Hams in Space!

Number8 on your FHdbM:k e.rd
Touch-Tone
Activated Scanner
So you won't miss a call!
by Don Moser AA7Y
I
ne xpe nsive , wide-frequency
cove rage scanners have been
developed into val uable tools for
the amateur radio operator. There
are, however, two drawbacks thai
keep them from reaching their full
potential. First, when you're scanning
a number of busy repeaters
and simplex frequencies , and Bert
and Ernie tie up one repeater. your
scanner will most likely be stuck
there. If someone tries to call you
o n another frequency, you won't
hear the call . Secondly, you (and
the rest of your household) will
have to listen 10 Ben and Ern ie so
you won't miss a call eventually
directed to you.
A Loglcal Solution
A Touch-Tone decoder alone, connected to
a scanne r, will solve the second problem; you
won', nave to listen to all the traffic until
YOU'fc called. But it won't solve the first
problem of the scanner getting hung up on a
busy channel. Combi ning the logic of the
decoder and the scanner will , however, solve
bot h problems.
What happens when a no rmal sca nne r
switches to a busy frequency? The squelch
c ircuit detects a carrier and outpu ts a logic
control signal that tells the scanner to stop
scanning. To operate as a Touch-Tone activated
scanner, I've opened the logic control
line coming from the squelch c ircuit and insertcd
a logic signal from the first
decoded d igit of an Auto-Kall
AK4 Touch-Tone decoder. The
scanne r won' t stop unless it re ­
ceives the first digit ofyour code.
If the scanner is programmed to
scan 10 frequencies, and it's scanning
at the rate of to channels pe r
second , the calling station mu st
hold down the first digit ofthe code
for at least one second. Th is gives
the scanner enough time to make
one complete cycle through all the
frequencies. Once the first digit is
30 73 Ama teur Radio Today. March,1991
•••
Photo A. The author modified the Motron Auto Kall AK-4 to solve
two common problems.
decoded. a timer is set that stops the scanner
for about 10 seconds, allowing time for the
decoder to receive the rest of the code. If the
right code sequence is not received within 10
seconds, the scanne r resumes scanning . If the
correct code is received. another timer is
triggered that both turns o n your speaker and
keeps the scanner tuned to the calling frequency
. The calling stat ion identifies and
tells you which freque ncy he's calling on.
I've been using thi s system for several
years now, and it's been a real life-saver. We
have fou r speakers connected to the scannerl
decoder a nd placed at strategic pl aces
throughout the house and shop. My wife can
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