Fisher TFM1000 pulse count detector-How does it work?
I'm trying to understand how the switch and pulse counter stage of the Fisher TFM1000 tuner works. I have read a copy of an article by A H Seidman from Electronics World Jan 1967. Attached is an LTspice file I have created in an effort to try to understand how the circuit works.
The first 3 limiter stages are straightforward. It is the switch, delay line and pulse counter that I don't understand (centre around Q5,Q6 and L3 in the LTSpice schematic). I have cross referenced the article above with the service manual and L3 is just marked 500 (it does not indicate nH,uH, or mH). However the photo of the unit shows a coil mounted on a ferrite rod. This could be the delay line. Could someone help me to figure this out? I'm just curious as to how this novel detector works. Thanks.
PS Please change the file extension on the attached txt file to .asc .It is the LTSpice schematic. The pdf file is a page from the service manual with the limiter/detector schematic. The article mentioned above is too large to upload. Please do a search of American Radio History to read it.
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