[CQ-Contest] Optical and galvanic isolation

[Tree]

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 at kkn.net