I have been wanting to experiment with a random length wire antenna for some time.
My primary reason for trying one is to see if I can get a better signal in and out, on multiple bands, versus the fan dipole that I have in the attic. Furthermore, I think I can sneak one outside without the neighbors or HOA complaining.
I have learned that not all lengths of wire work well (for the bands you want to work). Apparently the lengths that are a half wave on any frequency (or any multiple of a half wave length) don’t work well as they will give you very high SWR. I am not sure why…but I trust those who may be in the know.
Mike, AB3AP posted a page which is a great resource:
Here are his calculated lengths to avoid (shown as areas in colors…white gaps or areas are lengths to use).
Mike’s graph goes out 535 ft…but I’ve cropped it here.
For those of us wanting to get moving quickly on this will notice that Mike wrote that a standard recommendation (see QST, March 1936, p. 32, “An Unorthodox Antenna”) is an 84′ long end fed and a 17′ long counterpoise (6.5′ for 20m). I may give this length a try.