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Re: Topband: Detuning Relay Flyback Diode

To: "Brad Denison" <>, <>
Subject: Re: Topband: Detuning Relay Flyback Diode
From: David Cutter via Topband <>
Reply-to: David Cutter <>
Date: Sat, 23 Dec 2017 18:36:40 -0000
List-post: <>
The back emf diode slows the relay a lot and you can improve that with a resistor in series, fudge as required.
Here's another method:
in the drive transistor circuit, fit a small capacitor between collector and base. As the back emf builds up, a current will be fed back to the base which will tend to keep the transistor on. This results in a slower rise time and this can be controlled with the value of capacitor used. A resistor in series with the capacitor provides even more control. Fudge as required.


----- Original Message ----- From: "Brad Denison" <>
To: <>
Sent: Saturday, December 23, 2017 3:51 PM
Subject: Topband: Detuning Relay Flyback Diode

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.


Brad W1NT <>
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