EFRW: some notes

Do you have general comments, notes or questions you'd like to share with others? This is the place.
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Andrew (grayhat)
Posts: 167
Joined: Sat Jun 11, 2022 2:59 pm

EFRW: some notes

Post by Andrew (grayhat) »

Nothing particular, just a pair of links discussing the "random" wire antennas

https://f5npv.wordpress.com/endfed-rand ... w-antenna/

https://k8ua.com/2019/10/my-lid-moment- ... ndom-wire/

the first one is pretty long, but I believe it's worth reading with some attention, since it carries some often overlooked concepts which, once grabbed, will allow to squeeze out the max from an EFRW
KL7MJ
Posts: 91
Joined: Mon May 15, 2023 9:06 pm

Re: EFRW: some notes

Post by KL7MJ »

Thanks for the links - something to read over the weekend.
I think part of the "problem" with EFRW antennas is the name. They're really End Fed Non-resonant Wire antennas - not just random lengths of wire.
The biggest downside of a non-resonant antenna is that you need more junk in the antenna chain (tuner, SWR meter of some kind, common mode choke) it was a nice change this week when I was tinkering with a base loaded vertical that connected directly to my rig!
Andrew (grayhat)
Posts: 167
Joined: Sat Jun 11, 2022 2:59 pm

Re: EFRW: some notes

Post by Andrew (grayhat) »

well... the EFRW is not "random" as you already wrote, it's more an "aperiodic" or "travelling wave" kind of antenna, at any rate, the first link I posted, carries some concepts and facts which need to be digested to get a good grip on EFRW, so, if you want, take your time to read the whole "blurb", I think it will be worth; more often than not, when it comes to EFRW, people tends to set them up "as it goes" but that's a mistake imVHo since while the "random" is a simple antenna, it still needs some care to work at its best (see the 2nd link)

One thing I tried and is worth a test, imHo, is using a short run of wire connected to a ground stake in place of the counterpoise, it has pros and cons, but is something worth testing
N8TGQ
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Joined: Tue Jun 21, 2022 5:06 am

Re: EFRW: some notes

Post by N8TGQ »

An easy, simple rule of thumb that I learned helping my dad back in the 60s:

At least a quarter-wave on the lowest band you plan to work.
Not a half-wave on any band you plan to work.
Rick N8TGQ
Andrew (grayhat)
Posts: 167
Joined: Sat Jun 11, 2022 2:59 pm

Re: EFRW: some notes

Post by Andrew (grayhat) »

As for the EFRW radiator (wire) length, the "calculator" found here

https://k7mem.com/Ant_End_Fed.html#Not_Random_Multi

helps selecting a proper length depending from the desired bands
KL7MJ
Posts: 91
Joined: Mon May 15, 2023 9:06 pm

Re: EFRW: some notes

Post by KL7MJ »

I also have a script I wrote myself, that I can select which bands I care about - e.g. if I'm building an EFRW for a 10-20m rig, I don't care about interactions on 30m.

Having said that, I think we make EFRWs seem too complicated with the table of good and bad lengths.
For portable use, I think a combination of 29/17 is good enough for 10-20m, and 35.5/17 is good enough for 10-40m.
Can I load up shorter wires, sure, but I think that efficiency rapidly drops off for the lower bands.
Andrew (grayhat)
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Joined: Sat Jun 11, 2022 2:59 pm

Re: EFRW: some notes

Post by Andrew (grayhat) »

well, yes and no; a reference table or "calculator" will help avoiding some lengths which won''t "load" on some bands, so it's useful, then one may want to use an EFRW at home, so a reference may and probably will be useful :D

As for lower bands (say 80m) then it's mostly about choosen length, installation and counterpoise in own experience, by the way assuming the 9:1 and choke are up to their task and not wound using the first toroid at hand :D

basically the old rule of thumb applies "the radiator should be longer than 1/4 wave at lower frequency and not an even multiple of 1/2 wave on any frequency of interest, the counterpoise(s) should offer a very low impedance return path for currents at any frequency of interest"
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