EMRFD Message Archive 7011
Message Date From Subject 7011 2011-12-13 08:11:29 Tim 160 Meter tuner success Maybe not the most solid-state subject in the world, but I did make progress on my 160M stuff and in fact came up with what I regard as a good 160 Meter antenna tuner.
You might remember that I have large BCB field strengths at my QTH, up to 50 V peak-to-peak in the AM broadcast band from the antenna leads.
My antenna for the ARRL 160 Meter contest, was a 130 foot doublet up 80 feet that I normally use as a dipole for 3.5MHz and up. But for 160 Meters, I tied the feedline together and fed the whole antenna against ground as a "double inverted L" or maybe a "T" configuration.
To couple to it, I made a resonant tank using an air variable (circa 800 pF) and a air wound inductor.
Bottom end of the inductor goes to ground. Top end of the inductor goes to the variable C.
I then tapped the antenna about 1/3 of the way from the bottom, and my 50 ohm rig about 1/4 way from the bottom. At this combination, I could get under a 1.5:1 SWR over maybe a 30 kHz bandwidth. I had to go very slightly tweak the air variable as I moved up and down the band in the contest.
All of this was at the base of the antenna.
I think this makes a fairly high Q tank be the antenna tuner. Often high Q is a disadvantage in a tuner because it implies high tank losses. But... the high Q right at the antenna feed point, really helped me clear up the remaining BCB interference on receive. And I got 450+ QSO's in the 160 meter contest too :-).