[Antennas] Need Advice / help

[Tom Bates]

I'm trying to help a friend on the west coast ( I'm on the east coast ) solve a
tuning problem with his W9INN antenna.  The problem only exists on 40M, and this
antenna is the 80 thru 10 M, 67 ft version.    He's using an IC746 with the built in
tuner.

By using an MFJ259B, he is able to get low SWR on all bands, and is satisfied.  The
problem comes up when he tries to transmit on 40M....  The auto-tuner comes on,
things whir and click, and the SWR shows high with the result being reduced output
power from the rig.

I have suggested a couple of things.  #1, a coax choke ( 15t RG-58, 6" dia ), and #2,
adding an indiscriminate length of coax ( suggested abt 30 ft ) between the rig and
existing coax feed as it is now.  The choke was tried, but did not help.  The length
of coax will be tried next.

It's my suspicion that the SWR detection circuitry is being confused by some voltage
or current anomaly that may be present on the coax just at the point where he
happened to cut it to connect to the rig.  But, I don't know how to measure this.

Any suggestions or theories?

Thanks for your help.  73,  Tom  AA1NZ