EFRW: some notes

[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]

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)]

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]

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.

[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]

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)]

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

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

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"