Paul,
> 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?
>
I use optoisolators (4n25) for keying PTT and KEY lines, but never
experienced a dangerous situation about this stuff. I just noticed that
some computers use to send a logic "1" to the RS-232 at boot, with a
variable voltage. Since you have a fixed logic "1" voltage on the the
optoisolator output (fixed by you on the transistor collector), you are
surely safer in case of higher output voltages due to computer
misfunctionings. Obviously, this could also be done with a simple NPN
transistor.
4n25 is just easier and faster to change in case of buring during a
contest :)
> 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?
>
If you refere to the computer-radio connection, it did. I remember a 5
years ago CQWW, 1 hour to contest starting. I was trying to get audio
recording working with an old laptop, just connecting an audio cable
straight to the SB input (as I had been doing lot of times for fast
packet access). After some minutes of bad words, I noticed that the
cable was pretty hot, since a large amount of current was flowing
between audio output and the SB input, due to potential differences
between the two subsystems.
Fortunately, the radio was safe, but I have never been able to use the
laptop SB anymore.
If you are talking about this, I bought and used succesfully RS 273-1380
and RS 273-1374
Otherwise just forget it, but I'm curious to know what you are talking
about!
Alessio, IZ4EFN
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