It appears that almost anything which a bi-polar transistor can do, an FET can do better The simple regenerative 3.5 to 6.0 mhz receiver described here is another case in point.
Three or four months ago 1 started out to build an SWL receiver for my ten year old son. i used the circuit shown in Fig. 1 which is similar to that in the December, 1966, issue of 73 Magazine. There were two problems with it which I could not seem to overcome. The regeneration control was too critical, or at least I could not get it to remain stable over more than three or four hundred kiiz. It required an excessively long antenna. When I got around to measuring the power into the regenerative detector, it turned out to be .8 ma at 7.5 volts or .0006 watts. I guess you can t expect to rattle the diaphrams in your earphones with that sort of power. Maybe what is needed is a detector in which the regeneration is not controlled by reducing the collector voltage.
This thought led me to recall the old two tube blooper that started me on my radio career circa 1932, It had a VT224 as a detector and regeneration was controlled with a variable capacitor From that point the circuit shown in Fig. 2 evolved, I used a TIS-34 FET because: (1)1 had some on the shelf; (2) a :ET acts like a screen grid tube (with poor screening). Any FET which will oscillate on the desired frequency will work in the same circuit (keep the N-Chaftnels and the P-Channels straight).
The results of this new design were as surprisingly good as the old circuit was disappointing. The regenerative control is so stable that you can actually tune the whole range, 3.5 to 6.0 mhz, without touching the control The oscillator is sufficiently stable so that it could be used for a VFO. It will not only receive SSB signals, but in fact it will sit on the same signal for a half hour or more without any need to retune. 1 can pick up plenty of signals with a whip antenna (and in some cases no antenna at all). CW signals have a clear crisp sound to them that makes them pleasing to copy.
Before we get carried away completely, i had better acknowledge that this ^blooper" suffers from some of the same ills that caused the decline of the 1932 tube-type "blooper/' Selectivity is almost nil- Any other amateur within three or four blocks of your location will put one whole amateur
Fig, Circuit diagram for "The Novice Pair/1 W6JLL, December, 1966, 73,
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