The QRPer Board

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

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!

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

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.

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

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.

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"