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Re: Isolation transformer and 9600 baud.

Hi Alan.

> So, if a transformer isolation is not a viable option, could one use
> capacitors on both sides of the data line to give protective isolation, and
> still handle the signal properly?

Maybe not.  If a high-voltage transient were to come along, it would pass right
through the capacitors for a long enough period of time to cause damage to your

> Consumer sound cards have rather unknown
> robustness.  Of course I have been operating a hardware TNC, tied to the
> computer through the serial port, for years with no smoke.

Same here.

Just keep everything tied to a common ground, including the PC.  It might
also help to power everything you wish to connect to your computer (everything
that uses a 3 prong power plug) from the same electrical circuit (or common
outlet strip).

You might afford a measure of protection to your soundcard by connecting to it
through something like a 10k ohm resistor.  Then place a back-to-back series
pair of zener diodes (maybe 4.7 volts each) directly across the input.  In
this manner, you'll prevent anything beyond about 5.4 volts from entering the
soundcard, regardless of polarity.

73, de John, KD2BD

Visit John on the Web at:

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