[TowerTalk] Tuning vertical SWR-Analyzer vs SWR bridge

[Phillip Zminda]

I installed a 6-BTV vertical about a year ago. It is ground-mounted with about 60 radials and fed with Bury-Flex coax. I felt that the SWR was where I needed it. Over the winterI saw a shift in the SWR to the high end of most bands. I suspected that some clamp loosened and a dimension changed. I started to re-check dimensions and checked all my coax connections and did not see any problems. I began to suspect a trap leaked or got out of adjustment. As I began to try re-tuning I found that when I checked SWR with my AIM-4170 analyzer or an MFJ-259B the SWR showed a the dip at a much higher frequency than I see with the SWR meter in my radio (tuner bypassed), a K-3, or on an external SWR bridge. I have to assume the radio should be the preferred tool since the rig will fold-back if it doesn’t like the SWR. I have tried calibrating the AIM with standards at the end of the coax and have also used a new run of coax.

My real concern is the lack of consistency between the analyzers, which are close in readings and the SWR meter at the radio. I have been using my Argonaut VI and a separate coax to tune but still having difficulty seeing the low point on several bands. I am looking for ideas of what can cause such a discrepancy between the analyzers and RF from the radios (typically 5 watts). Any suggestions appreciated.

Thanks,

Phil N3ZP