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This project is far enough along, I figured I'd post a photo. It's an EFHW, 40M, which will have a capacitor compensation stuck at about 25 feet on the wire.

The frame is made from 1/8" acetal stock, because it's what was handy. I wound the transformer as a 56:1 autotransformer. Yeah, I didn't leave enough room from the wire connector to the first strain relief hole, and that's bugging me enough that I'll probably use just 2 of them. :-P And, I need to get a longer #6 screw for the ground, for connecting the counterpoise wire. Every radio project requires at least one trip to the hardware store. Antenna connection is a BNC.

Very nice work Jed! I’m curious — what does the capacitor compensation do?

73,

Mark
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Mark Ehr | K0EHR

VP, 285 Tech Connect Radio Club
Littleton, Colorado

k0ehr@...
Check out my ham radio blog:

On Tue, 23 May 2023 19:17:24 -0700
Mark Ehr | K0EHR wrote:

Very nice work Jed! I’m curious — what does the capacitor compensation do?

The 40, 20, 15, and 10 bands don't actually line up with each other nicely
at 2X, 3X, and 4X the 40M frequencies. So, adding in some other components
will help bring the low point of the SWR curve for each band a little
closer to the band center. For example, you almost always see a capacitor
across the center and ground at the feedpoint side of the transformer,
which is supposed to help with 10M.

A capacitor in series in the wire will electrically shorten the wire,
however, the effect will vary with frequency, and possibly some other
factors which I don't understand.

In this particular case, the capacitor has more effect at 40M, and
generally less on the other bands. This is because capacitive reactance is
inversely proportional to frequency.

It's also possible to compensate a wire antenna using a coil, and it works
by electrically lengthening the wire, and again, it's frequency dependent.

Long discussion at QRZ:


--
Jed - KD0YMG -
"... we have done as much with wireless telegraphy as is likely
to be done."; Sir William Preece, 1891

Update! Well, not a lot to report - as usual, other things keep coming up and taking time, and I also find little things I hadn't thought of.

The counterpoise: the plan is to use a choke on the feedline at the feedpoint, and a 0.7 x wavelength counterpoise, based on information at QRZ and elsewhere. Part of that is that I think it'll be possible to refine the tuning by changing the length of the counterpoise. And I had forgotten to consider keeping the counterpoise elevated. I think that's the best approach, based on my experience with the antenna.(Link to the Wayback Machine, because it seems now that Google Sites, or maybe Budd, has required a Google login to load the page.) BTW, if anyone wants the PDF for the plans, I made a some minor edits for readability and clarity - just shoot me an e-mail. So, on the counterpoise, in the short term, I suppose I'll tie a couple bamboo garden sticks into a bipod for testing purposes, but in the long term, I want something nicer. The best idea I've seen is from K8MRD - The which he's selling. I'll have to consider whether that's worth $45, since I figure I can make something for a lot less. I need to price aluminum arrow shafts on Amazon, or Craigslist, and mess around on TinkerCad with something to 3D print, or come up with something from the plumbing aisle, though I'm not hopeful for PVC that's a small enough diameter. Mike's pieces are printed in PLA, rather than PETG, which I think is not best for outdoor use.

Another obvious thing is that using the frame that holds the toroid and BNC connector is clearly not going to accommodate all the wire. Again, 3D printing comes to mind, or bodging something up using who knows what I can scare up. I've been meaning to try making my own "Micarta" using fabric and epoxy, so maybe this'll be the thing that motivates me to get that project restarted. I know there are cheap winders on Amazon and eBay, so maybe that'll be the ticket.

I finally got this antenna in the air today, at the Parker Radio Portable "Rodeo". Took longer than I expected to set up, and I'm pondering what improvements I can make in that regard, but in the end, I think there's not a lot of room. With ~66 ft. of wire, and only 28 ft. of elevation using a telescoping mast, it takes about 60 ft. of linear space - actually a bit more, since the mast bends a bit, and then there's guying at the feed end, the way I have it supported, plus the counterpoise.

Performance - I didn't end up trying to make any contacts, since the whole process of trimming it took longer than I expected. On the VNA, I got it below 1.4:1 across the 40M band, and usable on 20M. 15M and 10M were so-so. I didn't save plot images, since running the NanoVNA on my phone was, for some reason, a little wonky today. And with the sunshine, seeing the screen was a pain as well. I guess my ideal setup would involve a pop-up shelter or some other way to be in the shade.

I'll probably trim it a little more, to trade-off 40M against being a little better on 20M. It's likely I'll need a tuner for 15 and 10, and getting a Z-match kit is on my list anyway, though it's a low priority.

I don't know when I'll get out next, but I have a list of things to work on, and a better idea of what to expect. I can see why a lot of people prefer to use a coil-loaded vertical.

Sounds like you've got that antenna pretty well dialed in. That is a lot of linear space. Reminds me of a SOTA activation I did a couple of years ago up on Mt Evans, which is naturally a busy place, trying to deploy my end-fed random wire antenna. It was really difficult. My favorite antenna for limited space deployments is of course my Alexloop, but it requires considerably more weight and backpack space. The antenna itself is pretty light--finding a decent tripod under 5 pounds and <$200 is the challenge.

I really love my off center-fed dipole, which has an incredibly tiny Balun. The long end is 44 feet and the short end is 22 feet. When I deploy it, I attach the Balun to the top of my (6 meter) push-up pole, which shortens the actual run length of the long end to about 25 feet or so, and the short end has hardly any space requirements (maybe 10 feet). With a tuner, this antenna will work 40, 30, 20, 17, 15, 12, 10 and 6 meters. Total weight for the antenna is 7 ounces. I purchased my from Tim Ortiz (N9SAB) via eBay, but they?are easy to DIY as well; lots of plans out there on the interweb. Coupled with my Carbon6 pole, total weight is just over a pound. Add another pound for my tuner and 2.2 pounds for the IC-705--still a very manageable ~5 pound kit.?

And, for ultra portable work, I also have a 20M end-fed half-wave antenna, which I have coupled with an impossibly tiny 0.3 ounce Unun kit from K6ARK ($20). That antenna probably weighs 4 ounces and coupled with the Carbon6, still well under a pound. And no tuner required.?

I think that antenna design and building is one of the most rewarding parts of our hobby. Nothing like making your own antenna and making QSOs with it!

73,

Mark

---------------------
Mark Ehr | K0EHR

VP, 285 Tech Connect Radio Club
Littleton, Colorado

k0ehr@...
Check out my ham radio blog:

On Tue, Sep 26, 2023 at 09:53 AM, Mark Ehr | K0EHR wrote:

"I think that antenna design and building is one of the most rewarding parts of our hobby. Nothing like making your own antenna and making QSOs with it!"

My mantra for years regarding HF ham communications-,

?If you have a radio with 100w ouput and you cannot get satisifed? - you need a better antenna.

bud
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bud N0IA

• Plastic tent stakes are not the best - two of them broke
• I want to put some flags on the stakes, too aid in making sure I've picked them all up
• The "figure 9" cord devices work OK, but the ones I have are too big for "Handi Hundred" cord
• I will paint the figure 9 devices, again, to aid in seeing them for pickup
• I need a better guying solution - nothing serious here, just 1 more stake and easier deployment
• I'm going to consider replacing the heavy tripod - possibly a painter pole. 3D printing models for the threaded end are on Thingiverse, so making a combo guy point and tie-off for the feed-end of the antenna should be simple.