I'm surprised that so many are still using the circuit that
Paul describes. For about two bucks at the local electronic
supply house, you can get an opto-isolator with a Darlington
Pair output. The input to the led is thru a 1000 ohm resistor,
the other side to ground.
Then, here is the neat part - Don't ground the emitter of the
output, but run the collector and the emitter to the key line
of the transceiver., and if it is backward, reverse the leads.
Handles both negative and positive keying with no changes.
AND - Zero digital hash can pass from the computer to the rig,
there is no path for it.
Cost and size about the same as using the transistor.
From: John & Annette Nicholson <firstname.lastname@example.org>
To: Paul Meier <wa7mig@Hevanet.com>
Cc: email@example.com <firstname.lastname@example.org>
Date: Thursday, November 05, 1998 7:13 PM
Subject: Re: [TenTec] 301 Advice
>The circuit is a simple one! Just one transistor, a 2N4400 or
>equivalent. Basically, you make up a cable with a male db25
>connector on one end and a 2 conductor key plug on the other end.
>Transistor connections to the male db25 connector end:
>The emitter goes to pin 1.
>The base goes to a 1K resistor (in series) and then on to pin 17.
>Pin 18 goes to the ground side of the cable going to the key plug.
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