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[AMPS] wanted SB 220 bandswitch

To: <amps@contesting.com>
Subject: [AMPS] wanted SB 220 bandswitch
From: W8JI@contesting.com (Tom Rauch)
Date: Tue, 26 Sep 2000 08:26:22 -0400

> Regarding this business of legitimate bandswitch failures, methinks the
> bandswitch has such a high SWR at even moderate VHF power levels (say 10 W
> - 21 dB down on carrier level), that the contacts heat up, loosen/corrode,
> and fail as the years go by. Nothing to do with explosive VHF power
> levels, etc. 
> 
> For what it's worth,
> Ian ZS6BTE

The failure mode you describe is caused by dirty contacts.

Once a contact behaves that way, the plating is pitted. It makes 
progressively poorer connections, until eventually it has a heat 
failure.

The current is pretty high at HF, as is the voltage. You have both 
circulating currents and high peaks voltage to deal with in the 
resonant tank.

The VHF makes for colorful conversation, but isn't very likely from a 
technical viewpoint.

 
73, Tom W8JI
w8ji@contesting.com

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