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[Amps] Fast Relays

Subject: [Amps] Fast Relays
From: Peter Chadwick <>
Date: Wed, 11 Jul 2007 10:34:04 +0200 (CEST)
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It's probably teaching grandmother to suck eggs......
Reed relays can be very disappointing at RF, because of the skin effect. I 
believe you can get reeds with suitable plating to keep the RF resistance down, 
although I've not looked for some time. I found out the hard way about 40 years 
ago.....the RF resistance of a high voltage reed switch was such that about 2 
amps, the thing heated up past the Curie point of the reeds and opened. Then it 
cooled down and closed, cycling on and and off. There was also an HF receiver I 
worked on where there had been an attempt to use fairly cheap reeds to switch 
the tuned circuits: the reduction in Q killed the image rejection.
Putting a bit of DC through low level contacts works wonders. The FT102 is 
renowned for relay problems on its low level RF switching, and they are wotsits 
to change. In mine, I bleed a bit of DC through the contacts, and I'm still 
using the same relays that Yaesu fitted in 1983. But then, any of your old 
telephone men from the days of Strowger exchanges could tell you that......
Peter G3RZP
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