[TowerTalk] Detuning Booms ...

[Tony Brock-Fisher]

Well, I had really hoped to be able to share a success story about detuning booms, but unfortunately all I can report is a 'result'...

Situation:

KT-36XA at 80 feet, 8 feet above a 40-2CD on a swinging gate mount. Both antennas can rotate, independently. As I have reported here before, there is a significant interaction where the SWR on the 40 rises to 2:1 when the boom of the XA is parallel to the elements of the 40. (i.e. antennas aiming 90 degrees apart).

Experiment:

As part of a recent rebuild of the XA (let me know if you want details), I added wires from the boom joint bolts back to the boom/mast plate area. I tested this with a variable capacitor on the ground, and found that a 200pf variable would resonate nicely at 7.150. I built the capacitor into a weatherproof enclosure. The XA has subsequently been reinstalled, and today I went up the tower to install the capacitor. While at the top, I was able to use an Autek RF-1 to get a very nice series resonance with the capacitor and the boom of about 9 ohms minimum (a la W8JI references). I removed the RF-1 and connected the capacitor in parallel with the boom wires.

Result:

No discernable difference in SWR behavior. I had hoped this would break up the resonance enough to allow the 40 to think the XA was not there. Obviously I missed something.

73,

Tony, K1KP