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Antenna at p. 95 of April QST?
Joe Cro N3IBX says his "big antenna" is resonant from 1500 kHz to 46
mHz. It is a military inverted-V, 110 ft. long total, with each end terminated in a 150 ohm resistor driven into the ground, center fed through a 9:1 balun. Assuming this is not an April 1 joke: (1) What are the drawbacks to this antenna? (2) What is the feedline? (3) Is there any more information about this type of antenna? (4) What is the point of burying the resistor, rather than one lead? Ken KC2JDY Ken (to reply via email remove "zz" from address) |
I haven't read the article, but I expect the word 'resonant' is
incorrectly used. Any antenna terminated with real resistors into the ground is generally a traveling wave non resonant antenna. In addition to radiating some of the RF it also wastes some of the RF in the two load resistors. It should work but not as well as a 110 foot inverted vee, open wire feeders and a tuner. Deacon Dave, W1MCE Ken wrote: Joe Cro N3IBX says his "big antenna" is resonant from 1500 kHz to 46 mHz. It is a military inverted-V, 110 ft. long total, with each end terminated in a 150 ohm resistor driven into the ground, center fed through a 9:1 balun. Assuming this is not an April 1 joke: (1) What are the drawbacks to this antenna? (2) What is the feedline? (3) Is there any more information about this type of antenna? (4) What is the point of burying the resistor, rather than one lead? Ken KC2JDY Ken (to reply via email remove "zz" from address) |
Ken wrote:
Joe Cro N3IBX says his "big antenna" is resonant from 1500 kHz to 46 mHz. He's defining "resonant" as no reflections. Instead of a standing-wave antenna, he is sacrificing half his power (or more) in the resistors to avoid reflections and turning the antenna into a traveling-wave antenna. It is a military inverted-V, 110 ft. long total, with each end terminated in a 150 ohm resistor driven into the ground, center fed through a 9:1 balun. Assuming this is not an April 1 joke: It's somewhat like a terminated-V antenna, described in the ARRL Antenna Book. (1) What are the drawbacks to this antenna? He is losing at least half his power in the resistors. Wouldn't you rather radiate that power? I go to great lengths to obtain an extra 1 dB. (2) What is the feedline? With a 9:1 balun, it can be coax since there are so few reflections. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Cecil Moore" wrote in message ... He is losing at least half his power in the resistors. Wouldn't you rather radiate that power? I go to great lengths to obtain an extra 1 dB. If I remember my traveling wave antenna theory, he wouldn't necessarily be loosing 3 dB in the resistors. At higher frequencies more of the power radiates before it gets to the loads, does it not? Jim N8EE |
On Thu, 15 Apr 2004 11:34:21 -0400, "JLB"
wrote: If I remember my traveling wave antenna theory, he wouldn't necessarily be loosing 3 dB in the resistors. At higher frequencies more of the power radiates before it gets to the loads, does it not? Jim N8EE Hi Jim, You are right (losing - unless it has diarrhea). What is described is a vertical, half Rhombic, a Military application for many years. This report appears to be about a design from yet another "inventor" who has "discovered" something that confounds the experts. The original poster asked for comments, especially about the resistor (the difference between shorting it and loading it) however, nothing is said about ground. Both of the resistors will require radials, however, there seem to be more specifics missing than that. In other words, what is the leg angle subtended at the fed point? Why not simply feed one end and terminate the other? Seems like a pain to elevate the feed point without some analysis showing why - but then it appears the column was painfully shy of anything technical beyond carpenter scaling. 73's Richard Clark, KB7QHC |
JLB wrote:
"Cecil Moore" wrote: He is losing at least half his power in the resistors. Wouldn't you rather radiate that power? I go to great lengths to obtain an extra 1 dB. If I remember my traveling wave antenna theory, he wouldn't necessarily be loosing 3 dB in the resistors. At higher frequencies more of the power radiates before it gets to the loads, does it not? Yes, "more" but not near 100%. A multi-wavelength terminated rhombic loses its reverse radiated lobes and along with them, quite a bit of power. Even on 10m, 110 ft. is only 3 wavelengths long. Averaged over all of HF, I'll bet that antenna loses close to half of its power in the resistors, assuming all reflections have been eliminated by the resistors. -- 73, Cecil http://www.qsl.net/w5dxp |
"Richard Clark" wrote in message ... You are right (losing - unless it has diarrhea). What is described is a vertical, half Rhombic, a Military application for many years. This report appears to be about a design from yet another "inventor" who has "discovered" something that confounds the experts. Dick, I challenge any antenna 'inventor' to invent an antenna that is not described in Kraus' book, at least at the fundamental theory level! Haven't seen one yet and I've been reading QST for over 30 years (not to mention my dad's collection that goes back to 1942). By the way, I 'invented' an interesting antenna several years ago, which I call the half-quad. The best way to describe it is dto picture a diamond shape quad, fed at the side corner, half buried in the ground. Shows some interesting patterns on the good ol' AO program. I came up with a three element version with one feed point (center element). You can change directions by switching a capacitor or inductor in and out of the two 'outside' elements. It didn't use terminating resistors. I couldn't get a multiband version to work. (and, no, I haven't built it yet) Jim N8EE (and yes, I qualify for the OT club but don't want to admit it quite yet). |
If I understand your description correctly, I'd be highly suspicious of
the results from AO or any other MININEC-based program because of the antenna's relatively low height. I recommend that you model the antenna with an NEC-2 based program using the Sommerfeld ground model (called "high-accuracy" ground in EZNEC) -- otherwise you might be pretty disappointed when you actually build it. Be sure to make note of the strength of the pattern as well as the shape of the NEC-2 program results, unless you're using the antenna only for receiving. Roy Lewallen, W7EL JLB wrote: . . . By the way, I 'invented' an interesting antenna several years ago, which I call the half-quad. The best way to describe it is dto picture a diamond shape quad, fed at the side corner, half buried in the ground. Shows some interesting patterns on the good ol' AO program. I came up with a three element version with one feed point (center element). You can change directions by switching a capacitor or inductor in and out of the two 'outside' elements. It didn't use terminating resistors. I couldn't get a multiband version to work. (and, no, I haven't built it yet) Jim N8EE (and yes, I qualify for the OT club but don't want to admit it quite yet). |
After investigating a large set of traveling wave antennas (not
Beverage) I think that the smallest amount of power dissipated in the terminating resistance was about 2 db. Mind, these were antennas with useful lengths and angles. It is likely that a rhombic with very long leg lengths would dissipate even less in its termination resistance. For amusement, I will have a look some time. One needs a lot of segments to simulate a three wire, ten wavelength rhombic! The antenna in question can be a useful expedient in exigent circumstances. Nice to hear from N8EE, another of Kraus' boys. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "JLB" wrote in message ... If I remember my traveling wave antenna theory, he wouldn't necessarily be loosing 3 dB in the resistors. At higher frequencies more of the power radiates before it gets to the loads, does it not? Jim N8EE |
J. McLaughlin wrote:
After investigating a large set of traveling wave antennas (not Beverage) I think that the smallest amount of power dissipated in the terminating resistance was about 2 db. Mind, these were antennas with useful lengths and angles. It is likely that a rhombic with very long leg lengths would dissipate even less in its termination resistance. Well, remember the posting that kicked off this discussion was about the following very short traveling-wave antenna: "It is a military inverted-V, 110 ft. long total, with each end terminated in a 150 ohm resistor driven into the ground, center fed through a 9:1 balun." A 110 ft. center-fed inverted-V is certainly going to have extensive losses in the resistors on most HF bands. After all, it is less than 1/2WL long on 75m and only 3 wavelengths long on 10m. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"J. McLaughlin" wrote in message ... Nice to hear from N8EE, another of Kraus' boys. 73 Mac N8TT Please explain. Do you mean that I have read Kraus' book, or that I was one of his students? (Which would be correct on both counts.) Nice to hear from another N by 2 callsign. Not very many of us around, it seems. Jim N8EE |
Nice to hear from another N by 2 callsign. Not very many of us around, it seems. Jim N8EE One more - Howdy from N2EE making noise in contests as flagship of Nikola Tesla RC, breaking records, exploring the frontiers of ocean fronts. Yuri da keykeeper of N2EE and NT1E (Nikola Tesla #1 Engineer) considered it to be my own call, but settled for the part of my old OK3BU |
J. McLaughlin wrote:
After investigating a large set of traveling wave antennas (not Beverage) I think that the smallest amount of power dissipated in the terminating resistance was about 2 db. Just modeled the subject antenna as well as I can. Without the termination resistors, the antenna has a gain of +6 dBi on 3.8 MHz. With the termination resistors, according to EZNEC, the gain drops to -10 dBi, a difference of 16 dB. -- 73, Cecil http://www.qsl.net/w5dxp |
That might not be a fair comparison, since the pattern might be quite
different with and without the resistors. To determine what fraction of the applied power is dissipated in the resistors, simply click the Load Dat button. Roy Lewallen, W7EL Cecil Moore wrote: J. McLaughlin wrote: After investigating a large set of traveling wave antennas (not Beverage) I think that the smallest amount of power dissipated in the terminating resistance was about 2 db. Just modeled the subject antenna as well as I can. Without the termination resistors, the antenna has a gain of +6 dBi on 3.8 MHz. With the termination resistors, according to EZNEC, the gain drops to -10 dBi, a difference of 16 dB. -- 73, Cecil http://www.qsl.net/w5dxp |
Roy Lewallen wrote:
That might not be a fair comparison, since the pattern might be quite different with and without the resistors. To determine what fraction of the applied power is dissipated in the resistors, simply click the Load Dat button. Well, the shape of the pattern looks the same. The Load Dat function produces 3015 watts into the antenna (high feedpoint impedance) and 1399 watts dissipated in each resistor. That's 217 watts not dissipated in the resistors out of 3015 watts into the antenna for an efficiency of about 7.2%, in the neighborhood of a mobile antenna on 75m. -- 73, Cecil http://www.qsl.net/w5dxp |
Cecil Moore wrote:
J. McLaughlin wrote: After investigating a large set of traveling wave antennas (not Beverage) I think that the smallest amount of power dissipated in the terminating resistance was about 2 db. Just modeled the subject antenna as well as I can. Without the termination resistors, the antenna has a gain of +6 dBi on 3.8 MHz. With the termination resistors, according to EZNEC, the gain drops to -10 dBi, a difference of 16 dB. -- 73, Cecil http://www.qsl.net/w5dxp The antenna described in this thread has been utilized by the military for simple, easy to erect and fairly inexpensive field use. I don't think that you will get any argument from anyone that a resistance terminated antenna is not as efficient as a tuned dipole. The benefit one receives from using a resistance terminated antenna is the lack of having to use an antenna tuner (another misnomer) when operating off resonance. I, personally, use a B&W folded resistance terminated antenna. This antenna is far from efficient but I can make great changes in operating frequency with out having to worry about matching the final circuit to the antenna. I would like to have a tuned dipole for each band/subband but have neither the room nor the desire to do so. Now if you go to the receiver and look at the signal strength meter, s-meter, you will see that 16db is only about 1 to 1 1/2 s units. In that a receiver can differentiate a signal down to a very small value the loss is of only academic interest, except to the purists. Dave WD9BDZ |
Oh my!
If you had a real E-mail address, I would have replied off-list. I am not sure what is the first to go as we age, but you have forgotten that we were both grad students of JDK. We have also both read his book! 73 Mac N8TT -- J. Mc Laughlin - Michigan USA Home: "JLB" wrote in message ... "J. McLaughlin" wrote in message ... Nice to hear from N8EE, another of Kraus' boys. 73 Mac N8TT Please explain. Do you mean that I have read Kraus' book, or that I was one of his students? (Which would be correct on both counts.) Nice to hear from another N by 2 callsign. Not very many of us around, it seems. Jim N8EE |
The antenna described in this thread has been utilized by the military
for simple, easy to erect and fairly inexpensive field use. Yes that is very true. However, what the military needs, and what us hams are trying to do is not that similar. What I would like as a ham is 100% of my rf radiated, especially when I am mobile. The military wants to communicate, and they don't care how the efficiency of the antenna system factors in to all this. In an old textbook of mine, the military wanted an automatic antenna tuner that would match 20KW to a 35' whip 2-30 MHZ. At 2MHZ the whip was very inefficient, and probably glowed in the dark. But they could communicate by the brute force method. I guess it depends on whether your goal is just to communicate, or communicate the most efficient way. 73 Gary N4AST |
On Fri, 16 Apr 2004 17:48:43 -0500, "David G. Nagel"
wrote: Now if you go to the receiver and look at the signal strength meter, s-meter, you will see that 16db is only about 1 to 1 1/2 s units. In that a receiver can differentiate a signal down to a very small value the loss is of only academic interest, except to the purists. Have you ever check the calibration of your S-meter? I have never found one that was 6dB per S-unit. Most seem to be around 3½-dB. Using that yard stick 16 dB is 4½ S-units. Many would consider that subatantial. Danny K6MHE |
David G. Nagel wrote:
I would like to have a tuned dipole for each band/subband but have neither the room nor the desire to do so. Now if you go to the receiver and look at the signal strength meter, s-meter, you will see that 16db is only about 1 to 1 1/2 s units. In that a receiver can differentiate a signal down to a very small value the loss is of only academic interest, except to the purists. Dave WD9BDZ A hundred bucks says you haven't checked your rig's S-meter response to two signals accurately measured as 16 dB different. 16 dB is the approximate gain of a 23 element Yagi having a 6.5 wavelength long boom (that's about 450 feet at 14 MHz), compared to a dipole. Only "Kurt Sterba" and a few others believe this amount of gain is insignificant. Roy Lewallen, W7EL |
David G. Nagel wrote:
I would like to have a tuned dipole for each band/subband but have neither the room nor the desire to do so. Now if you go to the receiver and look at the signal strength meter, s-meter, you will see that 16db is only about 1 to 1 1/2 s units. In that a receiver can differentiate a signal down to a very small value the loss is of only academic interest, except to the purists. Well, the average ham receiver's S-units are more like 4-5 dB steps. Even with the "standard" 6 dB per S-unit, 16 dB is about 2.7 S-units. I guess there are a lot of purist hams, me included. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I challenge any antenna 'inventor' to invent an antenna that is not
described in Kraus' book, at least at the fundamental theory level! Which addition? 73, Chip N1IR |
Here's a helpful hint on the (ohmic) loss: what is the power rating of the
resistor (and is it wirewound?) and what is the rated input power at the feed? Obviously there are multiple current maxima at the high end of HF That would seem to count for something:-) Graph the mismatch loss vs ohmic loss over the entire passband, then plot the peak gain compared to a (dipole of the same total height)--and then tell us this antenna doesn't work:-) Key question: what problem was this antenna solving? I bet that a 110 ft inverted V--unterminated and ungrounded --was far worse in solving the problem as posed. 73, Chip N1IR |
Which addition?
I hope some got the pun...for those who didn't...'which edition'? --C |
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