Topband: Detuning Relay Flyback Diode

Tim Shoppa tshoppa at
Sat Dec 23 11:05:31 EST 2017

Whether a flyback diode is needed depends on what is driving the relay and
whether it needs snubbing.

Adding a flyback diode substantially lengthens the time it takes a relay to
open, which may or may not be an issue. What was a 6ms relay will become
several times longer on open. There are better snubbing networks to use if
you are time sensitive.

If the radio is keying both the detuning relay and an amp, you want to use
some series diodes to prevent sneak paths between amp key voltage and your
detuning relay voltage. These isolation diodes do not add any delays.

Tim N3QE

On Sat, Dec 23, 2017 at 10:51 AM, Brad Denison <brad.denison at>

> I have a couple of 6ms 12V Kilovac relays wired up as a detuning circuit
> during RX.  One question comes up before implementation regarding flyback
> diodes - would they be needed?  Seeking opinions on this question.  The
> relays are powered during TX and not powered for RX direct keyed by the
> radio with no sequencer.
> Thanks,
> Brad W1NT <>
> _________________
> Topband Reflector Archives -

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