I installed the URAT out back at the base of the “Mod Bob” antenna. I experimented for a few hours and I was able to get a decent SWR on 160, 80, 40 and 30 by doing this:
There is one wire left in the control cable, this means with a clever use of a relay or two, you could bypass the capacitors for 160 and 30M. Here is a relay board that could be controlled with that last signal wire coming from the Raspberry Pi GPIO:
I’m pretty sure a simple DPDT relay does the trick – its NO or NC which means it will normally be set for 80 and 40M or 160 and 30M – and by using a button on the KPOD – or a simple switch in the control box – you could send that signal to the URAT relay and bingo!
This means for about 1/2 the price of the Palstar BT1500A, you can have an remote controlled balanced feed tuner. If you have the junk box parts – it would be less of course.
HOWEVER, I’m very spoiled by the Palstar BT1500A. It was $720 and worth every penny, by far. It’s design and high powered components give me the confidence that my antenna is coupled to my solid state amplifier, which is less forgiving SWR wise than the tube amplifiers, and every detail as far as matching the Mod Bob fits like a glove.
This has been the most interesting ham radio project I have ever worked on. I have learned so much – its really quite amazing. The project was rich in facets – antenna, matching circuits, Raspberry Pi, stepper motor control, a fun use of the Elecraft KPOD, and much more.
Its way too hot to go out and replace the URAT and put the BT1500A back out – so I will do it first thing in the morning.