Many thanks to everyone that replied to my connection question.
This driver circuit is quite strange, convoluted at best.
Food for thought...
Apparently, Q4 is used to gate on and off the oscillations generated at Q6 (and open the collector of Q6). The divider formed by R17 and R18, in concert with D1, apparently bias Q6 such that an oscillation is produced by feedback from the "antenna" when Q5 is on and Q4 is off.
Other than the very brief period (determined by propagation delay) following Q4 turn-off, when Q4 and Q5 are both turned off for 150ns or so (and the base of Q6 is held low by R18) one has to wonder if Q5 is needed at all (i.e., D1 connected directly to the supply rail).
However, someone apparently went to a lot of trouble to add the propagation delay and slow turn-on and even slower turn-off of Q5. Perhaps the slow turn on of Q5 following Q4 turn-off was needed to ramp-up Q6 turn-on through a linear region to ensure oscillation start-up.
The question I now have, after the pin 1 and pin 7 mix-up discussions, is whether it is actually intended that Q5 remain on for the longer period or if Q4 is to remain on for the longer period.
It would seem to me that the circuit would oscillate during the entire Q5 on/Q4 off period. Perhaps it is the Q5 on time that is intended to be the shorter time period, allowing the circuit to briefly oscillate by active means following a much longer period, when Q4 is turned on and Q6 is turned off and with an open collector, allowing these oscillations to ring down. If this is so, Q4 would be turned on for most of the time.
Someone let me know if I am not comprehending this correctly.
I originally thought that the drive coil was to be hit with just a quick pulse and then allowed to ring down. This circuit does not appear to do that. It would appear moreso to be a gated oscillator.
Are the outputs at J3 and J8 not being used at this time?
PW
« Last Edit: 2021-05-11, 18:07:37 by picowatt »
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