This low pass (??) circuit lets me get on 160M CW and 75M SSB with very low SWR and no tweaking. I would need to tune when going down to the CW portion of 80M. The Variable Capacitor is a Palstar C600 and the Roller Inductor is a Palstar RI-28. I tried quite a few different L circuits (all of the 8 documented in the ON4UN book that has either two caps and an inductor one cap and one inductor and two caps, but this configuration seemed to work the best.
Right now I am just feeding in the lower left hand corner an its an Inverted U. As you can see – the total length of the “vertical” is actually 148′ – so its longer than a quarter wave on 160M, but not by much. This means its also about 1/2 wave on 80M, and I was surprised that 160M had a very low SWR – 1.06:1 and on 80M – with no tweaking of the components it is 1.5:1, and both are well within the Exper SPE 1.3 K amplifier, which was my design goal.
It would be nice to tune 40 and 30 as well – but just getting 160 and 80M was the absolute must. 40 and 30 are just “nice to haves”.
I don’t really know what is exactly going on – but am happy with the results. Because my 96 buried radials are mostly way too short – with only about 20 that are 50′ long, maybe the inductor tunes them since they are all kinds of crazy sizes and while they do fan out in most directions, its a crazy pattern. Maybe the capacitor on the vertical element takes care that it is a bit longer than a 1/4 wl on 160M and bit longer than a half wl on 80M.
If a reader can explain this – I’d appreciate it. I did not find anything regarding this in the ON4UN Low Band DX-ing book.
Unless someone warns me that what I am doing is not such a good idea, I will go with the u.RAT – because it is needed to cover the CW and SSB portions of the bands. I will try the grounded loop with this tuner – the Palstar BT1500A did not like it at all.
Because I have a great 40M array – I don’t have to worry much about matching this Inverted U to 40 or 30 – I found out that the 40M array works great on 30M and the SWR is already low. But still – it would be really nice if I could.