With silver-cadmium relay contacts I use on my ladder line switching, I
find I have to occasionally transmit a dit to get receive to work again,
especially if I haven't been on the radio in hours or days. My mental
model
is that I have to "blow through" the surface contamination. Would
definitely never use the silver-cadmium contacts in a receive-only path.
(Even though I have been known to make some Q's while transmitting on my
receive antennas, it was purely by accident!)
That's exactly what you are doing, blowing through a very thin surface
contamination.
There are a few common forms of high resistance or open contacts. The very
things that allow hot switching go contrary to receiving. For best results
contact overlay has to be gold, it has to be cold switched (or switched with
low voltage and current to not burn off the plating), and the contact needs
to have a small surface area. Some relays are split into multiple small
areas to increase contact area pressure and parallel areas.
The worse thing is a large area, because pressure across the area decreases
for a given spring pressure.
A second issue, now more prevalent with everything being made offshore, are
contaminants inside relays. The plastics can leech contaminants, or air
sealed inside just might be dirty. This usually cures itself over time.
Low frequency performance, tests, and specs don't mean much. Skin effect
seriously aggravates heating in some wires and contact current carriers.
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