[Boatanchors] TCS Tx & Rx

[Mike Hanz]

A single diode, regardless of whether you are protecting the key 
contacts directly or hanging it on the offending coil, does in fact 
affect the dropout time of the relay significantly.  Back when I was a 
young engineer, I designed relay testing equipment for high reliability 
weapons, and that fact was drilled into me big time.  There is a good 
rundown on the various methods of suppressing the spike from the 
collapsing magnetic field at 
http://www.pickercomponents.com/Pages/Application%20Notes/Coil_Supression_vs_Relay_Life.pdf 


Included on the second page is a chart of dropout time increase versus 
suppression technique that is more than illuminating.  A diode in series 
with a zener of approximately double that of the coil operating voltage 
is what we used in our circuit designs - the reason should be clear.  
Obviously you have to choose the zener rating carefully to manage the 
strength of the collapsing magnetic field, which varies with the size of 
the relay.

73,
Mike

> >  I'm no CW op but I'd expect the diode would lengthen the relay release
> >  time, maybe quite a lot.
>
>
> Some passive parts across the key might have a noticeable effect like
> that but the backward diode doesn't have any timing effect. If there is
> one it would take lab equipment (atomic clock?) to measure it. At morse
> code keying rates any stretching that might be there is 'virually'
> nonexistent. And..it *DOES* get rid of that spike induced when the
> magnetic field from the relay coil collapses. It's highly recommended in
> solid state circuits to preserve keying transistors that are used to
> energize relays.