THE EFHWA, Too many grey areas, too much unknown.
I have been using recently a homebrew end fed half wave monobander, courtesy of PD7MAA, (A real gentleman) on both 20 and 40 metres (seperate),.. now Mr Steve Yates advises a 1 mtr counterpoise as well as many other learned minds do the same, yet my signal reports/performance has gone up immeasurably with a 1/4 single counterpoise, ie 16.5 0n 20 and 33 on 40 metres.
This seems to be hotly debated and i still have no concrete way forward as to this very Grey area,...All i can say for absolute certaincy is that the 1/4 wave counterpoise earth return is head and shoulders better than the 1 metre counterpoise so often advised?
Does anybody out there have any experience of A/B type comparisons?
Thank you for your time and listening, M6AWG, Mark.
Last edited by M6AWG; 04-08-2012 at 11:43 PM.
Originally Posted by M6AWG
You have made a antenna that you feel is better than 1 metre counterpoise version,
therefore from your point of view you have made a better mousetrap.
What does it matter to you that there are many unknowns with this design and plenty of debate
by those who have not achieved same for them selves? As far as I am concerned you are the expert as you have made one that works better, which makes you the expert as a bird in the hand is worth more than two in the bush. Oh, somebody may model it and swear that it should be a 1 metre counterpoise but until they make one to prove their point they are just talking heads. I assure you that when a final determination comes about there will be many hams who will state that they personaly knew that all the time!
Thank you, I wasn't expecting that unconventional reply. It just seems to me that with so many talented people and brilliant minds out there that this seems to me to be the one antenna counterpoise debate that nobody seems to state with any conviction as to wether it functions better with the shorter, longer or even no c/poise at all!
Thank you Art for taking time out to offer a left field scenario.
Have you ever heard anyone credible say that it actually performs better with a 1m counterpoise or no counterpoise at all or have you just heard that those things may be an adequate solution for an end fed half wave?
Originally Posted by M6AWG
A good low impedance RF ground will not hurt an EFHW. It's not necessary like it is for a quarter wave or critical like it is for a shorter, low radiation resistance antenna, but there's no reason why a 1m counterpoise would make a EFHW work better.
I suppose I do have sort of an A/B example: for a long time and still in the winter, my 40m antenna is very close to an end fed half wave supported by an 18m Spiderbeam pole. It happens to have a reasonably good radial system underneath it: 27 radials from 15 to 40 feet long out to the edges of my yard. This radial system is good enough that my 3m tall 40m vertical (http://www.n3ox.net/projects/n3oxflex) is within maybe 1-1.5dB of a quarter wave despite its low radiation resistance (about 5 ohms?). At any rate, it's a very good low impedance RF ground on 7MHz.
I would not have built this system if I only used an end fed half wave. I have this radial system because I've used various antennas on various bands; I run 80m and 160m (with a loading coil) on the big antenna as well. In order to facilitate lawn mowing I connected the matching box to the radials using an Anderson Powerpole, which works fine but it is a little easy to accidentally disconnect.
On 40m I don't really notice when it gets disconnected. The matching network has an aluminum baseplate maybe 45x60 cm (http://n3ox.net/projects/stepperswitch/networks_lg.jpg, 40m match in the lower right) and that's more than enough capacitance to ground (granted, it's capacitance to a ground that's overlaid with radials, but still, I don't even notice). On the rest of the bands, including 30m where the antenna is fairly high impedance, the SWR goes way out of whack and signals go down. On 80 and especially 160 where a good ground is needed, signals plummet. Some of this is bad match to the RX but some is just low efficiency from poor ground return. But on 40m, no problem. Maybe a tiny shift in the SWR but no worse than normal weather variations. No RF in the shack even with 500W to the antenna. So it doesn't really matter if I have the antenna ground current running through a few hundred ohms of reactance from the matching baseplate to ground or directly connected to a low impedance ground system. It barely changes anything. I haven't done a detailed gain/FS comparison because I don't want to run the antenna unplugged, nor have I measured the current on the coax shield in both configurations (I suppose I could do that easily but I do not have the antenna up anymore) but I certainly don't notice.
Now a 45x60cm plate a couple inches from the earth is significantly more counterpoise than a 1m wire. But in all cases whether or not a minimal counterpoise is adequate starts to touch on many criteria that have not a thing to do with electromagnetic theory. Cost, convenience and space all start to get mixed into the debate.
Furthermore, I think that there are very few if any real world situations in which a 1m counterpoise is adequate in the sense that it will actually work sufficiently to keep current off the coax shield. Any kind of matching that has a direct metallic connection of the counterpoise and coax shield to the antenna like stub matching or an autotransformer (the two I saw on PD7WWW's site) will result in all the counterpoise current flowing on the coax and none on a 1m counterpoise. In fact, I think the interwinding capacitance of real isolation transformers is probably enough to cause some current on the coax shield instead of such a small counterpoise. With an isolation transformer there's a better chance that the current won't flow predominantly on the coax shield, but there still could be some. With an isolation transformer I think there's a good chance that some kind of short "counterpoise" is useful for getting a match even if it's not handling all the return current.
But since there are many, many criteria by which people judge success especially for "compromise" antennas for restricted situations, it may be that coax-as-counterpoise is just fine for them. But maybe it wasn't for you for whatever reason. I don't have a good idea why your results were so dramatic: frankly I'm a little surprised. But you've made your antenna better and if you experiment with different lengths of counterpoise and main radiator, maybe you can get a better idea why the improvement happened. It may be that you really needed a 1/4 wave counterpoise to keep the current off the coax and you had a particularly pathological situation where the coax currents were causing lots of loss. I find that plausible.
I don't think, however, that anyone is saying a 1m counterpoise or no counterpoise is better for electrical reasons: it's not. It may be better for convenience but a very low impedance RF ground will not hurt an end fed half wave and it could help especially when coax currents could be unusually damaging to performance. That depends on so many specifics of your installation that you are the only one who can figure out what matters and what doesn't there. Does your transmission/reception with a 1m counterpoise change when you move the feedline around?
Thank you Dan for all the time and effort to put together your lengthy explanations. No, all is stable re the installation, but because I am only allowed 10 watts re my licence I get to, let's say, get to feel when my antenna is working very well as opposed to the guy up the road blasting everybody out of site with his linear. My signal reports have definitely improved with the 1/4 wave c/poise and my SWR has lowered too, but I'm not clever or technical enough to know why this has happened? I have a choke on my end-Feds with recommended rg58 lengths re the ARRL handbook. I work stealth from a first floor balcony flat with 28 gauge wire out to two distant trees, one takes my 20 metre and the other tree takes the 40 metre end fed. They are both working very well for me, but of course if I can tweak and improve things I will strive to do this via some of the much more technically minded than I on this forum,
Thank you Sir, Mark, M6AWG
All that matters is, are you happy with your antenna ? If you are, excellent. Just leave it alone, no matter what anyone says if you are happy, that's OK
I just took a quick peek on the PD7MAA website, and I do note that he does use a Coaxial Stub to match the antenna. I would not do that, as along that line the losses will be high (high SWR). For a matching stub, ladder line / wireman should have less losses. Or use a parallel tuned circuit, as AA5TB does. On the counterpoise, if I understand the data correctly on Steve's site, the 0,05 lambda counterpoise gives the antenne an purely ohmic impedance. (as does an 0,47 lambda one). I suppose that is why he does use that length.
What you could do is put the 1 meter long counterpoise on and compare it's performance. That's part of being a radio amateur, you get to experiment. Find out the facts and at that point you can either tell the other "experts" they are wrong or they are right. Either way you're the one that proved it. The one that works the best is the one you would use.
It might be said that a 1 meter counterpoise seems a bit short to be effective but, hey, I could be wrong.
Get back with us and tell us what happened with your experiment.
That is not a coaxial stub for matching in the sense you mean it. He copied my EndFedz design of using a length of coax as a coaxial capacitor in an L match. Typical matchbox loss is well under -0.3dB.
Originally Posted by LX2GT
I am puzzled about where you would hang a counterpoise on an end fed halfwave.
I am thinking it is a Zepp config, and where would you put a counterpoise (one meter long seems silly and insignificant) ?
Would the counterpoise go on the un-connected side of the ladder line at the top ?
Could you connect it to the tuner and dangle it under the op's desk ?
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