[na-user] Activating External Voice Keyer

David A. Pruett David A. Pruett" <k8cc@ix.netcom.com
Mon, 16 Nov 1998 01:08:52 -0500

K4NR wrote:

I'm trying to find a way to interface my external voice keyer to NA and
DX4Win.  The usual 2N2222 circuit can be used to switch the 5 volts, but
how can you select which recording to use?  Any ideas on an interface?


I can't speak for DX4Win, but the NA protocol takes a LPT pin high for
around 100 mS.  The pins are as follows:

Message #1		pin 2
Message #2		pin 3
Message #3		pin 4
Message #4		pin 5

Ground is any pin from 18 to 25.

The next question to ask is what kind of signal your external voice keyer
requires?  Is it switch to ground or switch to some positive voltage?

Switch to ground is simple, take a 1K resistor from the LPT pin to the
base of a general purpose NPN (2N2222, 2N4401, etc.), emitter to ground,
collector to the voicekeyer.

Switch to positive is a little tricker.  This is the circuit I needed
for my MFJ voicekeyer that I use with my laptop.  Here I used an opto-
isolator (NEC PS-250x family) which is great because there is no direct
DC connection between the computer and the voicekeyer (and hence, the 
radio).  The LPT pin connects to the input side of the opto thru the
1K resistor to computer ground.  On the output side, the collector of
the opto output goes to +5V (conveniently provided on the connector
at the back of the MFJ) and the emitter goes to the message select
input.  Depending on the design of the select inputs, you might need
a series resistor here.

I've used this setup twice from the Caribbean and once for FD from
home with zero problems, either logically or RF hum-wise.

One problem you might watch for, one some voicekeyer the switch
inputs are scanned in a row-column setup.  This can be tricky to get
to work.

I hope these comments help lead the way.



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