parnass@ihuxf.UUCP (07/15/83)
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WARNING: This article may not be of interest to electronic
geniuses.
Have you ever used a tape recorder connected to your
receiver to monitor those hidden frequencies? Hidden fre-
quencies, to me, are those frequencies which may be used in
an interesting way but are difficult to monitor because of
infrequent usage.
Some of the higher quality scanners are equipped with tape
recording interfaces. A few days ago, I connected a Pana-
sonic cheapie cassette recorder, obtained by opening a sav-
ings account, to my Regency K500 synthesized scanner. The
interface consisted of two parts:
1. audio - I installed a 1/8" jack on the rear of the
scanner. I connected this jack, through a .01 ufd
disk capacitor to the high side of the volume control
potentiometer. This provides a medium impedance audio
output signal of constant level. That is, the level is
independent of the volume control setting.
2. control - I installed a small relay in the scanner.
The 12 VDC 1250 ohm relay coil is actuated by the car-
rier operated squelch signal.1 The contacts of this
relay are brought out to a 3/16" jack on the rear of
the scanner. These contacts control the power to the
tape recorder.2
With this configuration, the recorder records only when a
signal is being received on the scanner. Of course, if you
had a fancier recorder, with voice actuated circuitry (VOX),
you could just place the recorder's microphone near the
scanner's speaker. With my particular configuration, I set
the volume control on the scanner as low as it will go,
pressed the record switch on the recorder, then went to
sleep. When I awoke, I played back the tape.3 This is how I
__________
1. A diode across the coil contacts protects the scanner's
solid state circuitry against nasty reverse voltages.
2. As equipped from the factory, my K500 contained a
control interface that could sink only 100 ma. I added
the relay because my recorder used more current. I
think the Bearcat 250's solid state control circuitry
can sink 350 ma. The Bearcat 350 contains a relay which
can handle 1 amp.
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found some government stations mentioned in the Kneitel
book.
It took a finite, but short, amount of time for the
recorder's motor to come up to speed, so the first syllable
of a transmission was missed occasionally. This produced a
slight slurring sound on the tape in between transmissions,
which helped separate one transmission from the next.
Scanners equipped with a "count" feature, such as the
Regency K500 and Bearcat 250, contain a counter, the input
of which is connected to the same signal that I used to
activate the relay. One can get the scanner to display a
count of the number of transmissions that took place on the
frequency of interest since the last clearing of the
counter. This counter provided me with more information.
Needless to say, if it was zero after a long monitoring
period, I didn't bother listening to the tape!
Try it and have some fun!
Robert S. Parnass, AJ9S ihnp4!ihuxf!parnass
____________________________________________________________
3. The control interface circuit must be disconnected, or
shorted (in my case) to play back the tape.