Tech Notes from the Field

The scenario: New 445′ tower, two AM stations diplexed, shunt fed.

Who thought of 445′ for stations on 1040 and 1240? Not a good beginning.
Three legs, each a climbing leg, one with a safety-climb cable.
Center feed to two sets of 3 skirt wires. That makes 6 skirt wires. Kintronics designs the skirts to go up each leg, that makes for 2 skirt wires per leg, and separated by approximately 36″. To me that is a bit too close for comfort. Lots of interaction.

Two storms now and each time the safety-climb cable comes loose from their clips. One time entangles 1240, the next it attacks 1040.

Repairs are made today and new clips are added to supplement the existing clips. The cable is run and looks good. Turn on 1240. It comes up OK. Turn on 1040 and it does not like what it sees. VSWR foldback and settles on low power. Engineer comes out and tries to tweak it. No go. I check the ATU’s and connections. All look good.

Conclusion: The cable was never installed properly and the impedance measurements and sweeps were not correct. 1040 needs to be tuned to make it work. Break out the bridge!

It is amazing what a “little” change will do to such a system. Shunt fed is fragile enough, but to put it on a tower at such an odd height is nuts. Then instead of having the skirts go up the face with some good physical separation, they are run up the legs. Now you cannot climb the tower without shutting it down. It will be interesting to see how far out of tune 1040 ended up. 1240 is slightly out as it was not happy after the connection checks on 1040. A mess it is.