[TowerTalk] Trimming 75 ohm hardline

[Steve Zettel]

A question for the combined wisdom of the reflector:

I was trimming some 75 ohm hardline, 1/2" Commscope variety, to get a half wave at 7.0 mHz so I could feed my stacked F12 C-3E tribanders at something resembling 50 ohms on the even harmonics. I am terminating one end with a 50 ohm non-inductive resistance, the other end I've terminated in a plumber's special to PL-259 fitting. I am measuring SWR with an Autek RF-1 Analyst; I am not measuring in any strong BCB or other RF fields that I am aware of.

I started off quite a bit longer than the length predicted by the formula:

	 1/2 X WL X VF
 
I've got a 1:1 SWR right now falling between 7.00 and 7.3 mHz, although centered somewhat higher than I'd like around 7.175 mHz; and 1:1 points falling in the 20, 15, and 10M bands, too. This is at 232 feet of hardline. Interestingly, there is a 1:1 SWR point below 7.175 mHz at around 6.1 mHz. Does this indicate that I should continue to trim until I've "raised" this lowest 1:1 SWR point to 7.025 mHz, or leave well enough alone? At 232' I'll have some excess to coil up and I can live with that; what I don't want to do is cut the hardline too short and have to splice some back in.

Thanks for the hand-holding,

Steve Zettel  KJ7CH
near Libby, MT USA 

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