Topband: TX relays

[Stan Stockton]

Tom,

What would be a better choice for a stack match?  

I'm quite sure that in the heat of a contest these things have been hot switched on rare occasion with 1500w.  There was one time when I intentionally hot switched one of them with 100w because I thought the receive signal was down 10dB or so.  Problem went away.  Anyway I've been using them for about 6 years or so and only had one that failed after a big lightening strike.

Stan, K5GO

Sent from my iPad

On Oct 10, 2014, at 7:29 AM, Tom W8JI <w8ji at w8ji.com> wrote:

>> I have built four or five "stack matches" using these relays and have been quite pleased with them.
>> 
>> http://www.mouser.com/ProductDetail/TE-Connectivity/T92S11D22-12/?qs=%2fha2pyFadujQKxyiQ9QJsU9gOmzykpctnwthD3xoZjoJPHbNrun4hw%3d%3d
>> 
>> 73...Stan, K5GO
> 
> If you look at the contact material, it is the wrong material type for our applications. Those relays are hot switch relays for high current applications with Silver Cadmium Oxide. From an engineering bulletin on selecting relay contact materials:
> 
> Silver Cadmium Oxide
> 
> Silver cadmium oxide contacts have long been used for switching loads
> 
> that produce a high energy arc. Silver cadmium oxide contacts are less
> 
> electrically conductive than fine silver contacts, but have superior
> 
> resistance to material transfer and material loss due to arcing. They do
> 
> exhibit greater interface resistance between mated contacts, and also a
> 
> slightly greater contact assembly heat rise. The minimum arc voltagerating
> 
> of silver cadmium oxide is 10 volts and, like fine silver contacts, the silver
> 
> in this alloy will oxidize and sulfidate. Therefore, an arc is necessary to
> 
> keep these contacts clean.
> 
> 
> This doesn't mean they won't work and will go up in smoke. It does mean they are subject to contact sulfidation which causes intermittent receive. They have silver, a hard base material, and large contact area that does not wipe well. They also are the type of relay that is subject to contact derating from skin effect because of constant resistivity.
> 
> 
> 73 Tom
>