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
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
Hmmm, TMC TAC1 tuner specifies 80% efficiency. So at least in this case, 20% is lost. ftp://bama.edebris.com/bama/tmc/tac1/pages/tac1_04.jpg Apparently it gets worse as the frequency climbs up beyond 18 Mc I suspect the same is true for the johnson boxes that also use air coils. de KA4JVY Mark 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 compensation for them. But with solid state rigs and no internal tuning it would be an near necessity to have an external tuner if nothing more than a small PI-Net tuner such as the one I had from MFJ Having to do with the conservation of energy laws. Here are some facts. 1. High quality capacitors (especially air 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
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
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 compensation for them. But with solid state rigs and no internal tuning it would be an near necessity to have an external tuner if nothing more than a small PI-Net tuner such as the one I had from MFJ Having to do with the conservation of energy laws. Here are some facts. 1. High quality capacitors (especially air or vacuum type with good
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 compensation for them. But with solid state
RE: [AMRadio] antenna tuners transmision lines and more
Some of these MYTHS may actually be myths about myths. 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. When we speak of SWR, we are actually measuring VSWR in most cases, i.e. VOLTAGE standing wave ration - not current. Although they are related of course. 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! 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
