[ARC5] Keying suggestions

[J. Forster]

David Stinson wrote:

> ----- Original Message -----
> From: "Ian Wilson" <ianmwilson at earthlink.net>
> Subject: [ARC5] Keying suggestions
>
> > I'd like to key an unmodified ARC-5 TX using the internal relay.
> >
> >     a) I know that originally, the relay in the modulator did this
> >     b) will apply the reversible mod that leaves the antenna relay in 'on'
> >        position
> >
> > What R/C snubber components should I use around the key? Should I use a
> > spike-catching diode?
>
> I would recommend the spike diode, but I've never used
> an R/C snubber.  If you're just keying one relay, I don't think
> it should be a problem.
> 73 Dave S.

I've not looked at the keying circuit specifically, but this is true of the two
types of snubbers in general: With a diode, the relay will drop out more slowly
than with an RC snubber. The reason is that with a diode, the coil current falls
with a time constant of

L/R, where L is the coil inductance and R is the coil resistance

With an RC snubber it falls with a TC of

L/ (R + Rs) where Rs is the snubber resistance.

Basically, some of the coil's stored energy is dissipated in the snubbing
resistor. So keying may well be better with the RC than with the diode.

-John