canada! Same Antenna! Today I have a 160m Loop up 75' in the air also fed with 440 ohm ladder line and that has to be the very best antenna I have had the pleasure to use, It is Matched with a Palstar 5K coupler and it has worked well anywhere from 160m to 10m and all in between. I have simply had great success and been able to work multiple bands using Matching networks, Couplers, Tuners if you will. I honestly would NOT be without one in my shack. Tony/W5OD River House Radio At 04:45 AM 4/20/2006, you wrote: I don't believe in them. If you can't resonate your antenna, then what are you doing? If you use a tuner, you are creating a voltage divider effect that creates a reactive load in your shack, to ground that makes your antenna "feed line + radiating elements". Over the years, the importance of having at least a 2:1 match with at least 1.5:1 some where in the the antenna design. Proper antenna design for your favorite frequencies is the best choice. I currently use a multi-element dipole to cover 80,40,20,15 and 10 meters. I just use a VSWR bridge and back off the power when the SWR rises close to 2:1. I am not saying my answer is the best, I am only stating my opinion. Just like microphones in the sound work I help out with at church. If they are not singing into the mic, I cannot "fix it" without creating a gain structure that is sucking up to feed back" You need to fix your problems at the source. I our cases, it is resonance of your antenna, by some means. Even my hamstick on my jeep does great due to attention to resonance. 73 Alan VY2WU __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
Re: [AMRadio] antenna tuners
Hi all, Resonance Commercially, antennas are built for the task and pattern, match follows. If you think about it, one cannot obtain resonance of a straight dipole at every frequency in 75-80 meters (or 10 meters for that matter). By the equations (there are 3 definitions of resonance by the way) only one frequency can be "at resonance". So even on 75 while you may cut an antenna say for 3880, it is no longer "resonant" at 3510. Without getting into the calculus and Maxwell's equations, the radiation from an antenna is determined by integrating the incremental current along the wire or conductor. That and only that determines radiation. Matching is used to reduce losses in the feed system and or the final tank and to provide a symmetrical load to the final amplifier. By symmetrical, I mean the R is matching the plate Z (or xistor Z) and the x varies smoothly + and - around zero as the frequency is changed from low to high though the channel of interest. There are many AM broadcast stations of 50 kW that use a 5/8 wave radiator with a suitable matching network. This antenna is not resonant by definition but nevertheless radiates quite well and has a gain over a 1/4 wave resonant antenna working against a 1/4 wave ground system. A single frequency T network is used to bring the input Z to 50J0 at the "doghouse" at the base of the tower. A properly designed network will have a loss of only a few percent which is insignificant. (In Broadcast AM directionals, the FCC "allows" 8 percent loss for ALL the networks, i.e. the phasor/power divider and each of the tower networks. 8% in power is 0.36 dB!). The only real "problem" and it probably isn't a problem is standing waves on the feedline will also radiate distorting the "pattern" but most HF antennas are way too close to the ground anyway and that really distorts the pattern and greatly increases ground losses. Many years ago in QST there was an article by an engineer from I think RCA showing that losses in feed systems at HF are insignificant. From my Sig Corp texts and others, there are in fact ground losses associated with any feed system especially if the area below the feeders does not have a ground screen of some sort and the balance is not perfect. However, these losses are insignificant unless the feedline is very long. The problem with the typical SWR meter is you can't tell what you have at a dip. The X component polarity cannot be determined so you are working in the dark. The dip may be Z with the wrong value of R combining in quadrature with the X to give a Z of 50 ohms but not an R of 50 ohms. Only a good RF Z meter that displays X and R accurately can tell you what is really going on. They just don't exist for balanced lines. If you can truly float the bridge and RF source and detector you may be able to measure a balanced line at least at the lower bands. I have RF ammeters in both feeders so I know that at least I am in balance. So don't worry about resonance but do worry about baluns with reactive loads and poorly designed tuners that have high circulating currents within causing the losses we worry about AND get the wire up as high as possible unless you are working NVIS. Larry W3LW At 09:06 AM 4/20/2006, you wrote: Thank you Brian for your correction. Of course we need to achieve resonance for the antennas of solid state rigs. And yes they are matching networks, however they do consume power that is wasted, especially at the end of a coax. However, they can be used at the feed point to much better effect. I do honestly believe in using resonant antennas. Also, I did not take into consideration the fellows using open wire feed lines to baluns inside the antenna tuner. I stand corrected. However, I will always try to achieve resonance in my antennas as that is the best way in my mind to radiate the most signal. I agree with you that there are some of us who have to resort to tuners for space reasons or other confinements. Thanks for assisting me in getting a clearer point across to the group. Yes, I do see the need for a matching transformer in some situations. I am currently running a tube station, so it can take SWR, but I wish to strive for the best match. And yes, the antenna tuner is a matching network consisting of coils and capacitors. Perhaps I chose the wrong analogy. You have provided me with stuff to read up on in order to remind myself of lessons learned long ago. Thank you. Best 73, Alan Brian Carling wrote: I don't believe in them. If you can't resonate your antenna, then what are you doing? You ar etransmitting some energy and you are getting a whole lot of reflected power that is wasted. You might also be cutting back a lot of your power in the final RF amplifier of a modern rig. If you use a tuner, you are creating a voltage divider effect that creates a reactive load in your shack, to ground that makes y
RE: [AMRadio] antenna tuners
Hi Alan, No need to go away! You will get lots of good info here and asking / discussing is how to understand. As to resonant antennas, it makes no difference in how well they radiate. Resonance of the antenna is not required. SWR is not all that bad either as long as the transmitter sees a match, especially the solid state rigs. When open wire feed line is used there is usually very high SWR on the feed line. If you connect 450 ohm line to a half wave dipole which is normally in the 50 to 70 ohm range you have high swr on the feed line. And no, high swr on a feed line will not cause it to radiate. What causes feed line radiation is an unbalance between the two wires in the feed line. High SWR on coax line will cause a little more loss in the feed line due to the higher currents involved across the lower impedance of the coax. That is why when using open wire line that is 400 to 600 ohms, there is much less loss. The same power across a higher impedance means less current and less current going through the feed line wire means less power loss. An antenna tuner just matches the impedance seen at the transmitter end of the feed line to the 50 ohm transmitter output. If there is high swr on the feed line, any power reflected from the antenna is not wasted it is just re-reflected back to the antenna and eventually gets radiated. At HF even fairly high swr on coax lines does not cause excessive loss. 73 Gary K4FMX > -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Alan Beck > Sent: Thursday, April 20, 2006 5:45 AM > To: AMRadio@mailman.qth.net > Subject: [AMRadio] antenna tuners > > I don't believe in them. > > If you can't resonate your antenna, then what are you doing? > > If you use a tuner, you are creating a voltage divider effect that > creates a reactive load in your shack, to ground that makes your antenna > "feed line + radiating elements". > > Over the years, the importance of having at least a 2:1 match with at > least 1.5:1 some where in the the antenna design. > > Proper antenna design for your favorite frequencies is the best choice. > > I currently use a multi-element dipole to cover 80,40,20,15 and 10 meters. > > I just use a VSWR bridge and back off the power when the SWR rises close > to 2:1. > > I am not saying my answer is the best, I am only stating my opinion. > > Just like microphones in the sound work I help out with at church. If > they are not singing into the mic, I cannot "fix it" without creating a > gain structure that is sucking up to feed back" > > You need to fix your problems at the source. > > I our cases, it is resonance of your antenna, by some means. > > Even my hamstick on my jeep does great due to attention to resonance. > > 73 > Alan > VY2WU > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
RE: [AMRadio] antenna tuners
I was thinking of putting an add-on kit on my vertical to make it resonant on six meters, but now I'm thinking that might be a waste of time and money if I can tune the antenna on that band with my tuner and get a low swr at the transceiver. It's a tube rig, so it probably doesn't need a real low swr anyway. Any thoughts or recommendations? Thanks, Al, WA2AS -Original Message- From: Gary Schafer [mailto:[EMAIL PROTECTED] Sent: Thursday, April 20, 2006 11:08 AM To: 'Discussion of AM Radio' Subject: RE: [AMRadio] antenna tuners Hi Alan, No need to go away! You will get lots of good info here and asking / discussing is how to understand. As to resonant antennas, it makes no difference in how well they radiate. Resonance of the antenna is not required. SWR is not all that bad either as long as the transmitter sees a match, especially the solid state rigs. When open wire feed line is used there is usually very high SWR on the feed line. If you connect 450 ohm line to a half wave dipole which is normally in the 50 to 70 ohm range you have high swr on the feed line. And no, high swr on a feed line will not cause it to radiate. What causes feed line radiation is an unbalance between the two wires in the feed line. High SWR on coax line will cause a little more loss in the feed line due to the higher currents involved across the lower impedance of the coax. That is why when using open wire line that is 400 to 600 ohms, there is much less loss. The same power across a higher impedance means less current and less current going through the feed line wire means less power loss. An antenna tuner just matches the impedance seen at the transmitter end of the feed line to the 50 ohm transmitter output. If there is high swr on the feed line, any power reflected from the antenna is not wasted it is just re-reflected back to the antenna and eventually gets radiated. At HF even fairly high swr on coax lines does not cause excessive loss. 73 Gary K4FMX > -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Alan Beck > Sent: Thursday, April 20, 2006 5:45 AM > To: AMRadio@mailman.qth.net > Subject: [AMRadio] antenna tuners > > I don't believe in them. > > If you can't resonate your antenna, then what are you doing? > > If you use a tuner, you are creating a voltage divider effect that > creates a reactive load in your shack, to ground that makes your antenna > "feed line + radiating elements". > > Over the years, the importance of having at least a 2:1 match with at > least 1.5:1 some where in the the antenna design. > > Proper antenna design for your favorite frequencies is the best choice. > > I currently use a multi-element dipole to cover 80,40,20,15 and 10 meters. > > I just use a VSWR bridge and back off the power when the SWR rises close > to 2:1. > > I am not saying my answer is the best, I am only stating my opinion. > > Just like microphones in the sound work I help out with at church. If > they are not singing into the mic, I cannot "fix it" without creating a > gain structure that is sucking up to feed back" > > You need to fix your problems at the source. > > I our cases, it is resonance of your antenna, by some means. > > Even my hamstick on my jeep does great due to attention to resonance. > > 73 > Alan > VY2WU > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb The information contained in this message is confidential and intended only for use of the designated recipient(s) named above. If the reader of this message is not the intended recipient or an agent responsible for delivering it to the intended recipient, you are hereby notified that you have received this message in error, and that any review, dissemination, distribution, copying, or alteration of this message is strictly prohibited. If you have received this communication in error, please notify the originator immediately and remove it from your system.
RE: [AMRadio] antenna tuners
SWR is not all that bad either as long as the transmitter sees a match, especially the solid state rigs...And no, high swr on a feed line will not cause it to radiate. What causes feed line radiation is an unbalance between the two wires in the feed line. High SWR on coax line will cause a little more loss in the feed line due to the higher currents involved across the lower impedance of the coax. That is why when using open wire line that is 400 to 600 ohms, there is much less loss. The same power across a higher impedance means less current and less current going through the feed line wire means less power loss. Another factor causing loss with a high SWR is dielectric losses at the recurring high rf voltage points along the line. At low impedances, it is the resistive loss in the wire, and at high impedances, it is dielectric losses that combine to cause signal loss. But SWR is much, much less critical than most hams have been led to believe. An antenna tuner just matches the impedance seen at the transmitter end of the feed line to the 50 ohm transmitter output. If there is high swr on the feed line, any power reflected from the antenna is not wasted it is just re-reflected back to the antenna and eventually gets radiated. At HF even fairly high swr on coax lines does not cause excessive loss. My 160m. vertical uses a 140' run of buried RG-213 from the shack to the antenna tuner at the base of the tower. I set the L-network to match the tower 1:1 SWR at 1900 kc and locked it down. The SWR is about 2.5:1 at 1800 kc and the same at 2000 kc. I have measured the rf power input to the tower using a General Radio antenna impedance bridge and thermocouple rf ammeter, and at the same DC input power to the final amplifier, I could not detect any significant difference in rf power at the antenna end of the feedline, across the entire band. Of course at each point I had to re-measure the base impedance of the tower, note the rf ammeter readings, and re-calculate per ohm's law, so I do not guarantee precision measurements, but the ballpark power was consistent across the band, with no evidence of excessive loss at the top and bottom edges Don k4kyv.
RE: [AMRadio] antenna tuners
> > Another factor causing loss with a high SWR is dielectric losses at the > recurring high rf voltage points along the line. At low impedances, it is > the resistive loss in the wire, and at high impedances, it is dielectric > losses that combine to cause signal loss. But SWR is much, much less > critical than most hams have been led to believe. It is my understanding that at HF only resistive loss comes into play. Dielectric loss isn't a problem until you get into vhf. 73 Gary K4FMX
RE: [AMRadio] antenna tuners
Don & All, I'm about to dig a trench in my yard to run some coax and control cables to the back, in the bushes, our of harms (XYL eyesight) way. I'm curious... 1. Did you direct-bry the coax? I've had people tell me to go ahead and bury it. They say that by the time the coax deteriorates I should have replaced it anyway. On the other hand, you can buy poly hose pretty cheap. That would keep the lines dry and protect them from an errant shovel or two. 2. How bad is it to run various lines together in a tube. Would I be better off to run them at least a few inches part to minimize inductive pickup? 3. Of course it would need to be separate but: Has anyone run ladderline underground? Theoretically it's possible but my intuition says "Don't do it!" 73, Mark W1EOF > -Original Message- > From: Donald Chester [mailto:[EMAIL PROTECTED] > Sent: Thursday, April 20, 2006 12:58 PM > To: amradio@mailman.qth.net > Subject: RE: [AMRadio] antenna tuners > > > > > >SWR is not all that bad either as long as the transmitter sees a match, > >especially the solid state rigs...And no, high swr > >on a feed line will not cause it to radiate. > >What causes feed line radiation is an unbalance between the two wires in > >the > >feed line. > > >High SWR on coax line will cause a little more loss in the feed > line due to > >the higher currents involved across the lower impedance of the > coax. That > >is > >why when using open wire line that is 400 to 600 ohms, there is much less > >loss. The same power across a higher impedance means less > current and less > >current going through the feed line wire means less power loss. > > Another factor causing loss with a high SWR is dielectric losses at the > recurring high rf voltage points along the line. At low > impedances, it is > the resistive loss in the wire, and at high impedances, it is dielectric > losses that combine to cause signal loss. But SWR is much, much less > critical than most hams have been led to believe. > > > > >An antenna tuner just matches the impedance seen at the > transmitter end of > >the feed line to the 50 ohm transmitter output. If there is high > swr on the > >feed line, any power reflected from the antenna is not wasted it is just > >re-reflected back to the antenna and eventually gets radiated. > > > >At HF even fairly high swr on coax lines does not cause excessive loss. > > My 160m. vertical uses a 140' run of buried RG-213 from the shack to the > antenna tuner at the base of the tower. I set the L-network to > match the > tower 1:1 SWR at 1900 kc and locked it down. The SWR is about > 2.5:1 at 1800 > kc and the same at 2000 kc. I have measured the rf power input > to the tower > using a General Radio antenna impedance bridge and thermocouple > rf ammeter, > and at the same DC input power to the final amplifier, I could not detect > any significant difference in rf power at the antenna end of the > feedline, > across the entire band. Of course at each point I had to re-measure the > base impedance of the tower, note the rf ammeter readings, and > re-calculate > per ohm's law, so I do not guarantee precision measurements, but the > ballpark power was consistent across the band, with no evidence > of excessive > loss at the top and bottom edges > > Don k4kyv. > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.385 / Virus Database: 268.4.4/319 - Release Date: 4/19/06 > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.4.4/319 - Release Date: 4/19/06
RE: [AMRadio] antenna tuners
There should be no problem with running coax under ground directly buried or inside some other conduit including metal and run as many as you want side-by-side. Balanced line is another thing. Any transmission line will give you trouble if the characteristics of the insulation is not constant throughout the length of the line. In the case of balanced line the electromagnetic fields will be most intense between the lines but will also surround the lines so that any discontinuity in the surrounding material will most defiantly cause the characteristics of the line to change and some materials are very susceptible to absorption of RF energy even though they are insulators to DC. Obviously conductive metals near the line or a real no-no. I would guess that open wire balanced lines even if made with insulation around it and buried underground would cause ground heating and a lot of RF loss as opposed to hanging nicely from a doublet to a tuner is nearly with out loss. I once had a 75 meter doublet (120 ft) center fed with coax and changed it to the 60 ft of open wire down line. The antenna center was supported by a 50 ft pushup pole on the top of the house. The 60 feet of open wire down line would just reach to the edge of the roof and under the roof edge where the balanced tuner was mounted. It tuned perfectly but after about 3 minutes it would need to be retuned after about the 3rd time I found that the #12 wires of the open line were melting into the composition roof at the edge of the roof where the wires touched the roofing material. By the way, the wires had the regular plastic insulation on them that regular electric wires have. They were dielectric heating the composition roof material and melting down into it. I fastened a piece of Plexiglas to the roof so it would stick out from under the roofing material and cut notches in it for the wires to drop into and this solved the problem. I did an experiment once with a dummy load placed at the other end of the back yard. The dummy load had a self contained RF voltmeter on it. I ran 100 ft of brand new RG 8 to it from the connection of my SWR Bridge and loaded the rig to 2500 Volts at 400 ma on 3885 KHZ. The RF voltmeter said 185 VRMS at the 50 ohm load. The SWR Bridge sensitivity was up all the way and showed no reflected VSWR. I then ran 60 ft of open wire line from a Johnson KW match BOX to the 50 ohm (in place of the 100 ft of coax) and connected a 10 FT coax line from the VSWR bridge to the Match BOX. I adjusted the MATCH BOX until the VSWR reflected was zero with the sensitively up all the way. The rig tuned exactly the same as before and all meters measured the same except the RF voltmeter measured 195 Volts RMS across the 50 Ohm dummy load. So I would say that proves that 60 ft of open wire line and a Johnson KW MATCHBOX has less loss than 100 Ft of RG 8 at 3.885 MHz. During the same experimenting I found that the MATCHBOX did not like to be connected to the 50 ohm load directly using the balanced line output terminals on 3.885 MHZ. The impedance was to low for 75 meters. When connected to 45 to 75 ft of open wire line and the other end to the dummy load it would tune nicely on the 75 meter band and was very efficient. It did not like going over 80 ft on 75 meters of line and started acting as it did before when it was connected to the dummy load directly. It would probably start tuning right again if I had increased the line length to about 180 ft +/- 20 ft but I ran out of backyard as you need to suspend the line in a fairly straight line to make these tests or I would have had to stick poles in ground to hold up the line as I made turns around the yard. Great Discussions, John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of W1EOF Sent: Thursday, April 20, 2006 2:51 PM To: Discussion of AM Radio Subject: RE: [AMRadio] antenna tuners Don & All, I'm about to dig a trench in my yard to run some coax and control cables to the back, in the bushes, our of harms (XYL eyesight) way. I'm curious... 1. Did you direct-bry the coax? I've had people tell me to go ahead and bury it. They say that by the time the coax deteriorates I should have replaced it anyway. On the other hand, you can buy poly hose pretty cheap. That would keep the lines dry and protect them from an errant shovel or two. 2. How bad is it to run various lines together in a tube. Would I be better off to run them at least a few inches part to minimize inductive pickup? 3. Of course it would need to be separate but: Has anyone run ladderline underground? Theoretically it's possible but my intuition says "Don't do it!" 73, Mark W1EOF
Re: [AMRadio] antenna tuners
- Original Message - Subject: [AMRadio] antenna tuners > I don't believe in them. > > If you can't resonate your antenna, then what are you doing? There is an antenna that will require tuning components at the feedpoint even at perfect resonance: the folded unipole. This is a vertical antenna that is commonly used in AM broadcasting. It is physically shorter than a standard 1/4 wavelength series-fed vertical and consists of a grounded tower with a skirt of wires around it. The wires are held away from the tower members with insulating spacers that are about 1 meter long. A ring of wire connects the three skirt wires together and this is then connected to the tower as the "commoning" ring. The bottoms of the skirt wires are also joined by a ring of wire, but this is kept insulated from the tower and serves as the feedpoint. If the commoning ring is placed at the proper spot along the skirt, the resistance will be 50 ohms. But a tuning network (or at least a capacitor) will be needed at the feedpoint, as folded unipoles have a lot of inductive reactance. This is an efficient antenna that provides excellent bandwidth. Come to think of it, even a standard series-fed vertical will need some impedance matching, as a 1/4 wave vertical antenna working against a good ground system will have an impedance of 35 ohms. Modern rigs require a load of 50 j0 ohms. Electrically short antennas are less efficient than their full-sized counterparts. But city dwellers and others who, for various reasons, cannot put up a standard antenna, will get decent results with short antennas and "antenna tuners". Phil K2PG
RE: [AMRadio] antenna tuners
This is another tidbit to keep in mind for those that still may think that an antenna has to be resonant to give 1:1 swr. A dipole antenna rarely is 50 ohms at resonance. It is very dependent on height above ground as to what impedance it presents at the feed point. It can range anywhere from below 30 ohms to above 70 ohms. So if you cut your antenna so that you have 1:1 swr at the transmitter end of the coax, the antenna is probably not tuned to resonance! You have detuned the antenna to change its impedance that the coax sees. Only rarely does a resonant antenna turn out to be 50 ohms. 73 Gary K4FMX
Re: [AMRadio] antenna tuners
Could you please explain, using an MFJ antenna analyzer, what is the meter showing on the instrument? I would think that the total system, that is feedline and flat top or antenna if you prefer, is resonating at the point shown on the meter? Or am I wrong? In any case, I love that device for checking out the "resonant" point of the antenna system - note that I did not say just antenna. Thank you Dave, W3ST Publisher of the Collins Journal Secretary to the Collins Radio Association www.collinsra.com - the CRA Website Now with PayPal CRA Nets: 3805 Khz every Monday at 8 PM EST and 14255 every Saturday at 12 Noon EST - Original Message - From: "Gary Schafer" <[EMAIL PROTECTED]> To: "'Discussion of AM Radio'" Sent: Thursday, April 20, 2006 10:12 PM Subject: RE: [AMRadio] antenna tuners This is another tidbit to keep in mind for those that still may think that an antenna has to be resonant to give 1:1 swr. A dipole antenna rarely is 50 ohms at resonance. It is very dependent on height above ground as to what impedance it presents at the feed point. It can range anywhere from below 30 ohms to above 70 ohms. So if you cut your antenna so that you have 1:1 swr at the transmitter end of the coax, the antenna is probably not tuned to resonance! You have detuned the antenna to change its impedance that the coax sees. Only rarely does a resonant antenna turn out to be 50 ohms. 73 Gary K4FMX __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
RE: [AMRadio] antenna tuners
Hi Dave, What the MFJ will show you at the end of your feed line is the result of the feed line and antenna as you noted. The only way to know where the antenna itself is resonant is to measure it right at the antenna. Or you can measure it through a 1/2 wave length of feed line which will reflect what is at the antenna to the other end. However that is only good at one frequency, where the feed line is exactly 1/2 wave length. A coax length of anything other than a 1/2 wave length is going to transform the impedance seen at the antenna (if it is not 50 ohms) to something else at the other end of it. By having the meter in the shack showing a low swr or finding the frequency where the swr dips does not mean that is where the antenna is resonant. It only means that is the frequency where the impedance is transformed to best match the transmitter. It is not necessarily the resonant frequency of the antenna. If the antenna resistance at resonance is not 50 ohms, changing its length (or frequency) will introduce reactance which adds or subtracts from the resistance until it presents 50 ohms at a particular frequency. Note that it will present 50 ohms to the feed line but it will no longer be resonant. 73 Gary K4FMX > -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of david knepper > Sent: Friday, April 21, 2006 5:22 AM > To: [EMAIL PROTECTED]; Discussion of AM Radio > Subject: Re: [AMRadio] antenna tuners > > Could you please explain, using an MFJ antenna analyzer, what is the meter > showing on the instrument? > > I would think that the total system, that is feedline and flat top or > antenna if you prefer, is resonating at the point shown on the meter? Or > am > I wrong? In any case, I love that device for checking out the "resonant" > point of the antenna system - note that I did not say just antenna. > > > Thank you > > Dave, W3ST > Publisher of the Collins Journal > Secretary to the Collins Radio Association > www.collinsra.com - the CRA Website > Now with PayPal > CRA Nets: 3805 Khz every Monday at 8 PM EST > and 14255 every Saturday at 12 Noon EST > - Original Message - > From: "Gary Schafer" <[EMAIL PROTECTED]> > To: "'Discussion of AM Radio'" > Sent: Thursday, April 20, 2006 10:12 PM > Subject: RE: [AMRadio] antenna tuners > > > > This is another tidbit to keep in mind for those that still may think > that > > an antenna has to be resonant to give 1:1 swr. > > > > A dipole antenna rarely is 50 ohms at resonance. It is very dependent on > > height above ground as to what impedance it presents at the feed point. > It > > can range anywhere from below 30 ohms to above 70 ohms. > > > > So if you cut your antenna so that you have 1:1 swr at the transmitter > end > > of the coax, the antenna is probably not tuned to resonance! You have > > detuned the antenna to change its impedance that the coax sees. > > > > Only rarely does a resonant antenna turn out to be 50 ohms. > > > > 73 > > Gary K4FMX > > > > > > __ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
Re: [AMRadio] antenna tuners
Gary K4FMX said: By having the meter in the shack showing a low swr or finding the frequency where the swr dips does not mean that is where the antenna is resonant. It only means that is the frequency where the impedance is transformed to best match the transmitter. It is not necessarily the resonant frequency of the antenna. Would you agree that if the SWR was less than 1.5:1 at a given frequency that one could say that the "ANTENNA SYSTEM" was resonant at that frequency? Would you also agree that the antenna would take the same amount power, minus the feedline loss, as if the antenna were resonant? 73, Ken W2DTC
RE: [AMRadio] antenna tuners
> -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of kenw2dtc > Sent: Friday, April 21, 2006 11:31 AM > To: [EMAIL PROTECTED]; Discussion of AM Radio > Subject: Re: [AMRadio] antenna tuners > > Gary K4FMX said: > > > By having the meter in the shack showing a low swr or finding the > > frequency > > where the swr dips does not mean that is where the antenna is resonant. > It > > only means that is the frequency where the impedance is transformed to > > best > > match the transmitter. It is not necessarily the resonant frequency of > the > > antenna. > > Would you agree that if the SWR was less than 1.5:1 at a given frequency > that one could say that the "ANTENNA SYSTEM" was resonant at that > frequency? Would you also agree that the antenna would take the same > amount > power, minus the feedline loss, as if the antenna were resonant? > > 73, > Ken W2DTC You could say anything you want. You could employ an antenna tuner to an antenna and line that by themselves have 20:1 swr at 50 ohms and tune the tuner until there is 1:1 coming out of it. You could then say that your "antenna system" was resonant. If the plate tuning network on your transmitter would match that same antenna and feed line directly without the antenna tuner, you could again say that your "antenna system" was resonant. It all depends on how much you want to include as your "antenna system". As long as you don't confuse yourself as to what is really happening at the antenna itself. My original comments were addressing the question of whether or not the antenna itself needed to be resonant for maximum performance. Which it does not have to be. Antenna resonance has nothing to do with the "amount of power that an antenna will take". The amount of power it will take has only to do with the construction of the antenna itself. Will it arc somewhere or melt the wire down etc. The amount of power that the feed line will take (over a flat line)is largely determined by the swr on the line. How hot it will get from the added current as a result of the swr or if it will arc from the added voltage due to high swr. 73 Gary K4FMX
Re: [AMRadio] antenna tuners
I was beaten to the door on this. Actually there is a spot up about one third wavelength that is 100 ohms,for a perfectly resonate radiator. So it would be 2 to one and a dandy perfect resonate vertical with over a hundred radials is about 35 ohms so the magical 1 to 1 is nothing magical. I would beg everybody to read at least two chapters of Walt Maxwell's book " Reflections". The right SWR for the wrong reason, and the Wrong SWR for the right reason. The first I would call dummy load syndrome and the second as above. This stuff is not opinion or politics it is pure science and can be tested at YOUR house.. 73 Mike - Original Message - From: "Gary Schafer" <[EMAIL PROTECTED]> To: "'Discussion of AM Radio'" Sent: Thursday, April 20, 2006 10:12 PM Subject: RE: [AMRadio] antenna tuners > This is another tidbit to keep in mind for those that still may think that > an antenna has to be resonant to give 1:1 swr. > > A dipole antenna rarely is 50 ohms at resonance. It is very dependent on > height above ground as to what impedance it presents at the feed point. It > can range anywhere from below 30 ohms to above 70 ohms. > > So if you cut your antenna so that you have 1:1 swr at the transmitter end > of the coax, the antenna is probably not tuned to resonance! You have > detuned the antenna to change its impedance that the coax sees. > > Only rarely does a resonant antenna turn out to be 50 ohms. > > 73 > Gary K4FMX > >
RE: [AMRadio] antenna tuners
From: "Gary Schafer" <[EMAIL PROTECTED]> > Another factor causing loss with a high SWR is dielectric losses at the > recurring high rf voltage points along the line. At low impedances, it is > the resistive loss in the wire, and at high impedances, it is dielectric > losses that combine to cause signal loss. But SWR is much, much less > critical than most hams have been led to believe. It is my understanding that at HF only resistive loss comes into play. Dielectric loss isn't a problem until you get into vhf. I would say it depends on what kind of balanced line you use. If it is well insulated, real open wire line, with ceramic or low-loss plastic spreaders, there is probably negligible dielectric loss at hf or even lower vhf. But if it is solid dielectric feedline, or even that pseudo-open wire line stuff that is basically heavy duty TV lead-in with square holes punched in the dielectric, I suspect there would be dielectric losses even at hf, and that they would increase with substantial SWR. The same goes for solid dielectric or foam type coax. However, for moderate SWR's, the loss is much less serious than most hams have been led to believe. Don k4kyv ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
Re: [AMRadio] antenna tuners
> I don't believe in them. > > If you can't resonate your antenna, then what are you doing? I prefer to use just one dipole, centre-fed with open wire line, and use multiband tuners to operate that same antenna on several bands. That way it is uniformly efficient all the way across each band, and I don't have the clutter of multiple dipoles strung all around each other, or the compromise of an "all-band" antenna such as a trap dipole. With a proper tuner, the antenna, feedline and ATU all make up a resonant system. Resonance can be changed by changing the length of the antenna, the length of the feedline, or the adjustment of the tuner, but it's the whole system that is placed in resonance, not just the antenna wire itself, as in the case of a simple coax-fed dipole. Don k4kyv ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
Re: [AMRadio] antenna tuners
Don your comments remind me of the time I visited the QTH of Bob, W5PYT. El Paso Natural Gas had abandoned the microwave system leaving a 200 ft. tower that supported the dishes vacant. Bob talked them into letting him use it for antennas and support. He had so many antennas strung up on it that a bird couldn't fly within 1000 ft. of it unless they were sliced like a loaf of bread. I can imagine Bob pruning each antenna following installation of something new to achieve maximum radiation. He always had a good signal though. Boy what a mess it was. 73 Jim W5JO I prefer to use just one dipole, centre-fed with open wire line, and use multiband tuners to operate that same antenna on several bands. That way it is uniformly efficient all the way across each band, and I don't have the clutter of multiple dipoles strung all around each other, or the compromise of an "all-band" antenna such as a trap dipole. Don k4kyv
RE: [AMRadio] antenna tuners
> -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Donald Chester > Sent: Friday, April 21, 2006 7:56 PM > To: amradio@mailman.qth.net > Subject: Re: [AMRadio] antenna tuners > > > > > I don't believe in them. > > > > > > If you can't resonate your antenna, then what are you doing? > > > I prefer to use just one dipole, centre-fed with open wire line, and use > multiband tuners to operate that same antenna on several bands. That way > it > is uniformly efficient all the way across each band, and I don't have the > clutter of multiple dipoles strung all around each other, or the > compromise > of an "all-band" antenna such as a trap dipole. > > With a proper tuner, the antenna, feedline and ATU all make up a resonant > system. Resonance can be changed by changing the length of the antenna, > the > length of the feedline, or the adjustment of the tuner, but it's the whole > system that is placed in resonance, not just the antenna wire itself, as > in > the case of a simple coax-fed dipole. > > Don k4kyv Hi Don, Let's say you changed the output impedance of your transmitter from 50 ohms to say 200 ohms. (changing nothing on the tuner) Would the "antenna system" (antenna, feed line and tuner) still be "resonant" as you had them tuned when you had the transmitter set for 50 ohms output? If you now retune the antenna tuner to accommodate the 200 ohm output of the transmitter, will the "antenna system" again be resonant? :>) :>) 73 Gary K4FMX
RE: [AMRadio] antenna tuners
> -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Donald Chester > Sent: Friday, April 21, 2006 7:15 PM > To: amradio@mailman.qth.net > Subject: RE: [AMRadio] antenna tuners > > >From: "Gary Schafer" <[EMAIL PROTECTED]> > > > > Another factor causing loss with a high SWR is dielectric losses at > the > > > recurring high rf voltage points along the line. At low impedances, > it > >is > > > the resistive loss in the wire, and at high impedances, it is > dielectric > > > losses that combine to cause signal loss. But SWR is much, much less > > > critical than most hams have been led to believe. > > > >It is my understanding that at HF only resistive loss comes into play. > >Dielectric loss isn't a problem until you get into vhf. > > I would say it depends on what kind of balanced line you use. If it is > well > insulated, real open wire line, with ceramic or low-loss plastic > spreaders, > there is probably negligible dielectric loss at hf or even lower vhf. But > if it is solid dielectric feedline, or even that pseudo-open wire line > stuff > that is basically heavy duty TV lead-in with square holes punched in the > dielectric, I suspect there would be dielectric losses even at hf, and > that > they would increase with substantial SWR. > > The same goes for solid dielectric or foam type coax. > > However, for moderate SWR's, the loss is much less serious than most hams > have been led to believe. > > Don k4kyv Actually the dielectric losses don't have much effect until high vhf and into UHF. Changing the dielectric material in coax from a solid to air dielectric where there is very little dielectric material, makes no significant difference in loss at HF. But the reason the loss goes down with air dielectric is because the center conductor is made larger and has less resistance loss. The center conductor has to be made larger to maintain the same impedance line. I think I read somewhere that the open wire line with the holes punched in the dielectric was no better as far as loss goes than if the holes were not there. But punching the holes allows for a little higher impedance line by lowering the capacitance so that lowers the loss. But the presence of less dielectric material itself had no effect on loss. Real open wire line will usually have less loss than the TV style line with the solid or punched dielectric between the wires because real open wire line will have a higher impedance than the other stuff. Usually the TV style line even if advertised as 600 ohm line is lower impedance. The punched hole stuff I think is advertised as 450 ohm line but turns out to be lower than that. 73 Gary K4FMX
RE: [AMRadio] antenna tuners
From: "Gary Schafer" <[EMAIL PROTECTED]> Let's say you changed the output impedance of your transmitter from 50 ohms to say 200 ohms. (changing nothing on the tuner) Would the "antenna system" (antenna, feed line and tuner) still be "resonant" as you had them tuned when you had the transmitter set for 50 ohms output? The antenna system might still be in resonance, depending on what the reflected power on the open wire line "sees" when reflected back to the transmitter output. The transmitter puts a load, with a specific impedance, on the transmit end of the feedline just as the antenna puts a load on the antenna end. It's possible that the impedance that the transmitter presents to the feedline could have a combination of reactance and resistance that would alter the resonant frequency of the system. Another possibility is that it would stay in resonance, with no reactive component, but due to the load mismatch, there would be a reduction in coupling so that the transmitter would not load up to full power. A comparable example would be, if the above system used a balanced tuner with swinging link: You could tune the tuner to resonance, and then vary the link to achieve just the right amount of coupling to load the final to the desired load. Moving the link in or out would vary the load on the final, and thus final amp plate courrent, but if everything is tuned up to cancel out the reactance, after you vary the coupling with the link, you would re-check the dip at the final amplifier, and it would still be dipped at resonance, ever though the final might be loaded more lightly or heavily. I can do the same thing with my link coupled tranmitters. Adjust the tuner to resonance, which usually gives maximum coupling to the final. Dip the final. Now re-tune the antenna tuner. Adjusting the antenna tunerl should give a peak plate current, while adjusting the final amp plate tank cap gives a dip to the plate current. If everything is tuned to resonance, tune the ant tuner to peak plate current. Now re-check dip. It should still be dipped to resonance. Now adjust the link coupling. The plate current will increase or decrease, depending on whether the link is moved in or out of the coil. But once the coupling is changed, the PA plate current should still be very close to the minimum point (dip). If it is not at resonance, changing the loading with the link will require retuning the PA plate tank cap to resonance to maintain the PA plate current dip. If that is the case, no problem. Re-dipping the final brings the system back into resonance. With my link coupled transmitters, I usually have to touch up the dip after I change coupling with the link. The point is, adjusting any one or combination of the following: the PA tank settings, the antenna tuner settings, the antenna turner coupling coil (if link coupling is used), the length of the open wire feeder, the length of the antenna, will affect the resonant frequency and thus the reactance vs resistance of the network that couples the amplifying device at the final amplifier to the aether. Don k4kyv ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
RE: [AMRadio] antenna tuners
> > The point is, adjusting any one or combination of the following: the PA > tank > settings, the antenna tuner settings, the antenna turner coupling coil (if > link coupling is used), the length of the open wire feeder, the length of > the antenna, will affect the resonant frequency and thus the reactance vs > resistance of the network that couples the amplifying device at the final > amplifier to the aether. > > Don k4kyv > The question was meant to invoke some thought about what parts of the system come into play when we say things are "resonant". As we see from Don's explanation we can go right down to the final tank circuit when talking about making the antenna system resonant. The following will be true when the tuner is adjusted to provide a non reactive 50 ohm output to the transmitter: Assuming a 50 ohm link, if the link in the final is resonant (reactance is zero) then once the plate is dipped, moving the link to change coupling should not change plate resonance. If the link is not resonant then it will affect the plate circuit resonance when its coupling is changed. If the antenna tuner does not match the link on the transmitter the link will have a reactive component that will effect transmitter plate tuning. Now the transmitter plate tuning will be part of the whole "antenna system resonance". This is why I don't like to refer to the "antenna system" being resonant. Too many things can be involved and we loose sight of what we really mean. The same is true if you feed a coax fed dipole directly from the pi network output of your transmitter. Or use a tuner that is not tuned for a flat match to the transmitter. The plate and load tuning becomes part of the "antenna system tuning" if you are to use that terminology. If we think of feed lines as transformers (whether they are open wire or coax) and antenna tuners as variable transformers it makes things easier to see. When using an antenna tuner and we tune the reactance out of the circuit so we only see a resistive component we can say it is resonant. But what is really resonant? The antenna is not, the feed line is not, the tuner is not. The only thing resonance means in this case is that the capacitive and inductive reactances at the tuner are equal. It confuses many people. 73 Gary K4FMX
RE: [AMRadio] antenna tuners...
My heathkit antenna tuner has worn out I think, I built it 20 years ago or more, and I think its shot. All the silver plating has worn off the roller bar, which sometimes results in an open which blows the diodes out in the swr bridge. I took it apart and cleaned things up, but I think its time for a new tuner. I would also like to be able to bypass the tuner without moving coax, so the rigs with built in tuners can do their automatic thing. For unbalanced antenna's, what is available that can handle say 3000 watts pep? Some headroom is a good thing, no? I know better then to buy anything MFJ... Anything out there that holds up to AM? Brett N2DTS __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
Re: [AMRadio] antenna tuners...
Take a look at Palstar. http://www.palstar.com Then take a look at your bank account. :-) Best Regards, Stevan A. White, W5SAW SW Commercial Electronics 928 South Crockett Street Amarillo, Texas 79102 Phone 806-681-7228 [EMAIL PROTECTED] "You can tell more about a person by what he says about others than you can by what others say about him." -- Leo Aikman, Writer and Newspaper Editor Brett gazdzinski wrote: My heathkit antenna tuner has worn out I think, I built it 20 years ago or more, and I think its shot. All the silver plating has worn off the roller bar, which sometimes results in an open which blows the diodes out in the swr bridge. I took it apart and cleaned things up, but I think its time for a new tuner. I would also like to be able to bypass the tuner without moving coax, so the rigs with built in tuners can do their automatic thing. For unbalanced antenna's, what is available that can handle say 3000 watts pep? Some headroom is a good thing, no? I know better then to buy anything MFJ... Anything out there that holds up to AM? Brett N2DTS __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body. __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
RE: [AMRadio] antenna tuners...
Yes, well... At those prices, I suppose one could build a nice tuner from parts. $1195.00 plus shipping for the 3500, I think the most expensive part would be a big edge wound roller inductor. I wonder if a tapped coil (copper tubing) would be good enough, I have seen some units that have a band switch for the inductor. I think you would have less problems with a big copper coil and a massive switch, and my heathkit tuner seems to want the same roller inductor setting (roughly) no matter what antenna, 121 on 80, 68 on 40 and it does not seem to change much from that. Or maybe I should just get a Johnson KW matchbox You can do balanced or unbalanced with them, right? Brett N2DTS > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Stevan A. White > Sent: Wednesday, April 11, 2007 3:10 PM > To: Discussion of AM Radio in the Amateur Service > Subject: Re: [AMRadio] antenna tuners... > > Take a look at Palstar. http://www.palstar.com Then take a look at > your bank account. :-) > > Best Regards, > Stevan A. White, W5SAW > SW Commercial Electronics > 928 South Crockett Street > Amarillo, Texas 79102 > Phone 806-681-7228 > [EMAIL PROTECTED] > > "You can tell more about a person by what he says about > others than you > can by what others say about him." -- Leo Aikman, Writer and > Newspaper > Editor > > > > Brett gazdzinski wrote: > > My heathkit antenna tuner has worn out I think, > > I built it 20 years ago or more, and I think its shot. > > > > All the silver plating has worn off the roller bar, which > > sometimes results in an open which blows > > the diodes out in the swr bridge. > > > > I took it apart and cleaned things up, but I think > > its time for a new tuner. > > I would also like to be able to bypass the tuner without > > moving coax, so the rigs with built in tuners can > > do their automatic thing. > > > > > > For unbalanced antenna's, what is available that can handle say > > 3000 watts pep? > > > > Some headroom is a good thing, no? > > > > I know better then to buy anything MFJ... > > > > Anything out there that holds up to AM? > > > > Brett > > N2DTS > > > > > > __ > > AMRadio mailing list > > List Rules (must read!): http://w5ami.net/amradiofaq.html > > List Home: http://mailman.qth.net/mailman/listinfo/amradio > > Partner Website: http://www.amfone.net > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > To unsubscribe, send an email to > [EMAIL PROTECTED] with > > the word unsubscribe in the message body. > > > > > __ > AMRadio mailing list > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Partner Website: http://www.amfone.net > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > To unsubscribe, send an email to [EMAIL PROTECTED] with > the word unsubscribe in the message body. > __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
Re: [AMRadio] antenna tuners...
Nye Viking MBV-A comes to mind as a good, sturdy tuner that will handle a good deal of power without complaint. I've had such good luck with my HB link-coupled tuner that I have not used my MBV-A for a couple of years, but for coax feed I certainly would use it. I've seen these tuners for sale several times recently for a good deal less money than some other tuners go for. 73, Barrie, W7ALW __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
Re: [AMRadio] antenna tuners...
Brett... How about an EF Johnson Matchbox? Not a bad tuner at all. Functional and versatile. Vitually plug-n-play. Better still, find a c.1950's Handbook or W6SAI's book(s) and design one. Troll ebay using the "ham radio" search and "parts" as your subject. A good RF switch wil handle the bypass requirement. Choose a "T" or "Pi" design that fits ur needs and cobble it together. I'd predict you'll have a great tuner. I happen to be watching a local ham buddie putting one together that will easily handle 5kw. Vacuum variable caps and a nice variable inductor. He plans on tuning from 2-30mc with it with no more than 1kw. Plenty of headroom. 73 de W4MIL Chuck -Original Message- From: [EMAIL PROTECTED] To: amradio@mailman.qth.net Sent: Wed, 11 Apr 2007 2:42 PM Subject: RE: [AMRadio] antenna tuners... My heathkit antenna tuner has worn out I think, I built it 20 years ago or more, and I think its shot. All the silver plating has worn off the roller bar, which sometimes results in an open which blows the diodes out in the swr bridge. I took it apart and cleaned things up, but I think its time for a new tuner. I would also like to be able to bypass the tuner without moving coax, so the rigs with built in tuners can do their automatic thing. For unbalanced antenna's, what is available that can handle say 3000 watts pep? Some headroom is a good thing, no? I know better then to buy anything MFJ... Anything out there that holds up to AM? Brett N2DTS __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body. AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com. __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
Re: [AMRadio] antenna tuners...
The W1IA homebrew tuner would hold up to 3 kW. Joe W4AAB - Original Message - From: "Brett gazdzinski" <[EMAIL PROTECTED]> To: "'Discussion of AM Radio in the Amateur Service'" Sent: Wednesday, April 11, 2007 1:42 PM Subject: RE: [AMRadio] antenna tuners... > My heathkit antenna tuner has worn out I think, > I built it 20 years ago or more, and I think its shot. > > All the silver plating has worn off the roller bar, which > sometimes results in an open which blows > the diodes out in the swr bridge. > > I took it apart and cleaned things up, but I think > its time for a new tuner. > I would also like to be able to bypass the tuner without > moving coax, so the rigs with built in tuners can > do their automatic thing. > > > For unbalanced antenna's, what is available that can handle say > 3000 watts pep? > > Some headroom is a good thing, no? > > I know better then to buy anything MFJ... > > Anything out there that holds up to AM? > > Brett > N2DTS > > > __ > AMRadio mailing list > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Partner Website: http://www.amfone.net > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > To unsubscribe, send an email to [EMAIL PROTECTED] with > the word unsubscribe in the message body. > __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
RE: [AMRadio] antenna tuners...
I need one that has a switch for the band, changing coil taps, and the caps for tuning. I have not looked at designs yet, except that the heathkit is a T config, roller inductor goes to ground. I have been jumping around a lot between 40 and 80 meters, AM and CW segments of both bands, which requires me to tune the G5RV antenna up, and the heathkit is worn out. It works ok on low power, but on higher power its got issues. It seems to me like a switch would be a lot easier and longer lasting than spinning a roller inductor endlessly. If I make a tuner, I can make the coil large and out of copper tubing for low loss, figuring out the taps for each band might be hard though. Guess I should look on ebay for a big switch tuner, I saw a Millen large one, but did not bid on it. I did not know Millen made a tuner... Brett N2DTS > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Barrie Smith > Sent: Wednesday, April 11, 2007 4:10 PM > To: Discussion of AM Radio in the Amateur Service; [EMAIL PROTECTED] > Subject: Re: [AMRadio] antenna tuners... > > Nye Viking MBV-A comes to mind as a good, sturdy tuner that > will handle a > good deal of power without complaint. > > I've had such good luck with my HB link-coupled tuner that I > have not used > my MBV-A for a couple of years, but for coax feed I certainly > would use it. > > I've seen these tuners for sale several times recently for a > good deal less > money than some other tuners go for. > > 73, Barrie, W7ALW > > > __ > AMRadio mailing list > List Rules (must read!): http://w5ami.net/amradiofaq.html > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Partner Website: http://www.amfone.net > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > To unsubscribe, send an email to [EMAIL PROTECTED] with > the word unsubscribe in the message body. > __ AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
RE: [AMRadio] antenna tuners transmision lines and more
or vacuum type with good aluminum plates) have little or no measurable loss. They give almost 100% of the energy they absorb back to the load or source. They are adjusted with the inductors so as to send the energy to the load and not the source. 2. Air inductors are also almost lossless except for a small amount due to the resistance of the material. The energy they absorb is stored magnetically and almost all given back to the load or source. They also are adjusted with the capacitors so as to send the energy to the load and not the source. 3. Antenna systems (including tuners) are made of material that is very low in resistance to electron flow (or they should be). With the above facts in mind, consider the following scenario. 1. A transmitter is connected to an antenna system made with quality components 2. The finals are not dissipating any more heat than they would if connected to a perfect dummy load. 3. There is no measurable heat dissipated in any of the components of the antenna system. Then the energy that is produced from the finals must be being used by something irregardless of resonance. The energy must be going to out into space because nothing is dissipating any heat that we can measure and it makes no difference what length the antenna is because th tuner is compensating for the reactance and transforming the current to voltage ratios as needed to get the energy out. It is being radiated, hence the term "radiation resistance". Most folks mistakenly think of the term radiation resistance as a fixed value of 73 Ohms. BUT THIS IS NOT TRUE. 73 Ohms is the radiation resistance of a center fed 1/2 wave dipole in free space and by the way increasing the size of the wire has very little effect on it. A center fed full wave dipole will radiate the same amount of energy but has a much higher radiation resistance. It has no greater or less radiation efficiency than does the 1/2 wave dipole (negligible copper resistance loss). It just radiates in a slightly different pattern. Theoretical, (neglecting copper losses) if all of the energy of the radiated signal could be recaptured and measured from each of the two antennas the measured amounts would be equal. Here is some question that I have never learned the answer to. I have never seen a value of radiation resistance assigned to a center fed full wave dipole. Perhaps it is too difficult to measure? As Don,K4KYV pointed out, "There has to be some current flow there, else there would be no power transferred" I would also like to know the theoretical feed point resistance of a theoretically infinite length dipole and why a rhombic is terminated with a 600 ohm resistor instead of, for the sake of argument, say a 100 Ohm resistor or some other value. I understand that Rhombic and long wires (10 wave lengths or more) radiate 90% of there energy before the signal reaches the end of the wires. And that the terminating resistor is there to lower reflections that might make the antennas bi-directional. So could that mean that 600 ohms is about the Radiation resistance of a infinite length of wire? Here is a little tidbit that may not be well known. Don, K4KYV, once explained to me, the reason for the 300 ohm feed point of the folded dipole. It went like this. There or two wires which must divide there current evenly. Consider a 100 watt carrier gong into a 1/2 wave dipole. With the 73 ohm radiation resistance the current at the feed point would be about 1.17 Amps and the voltage would be 85.4 Volts If another wire is added to make the antenna into a folded dipole then each wire would have a current at the center of (1.17 / 2) or .585 Amps. But since only one wire is fed then in order to get the 100 watt value the voltage must be double to 170.8 volts. R = E/I so 170.8 volts divided by .585 Amps equals about 292 Ohms. Hence the value rounded to 300 Ohms. It is some what like an impedance ratio of 1:4 for a 2 wire folded dipole. In a 3 wire folded dipole the currents will be divided by thirds per wire. This will work out to near 600 Ohms for a 3 wire folded dipole. ** -Original Message--Edited for space--- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gary Schafer Sent: Sunday, April 23, 2006 11:49 AM To: 'Discussion of AM Radio' Subject: RE: [AMRadio] antenna tuners When using an antenna tuner and we tune the reactance out of the circuit so we only see a resistive component we can say it is resonant. But what is really resonant? The antenna is not, the feed line is not, the tuner is not. The only thing resonance means in this case is that the capacitive and inductive reactances at the tuner are equal. It confuses many people. 73 Gary K4FMX
RE: [AMRadio] antenna tuners transmision lines and more
Very nice work, thanks for taking the time to write this Brad KB7FQR -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Coleman ARS WA5BXO Sent: Sunday, April 23, 2006 4:59 PM To: 'Discussion of AM Radio' Subject: RE: [AMRadio] antenna tuners transmision lines and more You are correct Gary, it is very confusing to many and I was one confused guy for many years. It's not easy to get a grip on things of this nature. Invisible radiation and weird parts that have no movement, makes it all seem like wizardry and magic. Of course this is what makes it fascinating. I'll just add some more to the confusion. I am by no way a XPERT on this stuff but I have been told that I have a way with words as long as I can get a spell checker working. I have been asked to do some of this writing. I feel that I should share this with others and I have chosen this place to do it. I don't have a lot of opportunity to go get on the air much any more. I get stuck here at home watching kids once in a while and so this is when I type up these long stories. So please excuse the long winded transmission here. I hope some one gets something from it. Old Wives Tales (Misleading statements) FALSE STEAMENT #1 -- A high SWR reading is an indication that a lot of power is wasted and not being radiated. - TRUE STATEMENT --- SWR is the ratio of currents measured at physical points on a transition line. It is the ratio of the maximum current on the line verses the minimum current on the line. These two physical points will be 1/4 electrical wavelength apart. They do not necessarily have to be at the load end or the source end. IF the load end is representative of a pure resistive load then the SWR will be the ratio of the load resistance to the line characteristic impedance. If the load resistance is non reactive and equal to the line characteristic impendence then the SWR is 1:1 and current will be the same at any point on the transmission line that you care to measure it except for the normal loss due to line characteristics. Even a perfectly matched load:line such will have slightly less current and voltage at the load end than at the source end although as some one earlier pointed out, "It is generally a negligible difference". It would need to be a very long line to be significant on 80 or 40 meters. FALSE STATEMENT #2 --- There is no need for a tuner if the antenna is resonate and the line is matched. TRUE STATEMENT -- If the antenna feed point is equal to the line Z and the transmitter is made to work into this load then there may be no need for a tuner. This is an almost impossible task as some one pointed out earlier, and even if it were to be done it would only be true for a very small range of frequencies. QSY would be a compromise. FALSE STATEMENT #3 --- Tuners waste a lot of power and just make the transmitter think the antenna is right. TRUE STATEMENT --- A tuner consists of coils and capacitors neither of which by mathematical definition consumes energy. The adjustments of the coils and capacitors change the phase as well as the voltage to current ratios of input and output. The slight amount of energy that may be consumed by tuners is generally so negligible that it is very difficult to measure. In some cases a tuners components maybe made of poor quality material and too small for the job. These types of components will get hot. Heat is an obvious point of loss. I had a small MFJ tuner that was manufactured some years ago. It was just a small external Pi-Net device and I found it to have a measurable insertion loss. It turned out to be the rivets that held the connectors on the little chassis. I soldered braid across the connectors to the chassis and then the loss was then immeasurable. Modern solid state equipment is designed to work into a 50 ohm non reactive load. Connecting a dummy load of 60 ohms instead of 50 ohms will cause the rig to put out less RF current and make the automatic drive level circuitry start pulling back on drive prematurely. If the load becomes slightly reactive as well then the RF production will decrease rapidly. A tuner is nearly a must for these rigs. In tube type XMTRs the use of toroidal transformers for the output is impossible because of the high output Z of tubes. These rigs used instead a Pi-NET or link coupled tuned circuitry to do the job of matching the tube to the low impedance output. This type of circuitry could match a relatively wide range of impedances from 25 ohms to several hundred ohms as well as compensate for some reactance. Because of this an external tuner may not have been necessary especially if confined to one band on one antenna. A lot of folks put up multiple antennas one for each band or used a multiband trapped dipole or some other multiband radiator with a single coaxial down line. The Pi-Net in the rig did all the com
RE: [AMRadio] antenna tuners transmision lines and more
t divide there current evenly. > > Consider a 100 watt carrier gong into a 1/2 wave dipole. > > With the 73 ohm radiation resistance the current at the feed point would > be about 1.17 Amps and the voltage would be 85.4 Volts > > If another wire is added to make the antenna into a folded dipole then > each wire would have a current at the center of (1.17 / 2) or .585 Amps. > > But since only one wire is fed then in order to get the 100 watt value > the voltage must be double to 170.8 volts. > > R = E/I so 170.8 volts divided by .585 Amps equals about 292 Ohms. > Hence the value rounded to 300 Ohms. > > It is some what like an impedance ratio of 1:4 for a 2 wire folded > dipole. > > In a 3 wire folded dipole the currents will be divided by thirds per > wire. This will work out to near 600 Ohms for a 3 wire folded dipole. > > > > > > > ** > > > -Original Message--Edited for space--- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Gary Schafer > Sent: Sunday, April 23, 2006 11:49 AM > To: 'Discussion of AM Radio' > Subject: RE: [AMRadio] antenna tuners > > > When using an antenna tuner and we tune the reactance out of the circuit > so > we only see a resistive component we can say it is resonant. But what is > really resonant? The antenna is not, the feed line is not, the tuner is > not. > > > The only thing resonance means in this case is that the capacitive and > inductive reactances at the tuner are equal. It confuses many people. > > 73 > Gary K4FMX > > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb >
RE: [AMRadio] antenna tuners transmission lines and more
Hi John, Boy you can tell you are an AM'r with the long post! :>) In some of the following I am saying the same thing as John with a little different explanation. Some is a bit of a correction. Lots of good stuff from John! I don't consider myself an expert either. This was going to be rather short but... SWR: The swr on a line can be found by measuring voltage peaks or current peaks on the line as you described. To truly measure swr the line must be at least a quarter wavelength long. What we normally measure with our swr meters or watt meters is an impedance ratio, which can be done on any length of line. The impedance ratios are representative of the standing wave ratios but we are not directly measuring standing waves. The impedances are compared to a resistor in the Swr Bridge. LINE LOSS: High swr "can" be an indication of wasted power but in the form of feed line loss if the feed line is a low impedance line such as coax. High swr can produce very currents on the line which result in I squared R loss. High swr on a higher impedance line is not usually much of a problem because the I squared R loss is much lower due to the current being less just because the line is higher impedance. TUNERS WASTING POWER: A tuner can dissipate substantial amounts of power depending on the load it is trying to match and if it is not adjusted properly. Even one with high quality components. For example the most common T type tuner can be misadjusted with the improper L /C ratios causing very circulating tank currents which heat the coil substantially. But if adjusted properly this is not usually a problem. REFLECTED POWER TO THE FINALS: As you noted high swr is an indication of reflected power on the feed line but that reflected power does not make it back to the finals in the transmitter. The reason it does not is because any reflected power that comes back down the line is re-reflected back to the antenna and eventually gets radiated. It gets re-reflected by what is called a conjugate match at the antenna tuner or the final tuning. A conjugate match presents an equal and opposite match to the line at the antenna tuner end of the line as what the mismatch to the line is at the antenna. If the line presents an inductive reactance at the tuner then the tuner must present an equal amount of capacitive reactance to the line. That is what some people call "resonance". That gives a flat, no swr, between the radio and the tuner. All the reflected power that came back to the tuner will be reflected back to the antenna at that point. RADIATION RESISTANCE: The definition of radiation resistance is, The total EM power radiated in all directions divided by the square of net current causing the radiation. In other words radiation resistance is equal to, a resistor if substituted for the antenna, that would absorb the same amount of power that the antenna radiates. Radiation resistance is not the feed point resistance of an antenna. The feed point resistance of an antenna also includes resistive losses in the wire. Power dissipated in that resistance is wasted in heat. FOLDED DIPOLE: The radiation resistance of a folded dipole is the same as that of a regular dipole. Even though the "feed point resistance" is 4 times as high for a folded dipole its radiation resistance is the same as a regular dipole. The folded element in the folded dipole only acts as an impedance transformer just like a 4:1 balun would do. The same holds true for a vertical monopole with a folded element to raise the feed point resistance. The radiation resistance is still the same as if the monopole were fed in the normal manor at the bottom against ground. SHORT ANTENNAS: A short antenna will radiate just as well as a full length antenna. As a matter of fact an infinitely small antenna will radiate just as well as a 1/4 wave or 1/2 wave length antenna. The problem is getting the power into the short antenna. A loaded mobile antennas radiation resistance is usually very low, in the order of a few ohms. Adding a loading coil to raise the feed point resistance to 50 ohms still leaves the radiation resistance of the antenna itself at those low few ohms to work against ground in getting power into the antenna for it to radiate. The coil dissipates most of the power applied in heat. If only 1 watt actually is radiated by a short mobile antenna it will produce the same signal strength as a full quarter wave length antenna with the same amount of power radiated. RADIATION RESISTANCE OF A FULL WAVE DIPOLE: I believe the radiation resistance of a 1/2 wave dipole is in the neighborhood of 2000 to 4000 ohms. I think it is the same as what the impedance at the end of a 1/2 wave antenna would be. I saw once how to calculate it. I will have to dig around again. Again I believe that an infinitely long dipole will have a similar radiation resistance to the full wave dipole. RHOMBIC ANTENNA: A rhombic is a different antenna than just a long dipole.
RE: [AMRadio] antenna tuners transmission lines and more
> -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Brian Carling > > The power may not be wasted very much in the tuner, BUT > REFLECTED power goes back into the RF final and is disippated > in the famil amplifier device(s) - at least many people have > written articles for decades describing that marticular "myth" > or so-called "FALSE STATEMENT." I am not so sure it is false > though! Look at your bird wattmeter, or any other directional wattmeter, in a line that shows reflected power. Note that the forward power reading will be higher than the actual power delivered by the transmitter. Example: If your transmitter puts out 100 watts and it feeds a load that presents 20 watts reflected, your wattmeter will read 120 watts forward and 20 watts reflected. If you look in the bird manual it will tell you to find the amount of power delivered to the load you subtract the reverse power reading from the forward reading. In this case you would subtract the 20 watts reflected from the 120 watt forward reading. That gives you 100 watts delivered to the load. The same amount of power that the transmitter is putting out. There is no reflected power left to get back to the finals! Prove it to yourself: Put a wattmeter at your transmitter. Run some coax to an antenna tuner, then another wattmeter, then a 50 ohm dummy load. Adjust the tuner so the first wattmeter shows 20 watts reflected and 120 watts forward. The wattmeter at the load will read 100 watts. The tuner is simulating a mismatched load while you are able to measure actual power into the load. Or you can use a non 50 ohm load and measure the voltage across that load to find actual power into the load. See my explanation in my other post about reflected power as to how it happens. 73 Gary K4FMX
RE: [AMRadio] antenna tuners transmision lines and more
From: "Brian Carling" <[EMAIL PROTECTED]> The power may not be wasted very much in the tuner, BUT REFLECTED power goes back into the RF final and is disippated in the famil amplifier device(s) - at least many people have written articles for decades describing that marticular "myth" or so-called "FALSE STATEMENT." I am not so sure it is false though! That is a myth. The power that is not radiated by the antenna or burnt up as resistive loss in the wire, goes back to tank circuit of the transmitter, contributes to the circulating rf current in the tank circuit, and is re-reflected back to the antenna. It may take several oscillations back and forth before all the energy is dissipated, but it is eventually dissipated in the antenna as radiated power and in the wire as resistive loss, not in the final amplifier tubes. The standing waves can be thought of as circulating current on the feedline. If the open wire line is left open with nothing connected, or if it is shorted, no rf escapes the feedline to excite an antenna. It is nearly all reflected back to the transmitter, and then back to the opposite end, until it is all dissipated as heat due to resistive losses. The current on the feeders, as measured with an rf ammeter, might be very high, but there is no radiation resistance or radiation. The rf ammeter may read seveal amperes while the final amp is dipped at resonance to near zero place current. There is very high circulating current in the tank circuit and the feeder, and at some points the voltage is very high - basically a Tesla coil, but negligible radiation. The myth I have often heard is that the rf is delivered back to the final and is dissipated in the plates of the output tubes. That is not true. If the plates of the tubes glow, it is due to plate dissipation (DC input to the final minus the power delivered to the tank circuit). This dissipation is due to operating conditions of the tube, not rf power being reflected back into the tube. Don k4kyv ___ This message was typed using the DVORAK keyboard layout. Try it - you'll like it. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/
RE: [AMRadio] antenna tuners transmision lines and more
rgy but > has a much higher radiation resistance. It has no greater or less > radiation efficiency than does the 1/2 wave dipole (negligible copper > resistance loss). It just radiates in a slightly different pattern. > > Theoretical, (neglecting copper losses) if all of the energy of > the radiated signal could be recaptured and measured from each of the > two antennas the measured amounts would be equal. > > > > Here is some question that I have never learned the answer to. > > I have never seen a value of radiation resistance assigned to a > center fed full wave dipole. Perhaps it is too difficult to measure? > As Don,K4KYV pointed out, "There has to be some current flow there, else > there would be no power transferred" > > I would also like to know the theoretical feed point resistance > of a theoretically infinite length dipole and why a rhombic is > terminated with a 600 ohm resistor instead of, for the sake of argument, > say a 100 Ohm resistor or some other value. > > I understand that Rhombic and long wires (10 wave lengths or > more) radiate 90% of there energy before the signal reaches the end of > the wires. And that the terminating resistor is there to lower > reflections that might make the antennas bi-directional. So could that > mean that 600 ohms is about the Radiation resistance of a infinite > length of wire? > > > Here is a little tidbit that may not be well known. > > Don, K4KYV, once explained to me, the reason for the 300 ohm > feed point of the folded dipole. It went like this. > > There or two wires which must divide there current evenly. > > Consider a 100 watt carrier gong into a 1/2 wave dipole. > > With the 73 ohm radiation resistance the current at the feed point would > be about 1.17 Amps and the voltage would be 85.4 Volts > > If another wire is added to make the antenna into a folded dipole then > each wire would have a current at the center of (1.17 / 2) or .585 Amps. > > But since only one wire is fed then in order to get the 100 watt value > the voltage must be double to 170.8 volts. > > R = E/I so 170.8 volts divided by .585 Amps equals about 292 Ohms. > Hence the value rounded to 300 Ohms. > > It is some what like an impedance ratio of 1:4 for a 2 wire folded > dipole. > > In a 3 wire folded dipole the currents will be divided by thirds per > wire. This will work out to near 600 Ohms for a 3 wire folded dipole. > > > > > > > ** > > > -Original Message--Edited for space--- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Gary Schafer > Sent: Sunday, April 23, 2006 11:49 AM > To: 'Discussion of AM Radio' > Subject: RE: [AMRadio] antenna tuners > > > When using an antenna tuner and we tune the reactance out of the circuit > so > we only see a resistive component we can say it is resonant. But what is > really resonant? The antenna is not, the feed line is not, the tuner is > not. > > > The only thing resonance means in this case is that the capacitive and > inductive reactances at the tuner are equal. It confuses many people. > > 73 > Gary K4FMX > > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
RE: [AMRadio] antenna tuners transmision lines and more
Thanks Don and Gary for a better description. Gary I really liked the descriptions and explanations of radiation resistance especially the one of the mobile antenna. That's the one thing that a lot of folks don't quite understand. It's what I call antenna efficiency. I've been told that the radiation resistance of an 80 meter base loaded mobile antenna is less than 1 ohm. IF YOU COULD, deliver a 100 watt signal to this there would be 100 amps of current and the Q would be so high that you wouldn't have enough bandwidth for the audio spectrum. Here is a example of a real short antenna. I tried to push some power into the 1KW tank circuit of my final once with the final turned OFF, by connecting the driver output to the output of the 1KW rig. The big tank capacitor ARCed over before I got 15 watts into it. John Coleman
Re: [AMRadio] antenna tuners transmision lines and more
> Actually there are a number of commercially manufactured tube > RF finals that DO indded use toroidal transformers. > Dentron, for one example - they made a number of linear amps > like that, and they were/are not alone. > The Alpha 374 had nothing but toroids. It might be remembered as the legal limit amp that ran for months with a brick on the key.. I bet most all Alphas are the same..Had 3 each 8874's..
RE: [AMRadio] antenna tuners transmision lines and more
Boy! You have to be real specific around here, HI I should have been more specific. I meant toroid wide band transformers not resonated and covering the entire HF spectrum with no tuning. I have seen toriods used in HF tube type equipment also but they still have tuning. I was speaking of rigs with no internal tuning for the final amps. Most modern solid state equipment is this way. This type of equipment that has no output tuning must have a specific non reactive load attached or it will not work as specified by the manufacture. This is where external tuning equipment is necessary because it is very difficult to get an antenna to be non reactive and represent a 50 ohm load. And should you achieve this then it would only be for a small range of frequencies. Where as, if you had a rig with adjustable output circuitry such as a Pi-Net with a loading and a plate tune knob then you would be able to match a much larger range of frequencies even though the VSWR on the coax line may be as high as 2:1. As Don, and perhaps another, have pointed out, these tube type rigs with build in load and tune controls are really just built in antenna tuners. As with any antenna tuner they have a limited range of Z and reactance that they can compensate for. It may be necessary to have another tuner external for matching balanced line etc. And as with many things there is specific type of circuits for external tuners that will do better jobs than others for a specific task. There are tuners specifically made that will match a balance line of 600 ohms to 6000 ohms to a 50 ohm source they may have a limit with in that as to the amount of reactance they can compensate for. Other tuners might be better at matching lower impedance loads. The circuitry needs to change for the best results. Now, there may be something that I have not seen that has tubes for output and yet no tuning on the final and that requires a specific load resistance for Z match as does the SS equipment. John -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mike Dorworth, K4XM Sent: Monday, April 24, 2006 11:37 AM To: Discussion of AM Radio Subject: Re: [AMRadio] antenna tuners transmision lines and more > Actually there are a number of commercially manufactured tube > RF finals that DO indded use toroidal transformers. > Dentron, for one example - they made a number of linear amps > like that, and they were/are not alone. > The Alpha 374 had nothing but toroids . It might be remembered as the legal limit amp that ran for months with a brick on the key.. I bet most all Alphas are the same..Had 3 each 8874's.. __ AMRadio mailing list Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net AMfone Website: http://www.amfone.net AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb
RE: [AMRadio] antenna tuners transmision lines and more
John said: "Now, there may be something that I have not seen that has tubes for output and yet no tuning on the final and that requires a specific load resistance for Z match as does the SS equipment." Jim Says, "Check out the Central Electronics 100V / 200V 100 watt transmitter with a pair of 6550's or the Central Electronics 600L linear amplifier with a grid driven 813. These are no tune tube circuits that work very well so long as the load is near 50 ohms resistive. These were way ahead of their time like standard front disc brakes on the Studebaker. Both companies disappeared in the 1960's too. Regards, Jim WD5JKO
RE: [AMRadio] antenna tuners transmision lines and more
> >The power may not be wasted very much in the tuner, BUT > >REFLECTED power goes back into the RF final and is disippated > >in the famil amplifier device(s) - at least many people have > >written articles for decades describing that marticular "myth" > >or so-called "FALSE STATEMENT." I am not so sure it is false > >though! > > That is a myth. Thanks - I stand corrected. I think I read that in some ham magazine years ago and it got stuck in my head! I can accept the idea that most wattmeters give false readings on FWD power too!
RE: [AMRadio] antenna tuners transmision lines and more
From: "John E. Coleman (ARS WA5BXO)" <[EMAIL PROTECTED]> I have seen toriods used in HF tube type equipment also but they still have tuning. I was speaking of rigs with no internal tuning for the final amps. Most modern solid state equipment is this way. This type of equipment that has no output tuning must have a specific non reactive load attached or it will not work as specified by the manufacture. This is where external tuning equipment is necessary because it is very difficult to get an antenna to be non reactive and represent a 50 ohm load. And should you achieve this then it would only be for a small range of frequencies. Where as, if you had a rig with adjustable output circuitry such as a Pi-Net with a loading and a plate tune knob then you would be able to match a much larger range of frequencies even though the VSWR on the coax line may be as high as 2:1. What it boils down to is that with classic tube type rigs, the rf tank circuit was built into the rig. With modern solid state rigs, the rf tank circuit comes as an external option that you have to pay extra for. I recall there was a Central Electronics rig that had a no-tune broadband output network with a tube type final. They sealed the whole thing in something like epoxy, and gave no technical data on how it worked. I recall reading an article in CQ or 73 Magazine about how someone unsuccessfully tried to disassemble one of the networks to find out how it worked, and ended up with "probably the only (Central Electronics rig) with a tuneable pi-network tank circuit. Don k4kyv
Re: [AMRadio] antenna tuners transmision lines and more
- Original Message - From: "Donald Chester" <[EMAIL PROTECTED]> > I recall there was a Central Electronics rig that had a no-tune broadband > output network with a tube type final. They sealed the whole thing in > something like epoxy, and gave no technical data on how it worked. Yes but it was a patented device and the patent number was shown. I sent for the patent disclosure and built the coil as presented. It worked perfectly and I made measurements that showed it's own impedance to be 25 ohms and it would easily match 25 to 100 ohms 2:1 SWR. Mine was for a single 813 final. As I recall the network was in some ceramic that was nearly impossible to open short of an A-Bomb and many wondered what was inside since no-tune was a mystery at that time.. Mike
