parnass@ihuxf.UUCP (07/15/83)
- 1 - 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. - 2 - 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.