Topband: Feeding the Shunt Fed Tower

[Dennis W0JX]

I have been using a shunt fed tower on 160 since 1979. My first was a 60 foot Universal with a TH6 on top. The shunt wire was three #14 wires twisted together and tied to a three foot aluminum tube very near the top of the tower. It was fed through a simple, single variable capacitor with a voltage rating of about 3000 volts.


The second version was a 70 foot Universal with the TH6 and later a stack of three beams. With a taller tower the shunt tap came down to about 56 feet using the twisted wires.

The third version is the current 80 foot Universal. The shunt feed was changed to 1/2 aluminum CATV hardline. This year I changed the bread slicer to a vacuum variable (approx 600 pf) and use an air variable as an Omega capacitor. My tap is now at the 48 foot level. My tower appears to have a natural resonance around 1765 khz.

After years of turning on the rig and send 20 watts out to the gamma, and then running outside to tune for minimum SWR, I had a brain spasm this year and took the MFJ SWR analyzer out to the capacitor box and hooked it directly to the coax connector. Then I tuned the vacuum variable and omega cap for minimum reactance and SWR, 1 to 1. Works like a champ!

73, Dennis W0JX/8
Milan, OH