I DÎSCRIM J OUTPUT
Fig. 3. Junk box converter using two diodes and one transistor.
switch incorporated into the unit might be an unnecessary luxury, since the Mfe of the battery almost corresponds to its shelf life.
Any silicon diodes might be used, preferably those having similar characteristics. Any transistor may be used, NPN or PNP, with due care being taken to observe the polarity of the battery and the proper connections of the coupling electrolytic capacitor
(Figs- 3 and 4). While this unit used one of the commonly available 88 mH surplus to-roids, a horizontal width coil of the variable type, 45-215 mH (130 ohms), such as Stan-cor WC 14 or J, W. Miller type 6330 or 6324, might also be used, (All of the above parts were found in an old TV set, except for the silicon diodes, transistor, and 9 volt battery.)
The base (of 3/64 inch holed perforated metal) used was the cover for the horizontal deflection compartment of the TV set. 6-32 self-tapping screws lock in these holes nicely, (also from the TV set)* The transformer used from the TV set was the speaker output wired backward 4 to 5000 ohms (estimated) and could be replaced by any transformer in the junk box having a good step-up ratio; even a 6,3 to 115 V filament transformer will work well.
In the author's particular case, being a RTTY enthusiast, and having full RTTY facilities, including a RTTY tuning indicator, the toroid of 88 mH frequency was uned to 2975 Hz. When incorporated into the M derived low-pass filter used as a discriminator (Fig. 5), its frequency became slightly less than 2900 Hz. (If you wish to duplicate the
CV 172, then more capacity is required across the trap inductance to tune to 2300 Hz.)
Connect the converter to the audio output of a receiver. Tune in a commercial RTTY station. As you tune through the RTTY signal (with bfo onv, you will reach the point as seen on a scope (placed at the
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