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
Topband: topband report from 4V1JB
Our plans for a 160m operation and CQWWCW entry were delayed due to supply issues and construction woes. THINGS ARE NOT EASY IN HAITI !!! We are very fortunate that we had any place to operate. We had only very low dipoles on the higher bands at the hotel/guesthouse. Thanks to the great kindness of Jean-Robert HH2JR (who is also famous for his efforts in the Haitian earthquake) we were offered the opportunity to use his nice station for the contest, and operate with the club callsign of 4V1FR. The last two days we worked on erecting the 160m antenna. We need to be thankful for three things, the kindness of HH2JR, the efforts to put up the antenna (including tower climbing and roof-climbing by an un-named old guy) and the excellent filtering ability of the Elecraft K3. We did not have time or space for a listening antenna, although with more time I would have tried. In the end we worked 180 stations on topband and had 3100 QSOs in the contest, which is not bad for a contest operation with only two ops. We aso had three lengthy power outages during which we got good exercise trying to start the generator. You probably already know that we were there on the top of every hour. We made a big effort on 160m because of the need. The antenna was an inverted Vee with one side folded back to the tower about 15 feet from the ground. The wire almost reached back to the tower. The other side went over a couple roofs and tied off in a neighboring property. It was an accomplishment to get this antenna erected and our host HH2JR was delighted to have a 160m antenna. The bad news is that we worked no EU stations, not a single one. We had 20 over 9 noise constantly...We did not have static crashes, just constant noise. One leg of the antenna was very close to a WIFI antenna. Not sure if that was the only culprit. I would like to know how we were being heard in EU...I have no reports. Our antenna described above and we used an Acom 1011 amplifier with about 750w output. Our best contact was with CN2AA. All other contacts were in the Caribbean area and North America. My goal in the future is to organize a dxpedition for topband operation only. We are looking for interested operators who love 160m. We know that contest weekends are not the best for DXing. We need a dedicated team of topband guys, not one guy without an RX antenna. But again, we need to thank HH2JR. Without his kind offer there would have been zero contacts on 160m last weekend. Thanks for all who called and wish that more of you could have been in the log. Please let me know if you would be interested in doing a 160m dxpedtion from Haiti. And please let me know how was our signal in EU compared to other stations. Thanks & 73 Dale - N3BNA _ 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
