Ham Radio - The Doublet. An old but good multi-band single dipole antenna. Part 1

I'm running an ~ 105 foot (could be a little longer) doublet with about 115 feet of 400 ohm line.

It works FB 160-20 with a home brew T net tuner and 1:1 balun (2 x FT240-43 wound with #12 pair stripped from some romex).
I have a Johnson matchbox. The T net works just as well on 80-20 and as a bonus covers 160.
I also used a Vectronics VC-300DLP for a couple of weeks but it's too small to use with an amp.
The VC-300DLP is a T net with a built in 1:1 balun and also gave a good match on 160-20.

While it loads on 160, the doublet does not get out well on 160. It slopes between ~50 to ~70 feet above ground.

 

I use a 40 meter dipole at 50' fed with a half wave of 450 ohm window line to a 1.5:1 balun. The SWR is less than 1.1:1. Using 1 KW during contests I cause pile ups in Europe. The theory is that a half wave transmission line mirrors the impedance on one side to the other. The dipole is supported on either end, so it was not possible to suspend a balun in the center. Light weight window line solved the problem. The 67' of window line is routed in a big U to prevent mutual inductance. I modeled this on EZNEC and the performance is close to the model.
AF4RK