Topband: TX relays

[Tom W8JI]

> 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