Topband: Relays in RX array

[Ford Peterson]

> Can anyone point me toward a practical circuit for running a few ma at 12 volts through the relay contacts of an antenna switching system, so as to keep oxidation from building up?  The subject has been discussed from time to time here but I don't recall any references to an actual circuit.  I will have 12 volts available at the relays, but am unsure how to handle isolation of DC and RF circuitry.
> 
> Thanks in advance.
> 
> 73, Pete N4ZR

Pete,

I had a thread on here last year that discussed the topic at length.  The bottom line was that all relays will be flaky due to oxidation and other issue on the contactors.--unless you run a bit of DC through them.  How much DC?  It depends on the contact materials.  Most materials I found needed 10.5v and some as high as 100ma.  I experimentally found that even just a few ma was beneficial for the relays I was using.  I set mine to 10ma and have found that after leaving them unused for long periods, I will come back to find them open or attenuating the signal.  Flip the switch once and they work fine once again.

There are several manufacturers that have app notes on the subject.  Obviously, a complete dissertation would occupy volumes.  The KISS method dictates to run some DC through them.  If there are problems, run some more.

Ford-N0FP
ford at cmgate.com