Jos wrote:
>We encountered this problem in audio freq switching years ago, even with
> sealed relays. The cure, let flow a DC current of some mA
> similtaneously with the micro Amps of the functional AC signal.
>
> Jos on4kj
Jos, and others...
My quest for suitable relays continues. Many have suggested that I simply use
vacuum devices. This bullet-proof approach would be the natural 'fix' to the
problem of unreliable relay contacts. At $38 each, the solution would require
8 devices, costing around $300US. All of my projects include an 'engineering
review' by the XYL, who is particularly thrifty with respect to the family
'purse.' After she watched me bury $500US of wire in the back yard 2 weeks
ago, this issue requires some sensitivity on my part. I suspect others can
relate to my concerns.
Several have voiced similar opinions as Jos. A redesign of my project
concluded that I could fabricate my box using an idle current. Last night, I
configured a test fixture using one of my seemingly worthless relays (albeit
still $24 worth) purchased at the surplus emporium. The purpose was to run an
idling current through the relay while simultaneously checking the contacts
using an Autek VA1.
The fixture included a DPDT design, a balun bifilar wired as a monoband
isolation transformer rather than the wideband Guanella style, and approximatly
100ma of DC. The relays performed flawlessly the first time and every time,
even with the low level (+10dBm) signal being used. Removing the DC idle
current rendered the relay worthless once again. How little current can be
used and still get reliable connections? The DC load in my fixture is
approximately 1.2 watts, (i.e.12v @ 0.1A), which seems wasteful and likely
excessive. Can the same trick be performed using uA? How much idle current is
generally required to achieve reliable connections?
Thanks to all for the input. I (and my XYL) appreciate the help.
Ford-N0FP
ford@cmgate.com
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