K1XM writes:
> I'm building a keyer and headphone switch box for my small contest
> station. I have a few questions:
>
> Some keyers use optoisolators for the key and PTT lines and others
> just transistors or FETs such as the 2N7000. Has anyone had an
> experience where the optoisolator actually helped or saved equipment?
>
> Some headphone switches use transformers for galvanic isolation. Has
> this solved problems for anyone? And can anyone recommend a source
> for a good transformer for this purpose?
>
> I understand that isolation and transformers "good things". But if I
> put all good things in this box it might not fit in my small contest
> station.
I have seen some problem associated with ground loops go away when
properly using transformers for isolation. I think this is most
important on transmit audio than on the headphone side - but if you
are connecting up different radios to one set of headphones (and thus
sharing a ground) - you might have some RFI with the ground loop.
I am a big believer in dry contacts for PTT and CW. This eliminates
all sorts of possible issues (grid block keying, strange PTT voltages).
I like to have two sets of PTT contacts so that I can use one to drive
the amp directly (some radios have whimpy relays for that and some amps
have pretty high voltage on their relays). I have been sending CW with
a radio shack reed relay now for 10 some years - and it is holding up
just fine.
Tree N6TR
tree@kkn.net
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