Dumb antenna question

[Electronic M]

Pipe is fine...Maybe overkill (I use lamp cord for my dipoles), but there's no kill like overkill. Generally the thicker diameter the wire a dipole is made of the better bandwidth it can handle.

Is your modulators output 75 ohm or 50 ohm? If you're feeding a 50 ohm amp with a 75 ohm modulator you could be getting impedance mismatch reflections and confusing them for harmonics.

Any piece of wire is capable of being an antenna at any frequency, how good of an antenna it is depends on size shape, intended use and a LOT of fancy math . (When I was a teenager we had one of the last cellphones with an antenna and at the family cabin where I had setup a 100' long wire for shortwave the folks were able to clip the cell antenna to the longwire and get cell service there for the first time ever.)