The feed is a simple L-C circuit, left, and the antenna can be switched between being an Inverted U or Grounded Loop, right
Jan, OM2XW, wrote and reminded me of an antenna that is in the ON4UN Lowband Book, and one I have never tried. AA7OK has a VERY nice write up with great references at his web site – http://litlisten.com/aok/ As I understand it – Jack Belrose, VE2CV originally proposed this antenna some years ago. I will look at the ON4UN book again when I get home tonight.
Thanks to Jan, I am now seriously considering an antenna that will very easily replace the Mod Bob, and the only thing I need to do is take down the center wire support (a big plus), and move the feed and matching unit farther away from the house and my Array Solutions switch (another big plus). The first plus is that it become s a simpler configuration, and more importantly, the center elements and feed of the Mod Bob are too close to the house, and when I transmit at full steam, the Trane heater turns on! In the past, when I had the feed for my single vertical, I had no such interference.
I will do some modeling and also check it against the Inverted L, which is even simpler yet, but one thing for sure – I will be replacing the Palstar BT1500A with my “u.RAT” remote tuner at the base. I have a Comet vacuum variable capacitor, and might even try experimenting with that.
The KPOD and the Raspberry Pi are in the shack . . .
An additional wire would be used to switch the far end for the Inverted U / Grounded Loop. The best thing is – I have everything in place, and this will be a very nice weekend project. I can even get the control box and u.RAT ready – knowing that the actual components at the base of the vertical with the feed could be any combination of Land C and air variable vs. vacuum variable.