I thought I had written about this once before but I looked into my archives and found nothing. I did do tests previously on 44 feet of wire for my EARCHI Matchbox and I thought I would revisit what the optimum length is for a random wire.
The random wire antenna is probably one of the least expensive, easiest and cheapest HF antennas to use if you have a tuner and you want to get the "most" out of a length of "random" wire without having to pull out that calculator, doing the math, getting the center insulator built or bought, running the feed-line, and all the rest that goes with putting up a more elaborate antenna.
However, there are lengths to avoid because if you pick that wrong length, the tuner may not work in one or more bands
Jack, VE3EED, solved the major headache of doing all the math of figuring out what the multiple of half wavelengths of the ham bands are. These are the lengths to avoid.
So in a nutshell - Here are the lengths to use which form a sweet spot for tuning all the ham bands. All the numbers are in feet. Make a note of it.
29 35.5 41 58 71 84 107 119
Well does it work? Before I settled on 41 ft, I used 50 feet which is also OK but I found that with 50 feet 80m is difficult to tune. 41 feet is much better. I did give up the tunability of 30m but the tuner in the KXPA100 does not have a problem. All the other bands are a cinch and 12m is almost resonant. All the SWR figures will change with length of feedline so don't worry about it and let the tuner do the work.
VE3EED is now SK but the internet article can be found here
The visual solution to the coding that was done Jack is here
Contacts made with the end fed random wire using the EARCHI matchbox are all with 50 watts and the KX3/KXPA100 are G0ORH, KR5N, MI0AHH, EA6NB, EA8/DL2DXA CO8LY on the WARC bands during the tests I conducted today. This will serve as my backup antenna for the DXpedition to Saint Pierre. It can be deployed as a dipole or an inverted L vertical.