Be careful of the "doorknob" capacitors. When you get bigger than about 100
pf the temp coef will be such as to cause drift off design freq./ matching.
when using high power. Using a larger number of smaller capacitance or other
zero coef would be desirable.
----- Original Message -----
Sent: Tuesday, August 07, 2012 11:52 AM
Subject: Re: [TowerTalk] Looking for thoughts
> If there are only certain band segments that you wish to use, it should
> not be that difficult to make a box with fixed door knob capacitors and
> inductors that can be switched in with relays controlled by a simple
> switch box in the shack. The hard part might be figuring out what values
> to use.
> John KK9A
> To: firstname.lastname@example.org
> Subject:[TowerTalk] Looking for thoughts
> From: K8RI <K8RI-on-TowerTalk@tm.net>
> Date: Mon, 06 Aug 2012 16:49:17 -0400
> I'm thinking of mounting a tuner up on the tower to feed the 160 half
> sloper (single wire) as well as the 75 meter fan dipole and 40 meter
> sloping dipole with ladder line, so I'll need to add a few relays to
> switch antennas.
> This can be a simple manual tuner, remotely driven with air variables
> and a switched inductor, or vacuum variable and a rotary inductor, or
> even one of the MFJ 998RT auto tuners. If I build it, I'd much prefer a
> tuner that handles single and parallel wire without using a balun
> Unfortunately the 998RT only has a single wire and coax output. I can
> work around that and *apparently*, or at least some think it'd handle
> all the way up to 2500 PEP.
> Of course there is the problem with lightning and remote tuners mounted
> at or near the top of the tower. Grounding relays could be added.
> Roger (K8RI)
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