[TowerTalk] Driving Remote Relays--simply

[k6xx at juno.com]

Remote Ant. Switch Operators:

Here is perhaps a simpler (and certainly more efficient) solution for sticky relays.

Given that relays need a higher 'activate' current than 'hold' current, what we'd really like to do is boost the supply voltage temporarily--long enough for the relay to move from OFF to ON-- then drop back to a lower voltage holding level. Yes, it is CURRENT we need, but we drive current with voltage, of course.

Several years ago, Tony, K1KP, presented a circuit designed to speed-up the large, clanky relays in Ameritron amplifiers. This circuit provides a short burst of double the supply voltage, then drops back to normal supply voltage. This speed-up functionality should be ideal for remote antenna switches (especially with long cables) as well. Virtually zero additional wear-and-tear on the relay, yet it gets hit hard, long enough to make solid, clean contact.

It takes a transistor, resistors, 2 diodes, and capacitor. No heat sink, no higher-than-normal supply voltage. Can be mounted remotely or in the shack (inside the control head) with similar results. (I'd wager remote mounting would be slightly more successful with extremely long cabling, but then you'd have to worry about the capacitor temperature rating, etc. Try it inside the control box first...).

I posted this design on my web site: http://www.k6xx.com/radio/fastrely.html

73 de Bob, K6XX

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