Re: Topband: EZNEC 5.0 +
Hello Charlie & Paul, I'm using a single vertical wire Marconi T with a pair of 6 wire cages for the tophat. Each cage starts at a single point at the vertical top, and has 3 foot dowel spreaders at the far end. The reason is strictly to add more toploading in a smaller space. I needed another vertical to use in a phased array, but there were no suitable tree locations (I don't have any towers). So the vertical is suspended between two trees which were not far enough apart for resonance. EZNEC modelling provided the specifics. Besides, it looks vintage... Brian K8BHZ -Original Message- From: Charlie Cunningham Sent: Saturday, December 06, 2014 9:49 PM To: 'Paul Christensen' ; topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + Thanks for all the info and the memories, Paul!! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Paul Christensen Sent: Saturday, December 06, 2014 9:47 AM To: topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + Not sure that I can picture just what you are describing, Paul. Even though, I wasn't born until 1944, I've explored just about every type of antenna and I've modeled an awful lot of them. See the image in the link below: After rotating the image in your browser, note that the feed to the horizontal hat is fanned to form the vertical radiator. What looks like a complex antenna is nothing more than the classic T but with the horizontal hat spread out across six conductors. This was a very popular antenna during the spark-gap era. http://tinyurl.com/kdzkt2x The inverted L form of this antenna simply moved the center fan off to one side. This was typically done on smaller city lots as only one additional support was needed if you had a multi-story home. Both forms show up regularly on the pages of QST prior to about 1925. The famous 9ZN antenna was installed on the property of the Edgewater Beach Hotel in Chicago. After college, I lived across the street from the hotel when I was working for RKO Radio back in the mid '80s. What you see is really just a super wide conductor for the vertical radiator. This was not commonly used. The impact of the station was probably not so much from the vertical radiator as it was from attention paid to the extensive ground system. Here's a photo of the 9ZN antenna and ham shack taken around 1920. This is exactly where the Zenith brand began. https://musiccityvintageradio.files.wordpress.com/2011/03/house.jpg One of the more impressive antennas in the early '20s was that designed for 1BCG for the transatlantic tests. That antenna used a circular counterpoise as an elevated ground system. The vertical extends straight up from the shack roof. W2PA has assembled a nice page of information about the station and its operators. http://w2pa.net/HRH/crossings-iii-accolades/ Paul, W9AC --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Thanks for all the info and the memories, Paul!! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Paul Christensen Sent: Saturday, December 06, 2014 9:47 AM To: topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + > Not sure that I can picture just what you are describing, Paul. Even > though, I wasn't born until 1944, I've explored just about every type > of antenna and I've modeled an awful lot of them. See the image in the link below: After rotating the image in your browser, note that the feed to the horizontal hat is fanned to form the vertical radiator. What looks like a complex antenna is nothing more than the classic T but with the horizontal hat spread out across six conductors. This was a very popular antenna during the spark-gap era. http://tinyurl.com/kdzkt2x The inverted L form of this antenna simply moved the center fan off to one side. This was typically done on smaller city lots as only one additional support was needed if you had a multi-story home. Both forms show up regularly on the pages of QST prior to about 1925. The famous 9ZN antenna was installed on the property of the Edgewater Beach Hotel in Chicago. After college, I lived across the street from the hotel when I was working for RKO Radio back in the mid '80s. What you see is really just a super wide conductor for the vertical radiator. This was not commonly used. The impact of the station was probably not so much from the vertical radiator as it was from attention paid to the extensive ground system. Here's a photo of the 9ZN antenna and ham shack taken around 1920. This is exactly where the Zenith brand began. https://musiccityvintageradio.files.wordpress.com/2011/03/house.jpg One of the more impressive antennas in the early '20s was that designed for 1BCG for the transatlantic tests. That antenna used a circular counterpoise as an elevated ground system. The vertical extends straight up from the shack roof. W2PA has assembled a nice page of information about the station and its operators. http://w2pa.net/HRH/crossings-iii-accolades/ Paul, W9AC --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Thanks, Carl I suppose all those wires helped to increase bandwidth. Charlie K4OTV -Original Message- From: Carl [mailto:k...@jeremy.qozzy.com] Sent: Saturday, December 06, 2014 10:20 AM To: Charlie Cunningham; 'Paul Christensen'; 'topband' Subject: Re: Topband: EZNEC 5.0 + Charlie, visualize a straight horizontal wire wire between two tall points; then slanting to vertical wires coming down to the common feed point. The Titanic had a multi wire T horizontal and vertical fed in the center. Considering its daytime range of 200-400 miles and up to 2200 at night with about 500W radiated from a 5KW spark it was pretty effective on 600M. Carl KM1H - Original Message - From: "Charlie Cunningham" To: "'Paul Christensen'" ; "'topband'" Sent: Saturday, December 06, 2014 12:41 AM Subject: Re: Topband: EZNEC 5.0 + > Not sure that I can picture just what you are describing, Paul. Even > though, I wasn't born until 1944, I've explored just about every type of > antenna and I've modeled an awful lot of them. > > Of course the typical inverted L is just a monopole that is bent over at > the top to reduce the required support height, and an inverted L with > elevated radials is just a ground-plane antenna that is bent over at the > top and the Tee equivalents just replace the single top wire with equal > and opposite wires at the top to extend the monopole to resonant length. > The Tee version does eliminate the modest residual horizontal component in > the far field that occurs with the inverted L configuration. Of course > antenna current is still fundamentally important - that's what does the > radiation! I do still have a matched pair of RF ammeters around here, but > these days we accomplish the equivalent measurement by measuring forward > power with our SWR bridges. There's still a fundamental I-squared x R > relation between power and antenna current, where R is the radiation > resistance of the antenna + copper losses. So, it's all the same thing, > really. I can't come up with the name of the antenna that you are > describing, because I can't quite picture it. > > 73, > Charlie, K4OTV > > > -----Original Message- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Paul > Christensen > Sent: Friday, December 05, 2014 11:23 PM > To: topband > Subject: Re: Topband: EZNEC 5.0 + > >> "What did they call the teens to 20's antenna that had multiple feeds >> coming > down from one end of the flatop to the other?" > > Both the "T" and the fanned inverted L were popular on 200m in 1910-1920 > just as the single-wire Inverted L is today on 160m. Back then, ops were > obsessed with maximum antenna current but radiation resistance didn’t > enter into the discussions until the mid '20s. By the mid 20s when CW > took over, much less attention was paid to antenna current as a station > performance metric. > > During the spark era, ops would keep adding horizontal wires to the flat > top fans until the line current reached diminishing returns. We typically > see > 5-6 wires wide-spread in old station photos.Then, separate wires would > connect to the flat top and extended down a common point where it became a > single-wire feeder. > > Paul, W9AC > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2015.0.5577 / Virus Database: 4235/8690 - Release Date: 12/06/14 > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Not sure that I can picture just what you are describing, Paul. Even though, I wasn't born until 1944, I've explored just about every type of antenna and I've modeled an awful lot of them. See the image in the link below: After rotating the image in your browser, note that the feed to the horizontal hat is fanned to form the vertical radiator. What looks like a complex antenna is nothing more than the classic T but with the horizontal hat spread out across six conductors. This was a very popular antenna during the spark-gap era. http://tinyurl.com/kdzkt2x The inverted L form of this antenna simply moved the center fan off to one side. This was typically done on smaller city lots as only one additional support was needed if you had a multi-story home. Both forms show up regularly on the pages of QST prior to about 1925. The famous 9ZN antenna was installed on the property of the Edgewater Beach Hotel in Chicago. After college, I lived across the street from the hotel when I was working for RKO Radio back in the mid '80s. What you see is really just a super wide conductor for the vertical radiator. This was not commonly used. The impact of the station was probably not so much from the vertical radiator as it was from attention paid to the extensive ground system. Here's a photo of the 9ZN antenna and ham shack taken around 1920. This is exactly where the Zenith brand began. https://musiccityvintageradio.files.wordpress.com/2011/03/house.jpg One of the more impressive antennas in the early '20s was that designed for 1BCG for the transatlantic tests. That antenna used a circular counterpoise as an elevated ground system. The vertical extends straight up from the shack roof. W2PA has assembled a nice page of information about the station and its operators. http://w2pa.net/HRH/crossings-iii-accolades/ Paul, W9AC --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 + return loss and another question
Chuck, Next question: in the manual the ALT IMPEDANCE explantion uses a 4:1 transformer example, which I get. I've been toggling between RG213 50 ohm and rg6/u 75 ohm to observe differences, reasoning that if I use a 75 ohm feeder and get 2:0:1 or lower SWR values, the 50 ohm "system" would start (end) at the rig instead of the antenna feed point. I noted that the SWR bumped up a bit when I added a 120ft transmission line, which I would expect. I'm not sure what you are saying there, but it seems the usual "stuff" about SWR that trips people up may be confusing you. Unless you want to get into complex wave theory that takes a chapter of text to explain a simple concept, it is best to look at this a different way. If we were transmitting video or had very high speed digital systems, we would have to consider reflected waves. We have steady-state systems where levels change over many RF cycles, not pulse or extreme bandwidth systems. The real reason system performance changes with SWR is the impedance changes throughout the system. This impedance change causes voltages and currents throughout the system to change, and this causes losses to change. SWR or mismatch can change the loadline seen by the PA device(s), changing how the PA device works. You probably don't need to know any of that to answer your question. If you can ask a specific question, it should be easy to answer the question without confusing you. Are you asking how to best model 75 ohm transmission lines in EZNEC? If not, what are you trying to do with the model?? 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
>We can have 67% reflected power and still have nearly 100% of transmitter >power getting into the antenna and being radiated. Then could someone please explain why the manufacturers of ham, broadcast AM/FM/TV, and other transmitters specify the maximum SWR (e.g., minimum return loss) for the loads they may drive at full, rated output power (no foldback)? If "nearly 100%" of the r-f power output of such transmitters was radiated by the antenna system regardless its VSWR/return loss, what would be the need for such OEMs to specify a maximum load SWR? Easy. It has nothing to do with reflected waves reaching the PA device. "Reflected power", or SWR, can actually make a PA run cooler. The job of a tank circuit or output matching circuit is to establish a LOADLINE for the power amplifier device. This is found through a form of Fourier analysis of the time varying voltage and current at the output device, or through experimentation. This loadline is selected to provide either the best energy transfer from the device, the best linearity, or some other target goal or combination of goals. When the load mismatches the output impedance transformation design termination impedance, the PA load impedance deviates from optimum. As far as the PA stage goes, SWR really just indicates an impedance mismatch from ideal. The PA termination impedance change is transformed through the output matching to move the loadline. If the tank system can be readjusted to a new value, you can have a 50:1 feedline SWR and not hurt the PA system. The only limit is voltage and current rating of components up to the output device end of the matching system. But again, a mismatch from the impedance the tank was adjusted for simply changes the loadline seen by the PA device. Mismatch can make PA heat decrease, increase, or stay the same. It can make distortion increase, decrease, or stay the same. It is nothing other than a change in loadline to the PA device. http://www.w8ji.com/Vacuum_tube_amps.htm By the way, there is no source impedance to match in a typical PA. The PA device impedance is varying constantly through the RF cycle. With class B or shorter angles, the PA device is switching completely off for a portion of the cycle. The only "impedance" is loss loading of the system. This is why tank voltages on the anode of a tube can go ten or twenty times the DC supply voltages with certain termination impedances. http://www.w8ji.com/demonstation.htm _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: EZNEC 5.0 + return loss and another question
Thanks for your explanations Charlie es Tom. I guess return loss is the opposite of what it sounded like to me. At any rate, you've explained why it varies inversely with SWR. Next question: in the manual the ALT IMPEDANCE explantion uses a 4:1 transformer example, which I get. I've been toggling between RG213 50 ohm and rg6/u 75 ohm to observe differences, reasoning that if I use a 75 ohm feeder and get 2:0:1 or lower SWR values, the 50 ohm "system" would start (end) at the rig instead of the antenna feed point. I noted that the SWR bumped up a bit when I added a 120ft transmission line, which I would expect. Am I interpreting alt impedance feature and results correctly? I don't have a single piece of 50 ohm that long but have long pieces of brand new CATV rg6/u from a hamfest jackpot. In chapter six on Transmission Lines in Low Band DXing the suggestion is to use a half-wave section of 75 ohm to aid the match. I have enough rg6u and a 941E tuner if needed to do this. BTW this whole exercise is mostly intended as a lab session for me and a way to get into top band quickly with a temporary antenna. I expected before - and after looking at the FFT pattern have certainly confirmed - that a flattop half wave dipole at 50 feet over rocky ground is not going to work out as a DX antenna. But it might be good enough to allow me to NCS a Tuesday night follow-on cw net after my regular net on 7.117, z Tuesday nights. Hope to be in business by Stew Perry contest. 73, chuck -- de AB1VL NAQCC #6799 ab1vl.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
On Fri,12/5/2014 12:29 PM, Charles Yahrling wrote: Just getting started modelling and looking for answers to questions not found in manual so far. For example, what exactly is included in the Return Loss figure shown in the SWR window? Just ground reflection loss, total system loss, something else? Trying to understand why Return Loss is greater for lower SWR curve values. e.g see this when toggling between std and alt impedance. What is this suggesting, go with lower return loss or lower swr curve? An incomplete grasp of the fundamentals is admittedly likely here . So that's what you need to study. ARRL Handbook and ARRL Antenna Book. Those of us who understand have paid those dues. Now it's your turn to hit the books. :) Tough love. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Not sure that I can picture just what you are describing, Paul. Even though, I wasn't born until 1944, I've explored just about every type of antenna and I've modeled an awful lot of them. Of course the typical inverted L is just a monopole that is bent over at the top to reduce the required support height, and an inverted L with elevated radials is just a ground-plane antenna that is bent over at the top and the Tee equivalents just replace the single top wire with equal and opposite wires at the top to extend the monopole to resonant length. The Tee version does eliminate the modest residual horizontal component in the far field that occurs with the inverted L configuration. Of course antenna current is still fundamentally important - that's what does the radiation! I do still have a matched pair of RF ammeters around here, but these days we accomplish the equivalent measurement by measuring forward power with our SWR bridges. There's still a fundamental I-squared x R relation between power and antenna current, where R is the radiation resistance of the antenna + copper losses. So, it's all the same thing, really. I can't come up with the name of the antenna that you are describing, because I can't quite picture it. 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Paul Christensen Sent: Friday, December 05, 2014 11:23 PM To: topband Subject: Re: Topband: EZNEC 5.0 + > "What did they call the teens to 20's antenna that had multiple feeds > coming down from one end of the flatop to the other?" Both the "T" and the fanned inverted L were popular on 200m in 1910-1920 just as the single-wire Inverted L is today on 160m. Back then, ops were obsessed with maximum antenna current but radiation resistance didn’t enter into the discussions until the mid '20s. By the mid 20s when CW took over, much less attention was paid to antenna current as a station performance metric. During the spark era, ops would keep adding horizontal wires to the flat top fans until the line current reached diminishing returns. We typically see 5-6 wires wide-spread in old station photos.Then, separate wires would connect to the flat top and extended down a common point where it became a single-wire feeder. Paul, W9AC _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
"What did they call the teens to 20's antenna that had multiple feeds coming down from one end of the flatop to the other?" Both the "T" and the fanned inverted L were popular on 200m in 1910-1920 just as the single-wire Inverted L is today on 160m. Back then, ops were obsessed with maximum antenna current but radiation resistance didn’t enter into the discussions until the mid '20s. By the mid 20s when CW took over, much less attention was paid to antenna current as a station performance metric. During the spark era, ops would keep adding horizontal wires to the flat top fans until the line current reached diminishing returns. We typically see 5-6 wires wide-spread in old station photos.Then, separate wires would connect to the flat top and extended down a common point where it became a single-wire feeder. Paul, W9AC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Hello Paul, RE: Typically a transmitter will fold-back delivered power when its output Z is fixed (e.g., 50 or 70-ohm) and SWR exceeds some predetermined amount set by the manufacturer. This is typical of broadbanded solid-state amplifiers with a fixed output Z that use no output matching network. These transmitters are designed to work into just one line Z and hence a strict maximum SWR at the transmitter's output terminals. From my perspective/research/experience from nearly 40 years in the broadcast industry before I retired in 1999 -- including 15 yrs at RCA Broadcast, then 19 years at Harris Broadcast Division ... Normally the impedance at the active output elements (plates/collectors etc) of a transmitter is much lower than 50 or 75 ohms, so that it can drive a 50 or 75 ohm load connected to the transmitter output connector with good efficiency. If the net impedance at the output elements of the transmitter exactly matched the load impedance of the antenna system, only 50% of the available r-f output power would be dissipated by that antenna system. Broadcast/other transmitters using vacuum tubes often included adjustable matching components in the cabinet so that the transmitter safely could produce 100% of its maximum rated output power into a load SWR of 1.7:1, or so. But many of them also include(d) power foldback to protect the transmitter if the load SWR exceeded that 1.7:1 nominal value. Some solid-state broadcast transmitters do not include such matching components, and consequently their maximum load SWR for full rated ouput power is about 1:3:1 or so, and they fold back if load SWR exceeds that value. Rich http://rfry.org _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
The bad thing about high SWR in a high powered system are the resulting high voltage points and high current points generated by the forward and reflected waves. Those high voltages and current points can do a lot of damage to your equipment. 73 Lloyd - N9LB -Original Message- From: Topband [mailto:topband-boun...@contesting.com]On Behalf Of Charlie Cunningham Sent: Friday, December 05, 2014 6:30 PM To: 'Tom W8JI'; 'Charles Yahrling'; topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + Well, I would respectfully disagree with Tom, that "Return Loss" is confusing or ,misleading. It's just another way of looking at reflections that often makes more sense of is more useful. For example, many filters etc. are specified in terms of their input return loss, usually in a 50 ohm system,and engineers working in the lab with vector network analyzers measure most all input matches in terms of return loss. On a Smith Chart, return-loss is a radially scaled parameter, as is VSWR. The origin of the chart, at a perfect match would be the 1:1 VSWR point,or the infinite return loss point. Conversely, the perimeter of the chart corresponds to 0 return loss or infinite VSWR. EZNEC and network analyzers tend to express things in terms of return-loss, although VSWR is also available. For modeling in EZNEC and tuning or sweeping your antenna models,you want to MAXIMIZE return loss and MINIMIZE VSWR- it's the same thing. As an example to illustrate Tom's point. IF we fed a resonant 1/2 Wave dipole at its center, with 600 ohm open-wire line, the VSWR on the feedline would approach 10:1, but there would be almost no loss in the feedline and virtually 100% of the incident power would be radiated by the antenna. The challenge would be to match the transmitter to whatever values of R+JX presented themselves at the sending end of the line. Have fun with EZNEC! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Friday, December 05, 2014 4:40 PM To: Charles Yahrling; topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + Return loss is just another misleading confusing way to express SWR. Return loss, like percentage reflected power, does not indicate any type of loss. It just expresses SWR in a different form. We can have 10:1 SWR, which would be a 1.743 dB return or "mismatch" loss or 67% reflected power, and still have virtually no loss. We can have 67% reflected power and still have nearly 100% of transmitter power getting into the antenna and being radiated. The best advice is to ignore it all, and just use SWR for now. :) - Original Message - From: "Charles Yahrling" To: Sent: Friday, December 05, 2014 3:29 PM Subject: Topband: EZNEC 5.0 + > Just getting started modelling and looking for answers to questions not > found in manual so far. For example, what exactly is included in the > Return Loss figure shown in the SWR window? Just ground reflection loss, > total system loss, something else? Trying to understand why Return Loss > is > greater for lower SWR curve values. e.g see this when toggling between std > and alt impedance. What is this suggesting, go with lower return loss or > lower swr curve? > > An incomplete grasp of the fundamentals is admittedly likely here . > > 73, chuck > > > -- > de AB1VL > NAQCC #6799 > > ab1vl.com > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4794 / Virus Database: 4235/8686 - Release Date: 12/05/14 > _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Rich, It's an issue that's not usually seen in the broadcast engineering world where one frequency is transmitted for broadcast. Typically a transmitter will fold-back delivered power when its output Z is fixed (e.g., 50 or 70-ohm) and SWR exceeds some predetermined amount set by the manufacturer. This is typical of broadbanded solid-state amplifiers with a fixed output Z that use no output matching network. These transmitters are designed to work into just one line Z and hence a strict maximum SWR at the transmitter's output terminals. It's possible to recover and re-direct the reflected wave (created by the line to load mismatch) back to the load if a network is used to tune the line for reactance cancellation and match the output Z of the transmitter. The usefulness of this is highly dependent on line loss. In the ham's world where low-loss open and balanced feeders are often used, it's quite common to have a 20:1 line SWR, yet attain 90% or better transmission efficiency. Of course, as line loss increases, the ability to take advantage of this approach becomes less effective. By using a network directly after a solid state, fixed Z transmitter, the line Z can vary wildly, but the network just installed will manage the tuning and matching function to ensure the transmitter is matched into the network. Back to the broadcast world: early AM stations would use multi-conductor open feeders with no ATU at the vertical tower's base -- nor in cases of station's still using flat-top Marconi "T"s. For normal AM broadcast (but not C-QUAM stereo or IBOC), the entire tuning function is quite capably done at the transmitter even hundreds of feet away from the vertical. Line SWR is high, but it matters little as line loss is extremely low at MW. Of course with high SWR, voltage handling between conductors and insulator spacing needs to be well-managed. As directional systems became necessary along with increased use of coaxial lines, it meant that each tower needed its own ATU at the tower base to perform an exact line to feed Z match -- with all phasing conducted in a common phasor cabinet located near the transmitter -- a universal set-up we've seen used probably since the late '30s, maybe even earlier. Paul, W9AC -Original Message- From: Richard Fry Sent: Friday, December 05, 2014 6:54 PM To: topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + We can have 67% reflected power and still have nearly 100% of transmitter power getting into the antenna and being radiated. Then could someone please explain why the manufacturers of ham, broadcast AM/FM/TV, and other transmitters specify the maximum SWR (e.g., minimum return loss) for the loads they may drive at full, rated output power (no foldback)? If "nearly 100%" of the r-f power output of such transmitters was radiated by the antenna system regardless its VSWR/return loss, what would be the need for such OEMs to specify a maximum load SWR? R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Well, I would respectfully disagree with Tom, that "Return Loss" is confusing or ,misleading. It's just another way of looking at reflections that often makes more sense of is more useful. For example, many filters etc. are specified in terms of their input return loss, usually in a 50 ohm system,and engineers working in the lab with vector network analyzers measure most all input matches in terms of return loss. On a Smith Chart, return-loss is a radially scaled parameter, as is VSWR. The origin of the chart, at a perfect match would be the 1:1 VSWR point,or the infinite return loss point. Conversely, the perimeter of the chart corresponds to 0 return loss or infinite VSWR. EZNEC and network analyzers tend to express things in terms of return-loss, although VSWR is also available. For modeling in EZNEC and tuning or sweeping your antenna models,you want to MAXIMIZE return loss and MINIMIZE VSWR- it's the same thing. As an example to illustrate Tom's point. IF we fed a resonant 1/2 Wave dipole at its center, with 600 ohm open-wire line, the VSWR on the feedline would approach 10:1, but there would be almost no loss in the feedline and virtually 100% of the incident power would be radiated by the antenna. The challenge would be to match the transmitter to whatever values of R+JX presented themselves at the sending end of the line. Have fun with EZNEC! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Friday, December 05, 2014 4:40 PM To: Charles Yahrling; topband@contesting.com Subject: Re: Topband: EZNEC 5.0 + Return loss is just another misleading confusing way to express SWR. Return loss, like percentage reflected power, does not indicate any type of loss. It just expresses SWR in a different form. We can have 10:1 SWR, which would be a 1.743 dB return or "mismatch" loss or 67% reflected power, and still have virtually no loss. We can have 67% reflected power and still have nearly 100% of transmitter power getting into the antenna and being radiated. The best advice is to ignore it all, and just use SWR for now. :) - Original Message - From: "Charles Yahrling" To: Sent: Friday, December 05, 2014 3:29 PM Subject: Topband: EZNEC 5.0 + > Just getting started modelling and looking for answers to questions not > found in manual so far. For example, what exactly is included in the > Return Loss figure shown in the SWR window? Just ground reflection loss, > total system loss, something else? Trying to understand why Return Loss > is > greater for lower SWR curve values. e.g see this when toggling between std > and alt impedance. What is this suggesting, go with lower return loss or > lower swr curve? > > An incomplete grasp of the fundamentals is admittedly likely here . > > 73, chuck > > > -- > de AB1VL > NAQCC #6799 > > ab1vl.com > _ > Topband Reflector Archives - http://www.contesting.com/_topband > > > - > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4794 / Virus Database: 4235/8686 - Release Date: 12/05/14 > _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
We can have 67% reflected power and still have nearly 100% of transmitter power getting into the antenna and being radiated. Then could someone please explain why the manufacturers of ham, broadcast AM/FM/TV, and other transmitters specify the maximum SWR (e.g., minimum return loss) for the loads they may drive at full, rated output power (no foldback)? If "nearly 100%" of the r-f power output of such transmitters was radiated by the antenna system regardless its VSWR/return loss, what would be the need for such OEMs to specify a maximum load SWR? R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Hi, Chuck Well return loss is a transmission line term that is a measure of the reflection on the line. So a transmission line that is terminated in its characteristic impedance would have 0 reflection, or infinite return loss or 1.0:1 VSWR. Conversely if the line was lossless and terminated in an open or a short, 100% of the incident power would be reflected, resulting in 0dB return loss, or infinite VSWR. So you want to target the lowest VSWR - as close to 1.0:1 as possible. BTW, it can be shown in the general case, that minimum VSWR will occur at RESONANCE. Have fun with EZNEC, it's a wonderful, powerful, and easy to use program that have used over the years to model,design and build some wonderful "killer" antennas that have performed wonderfully! Have fun and keep learning! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Charles Yahrling Sent: Friday, December 05, 2014 3:29 PM To: topband@contesting.com Subject: Topband: EZNEC 5.0 + Just getting started modelling and looking for answers to questions not found in manual so far. For example, what exactly is included in the Return Loss figure shown in the SWR window? Just ground reflection loss, total system loss, something else? Trying to understand why Return Loss is greater for lower SWR curve values. e.g see this when toggling between std and alt impedance. What is this suggesting, go with lower return loss or lower swr curve? An incomplete grasp of the fundamentals is admittedly likely here . 73, chuck -- de AB1VL NAQCC #6799 ab1vl.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Return loss is just another misleading confusing way to express SWR. Return loss, like percentage reflected power, does not indicate any type of loss. It just expresses SWR in a different form. We can have 10:1 SWR, which would be a 1.743 dB return or "mismatch" loss or 67% reflected power, and still have virtually no loss. We can have 67% reflected power and still have nearly 100% of transmitter power getting into the antenna and being radiated. The best advice is to ignore it all, and just use SWR for now. :) - Original Message - From: "Charles Yahrling" To: Sent: Friday, December 05, 2014 3:29 PM Subject: Topband: EZNEC 5.0 + Just getting started modelling and looking for answers to questions not found in manual so far. For example, what exactly is included in the Return Loss figure shown in the SWR window? Just ground reflection loss, total system loss, something else? Trying to understand why Return Loss is greater for lower SWR curve values. e.g see this when toggling between std and alt impedance. What is this suggesting, go with lower return loss or lower swr curve? An incomplete grasp of the fundamentals is admittedly likely here . 73, chuck -- de AB1VL NAQCC #6799 ab1vl.com _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4794 / Virus Database: 4235/8686 - Release Date: 12/05/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: EZNEC 5.0 +
Chuck, SWR and return loss are related. Check these out: http://en.wikipedia.org/wiki/Return_loss http://www.minicircuits.com/app/DG03-111.pdf What are you modeling? 73, Mike www.w0btu.com On Fri, Dec 5, 2014 at 2:29 PM, Charles Yahrling wrote: > Just getting started modelling and looking for answers to questions not > found in manual so far. For example, what exactly is included in the > Return Loss figure shown in the SWR window? Just ground reflection loss, > total system loss, something else? Trying to understand why Return Loss is > greater for lower SWR curve values. e.g see this when toggling between std > and alt impedance. What is this suggesting, go with lower return loss or > lower swr curve? > > An incomplete grasp of the fundamentals is admittedly likely here . > > 73, chuck > > > -- > de AB1VL > NAQCC #6799 > > ab1vl.com > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: EZNEC 5.0 +
Just getting started modelling and looking for answers to questions not found in manual so far. For example, what exactly is included in the Return Loss figure shown in the SWR window? Just ground reflection loss, total system loss, something else? Trying to understand why Return Loss is greater for lower SWR curve values. e.g see this when toggling between std and alt impedance. What is this suggesting, go with lower return loss or lower swr curve? An incomplete grasp of the fundamentals is admittedly likely here . 73, chuck -- de AB1VL NAQCC #6799 ab1vl.com _ Topband Reflector Archives - http://www.contesting.com/_topband
