Multiband Antenna Switching

When I first started on this project I think my goal was to “magically” handle SWR on several bands and my area of focus was on using an UNUN or Current Choke to do so. They did do what they were supposed to – to a point, but there was no “magic” there. They did bring the match “close” to the range of the SPE Expert 1.3 amps internal ATU, but not quite close enough.

Knowing that the antenna was a little short on 160M, I added 10′ of wire which brought the resonance on 160M down into the CW portion of the band nd this is with the 1:1 current choke “Position 3” switched in:

The SPE ATU now handles 160M without the need for the AT2K!

and with the 1:2 UNUN in position 2:

30M also no longer needs the AT2K tuner, the internal SPE ATU is fine.

80M in Position 2 is improved, but not good enough. HOWEVER, because Position 1 is a total bust, I will replace Position 1’s 4:1 UNUN with a vacuum variable cap or other tuned circuit to give me a good match on 80M.

In retrospect, I could have probably just hung three loading wires off the top of the 41′ vertical and trimmed them for 160, 80 and 30M and achieved something similar – at least on 160 and 30, but I suspect 80 and 75M being a spread of 500 khz requires some kind of switched or variable tuned circuit.

I’m going to guess that 80 and 75M will need some variable capacitance. I might first try to just add a variable capacitor replacing the 4:1 UNUN, then try a tuned tank circuit. What’s really nice is – there is enough room out in the box, and I have plenty of control wires left if I care to remotely tune this tank circuit as I did with the URAT.

Lets look at what adding 10′ of wire did overall:

Position 1 – add 10

Position 2 – add 10

Position 3 – add 10

I think using Position 1 for 80M will be a winner, and I will be able to obviate the need for the Palstar AT2K tuner.

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