The QRP guys do have some good “stuff”. However commercial availability does not mean something is really good or even good.
For an example I refer you to the "Joystick "antenna once advertised in the RSGB magazine and elsewhere… As a young naive fella I bought one based on the glowing testimonials. Complete snake oil. Old hands warned me to buy something else but I wanted to believe. There are still people out there that think it might have some magic as a Google will show.
That said if you are wedded to the end fed concept then use it. Nothing I say is likely to change this but you should not think it isn’t a compromise.
Probably you will never agree with me but yes it is true. Think it through.
I put up a squid pole and unreel a quarter wave for the lowest band I want to use on each side. Half the length to keep out of the trees as compared to a full halfwave held up at the end.
If you suspend your wire in the centre the installations are equal.
I have deployed on summits where the trees were 10 m saplings 2 m apart so this in not armchair theory.
“Usually” because relatively few contacts are on the noise level, and if your antenna plus rig can detect the background noise then that 3dB doesn’t matter.
Too many over the last few days have been at the (high local) noise level when I’ve been on a summit. Not all summits are quiet Brian.
Are we not at 100 posts yet so this thread will close? (please).
I think a a couple of people have pointed out that it’s difficult to get the “ideal” antenna to a summit, have it weigh next to nothing, set up in no space at all (because the siummit is busy) and be directional to filter out noise and QRM - so we will always end up with a compromise to try and fit as many of our needs as we can. It can never be perfect. “even a bad antenna is better than no antenna at all” - most times anyway.
I’ve been lucky in that respect, I’ve never activated a really noisy summit (touch wood!) - but I would guess that if the noise level is that high a few dB loss in the antenna won’t matter, a more efficient antenna would bring in more of the noise as well as more of the signal.
Cheers for that Ron. That is one the best hand waves I’ve seen in a long time and I do offer you “respect dude” for going for it: respect
I’ve pointed people at the AA5TB site in the past and used his ideas myself until I left the matchbox on Knock of Crief or Torlum Hill some years back.
I have no deep grasp of antenna theory, I just use whatever works. However, one reason I use an endfed is that it requires no coax. The 10m of RG174 that comes with a SOTABEAMS 4 band linked dipole contributes 1.2 db loss on 20m (according to DXWire), so the true difference between that and an endfed is only 1.8 db (rising to 2.1 db at 80m). That said, there is nothing like a nice pile-up, so I am not totally sold on the “it’ll get you 4 contacts” mentality. When I do an activation with OE6LKG, we like to take his 4 band dipole and a 50w linear (no atu needed). Personally, I find a 10m mast, feeder and wire to be more difficult to set up on a wooded summit than an endfed, as the legs must be fairly evenly spread out to get the SWR down. Whereas, a Fuchskreis will tune up in all kinds of orientations. When I’m multi-day trekking, a 600g antenna and 1.5kg mast are out of the question, and 2db difference is irrelevant to me. Then, of course, there is the excellent out of band rejection provided by a Fuchskreis, on a noisy summit the difference over a normal dipole can be huge (to my ears anyway). OK, a Fuchskreis is a not quite the same as the impedance matched endfed that is the subject of this thread.
de OE6FEG / M0FEU
Matt
I built mine this weekend and tested it with less than great results. For the sake of testing, I tried it with a 28.8’ radiator on 20m. I could not get swr lower than 5:1. I figured maybe I’d wound the toroid incorrectly (or not got the enamel off the wire etc) so I redid it. Results were better but still not acceptable – 4:1 at best.
I’m guessing the 12’ of coax I am running isn’t providing enough braid to act as a counterpoise. They don’t provide any specs as to what they tested with, so I emailed. Their response: 25’. That’s not going to work for what I have in mind unfortunately (tiny ultralight kit). Back to the drawing board.
The name is really bad. It’s not no-tune because you need to get the length of wire correct or “tuned” as we say.
You need to measure just what you are seeing or you’ll never know what’s needed to make it better.
Mine used the same ratio (3T : 24T 1 : 8 = 64x impedance transform) and a Polyvaricon on the secondary. I followed AA5TB’s design and tuned mine the same… against a fixed resistor to get the tune point then replace with the radiator wire and trim get lowest SWR without adjusting the capcitor. 5m of radiator worked a dream(*) in that I could have 5m of vertical radiator, matchbox on the ground and a 1m counterpoise wire + 2m of RG58 to the 817. For whatever efficiency it had, I could work most of what I heard on 10/12m with it. Most failures were the problem of busting a pileup with 5W when people were running, shall we say, a bit more power
(*) for whatever definition of dream you want SWR 1blob or less on 10/12/15m and plenty of decent contacts worked (W, VE, PY, etc.). Efficiency? Who knows. There didn’t seem to be RF all over the 817 or mic or key and I could move them about and the SWR was constant.
Thanks Andy. I should have noted that I did attempt to tune the radiator length. Up to a foot in either direction both iterations, and those numbers were the best I could get.
One thing that is dawning on me is that even with a “no tune” setup (which has been tuned before hand) I am going to want at least some way to confirm swr hasn’t changed because of a bad connector, odd deployment etc. Unless I build one of Martin’s swr led boards into the ATS (possible!) that means carrying a little bridge/swr meter at least. And if I do that, I might as well carry one of the tiny tuners with swr indicators (emtech etc). And if I carry a tiny tuner, then I might as well use the tiny end fed wire setup I’ve been using with the kx2.
Today I made two transformers with ft114-43 and connected them back to back and found out that almost half of the power is lost (as heat) indicating almost 1.5dB per transformer.
Of course this was very simple measurement using two power meters and dummy load and it does not tell the real thing at all.
While trying to figure this out and wondering if I my core materials are really what they should be, I ran into this http://w7zoi.net/xfmrsefhw.html
Just wondering if anyone else has measured these famous efhw transformers with diffirent core materials? Oh yes, I know it is only one dB, but thats not the point here.
In the interests of adding some more knowledge to the discussion, Owen Duffy has a series of articles on the subject of EFHW transformers. Here’s his most recent work regarding a transformer identical to the commercial version in question: FT82-43 matching transformer for an EFHW – owenduffy.net
Short answer, the efficiency at 3.5 Mhz for this transformer is calculated to be ~65%. There are also some suggestions on how to begin improving the efficiency. Mr. Duffy also presents a different design for an 80-20m EFHW transformer with <10% core losses in another article: End Fed Half Wave matching transformer – 80-20m – owenduffy.net
Hi Joe, I just built one of these, this weekend. I lost the capacitor that came with it, so used a lower-value one I had. I cut the wire a bit longer than recommended, expecting to trim it down. I threw it up in the back yard, and had around 1.1-1.5:1 SWR across the band (approximately - that’s just the meter on my FT-817). That was direct-feed, no coax.
On my MTR-3B, I use a short (8-inch) RCA-BNC cable. It performs well there, too. To avoid unknown high-SWR situations there, I use the QRPGuys SWR indicator kit.
Thanks Rex. I think the issue I was having was related to an overly short radiator. I haven’t tried it with closer to an actual 1/2 wave length to start.
Btw, thanks for the QSO on Eight Dollar Mt. last week. I recognized your call when I was transcribing logs later that evening.
Fleshing out the data a bit, those wanting to experiment with this tuner might use the following chart as a jumping off point. It was derived using the ferrite core inductor calculator, also available on Owen’s website: Calculate ferrite cored inductor (from Al) . Keep in mind that secondary turns would have to be adjusted to maintain the 1:8 turns ratio, and that the capacitance would likely also need to be adjusted. This chart was generated only for the FT82-43 core and should not be used for other sizes or types.
Keep in mind that this will only affect the core losses and that other losses may occur elsewhere in the antenna system.
I don’t have problems using a tuner. I built this one a few years ago and tunes 40-30-20 (my main op bands) just fine. This baby is small and attached directly to the rig. I could have saved a few oz. by not including the LED/SWR indicating circuit since I just tune for peak audio and finish up using the SWR meter on the rig…fast and easy. Set up time is easy too.
