Re: mc-3357 & mc-3359 squelch circuit Many receivers used the two mentioned chips... in both commericial, Amateur Radio and classic scanner circuits. I've seen both part numbers converted to "tk" numbers in Yaesu and Uniden Radios.
There are a number of working squelch circuits using the back end section of the chip with and without external op amps. While the Hamtronics circuit is/was rather basic it did work pretty well and was easy to experiment with changes/mods. A faster pussycat version of the same circuit can be found in the Spectrum, some (if I remember right) older Maggiore or Melco and Icom Repeater Receiver circuits. External op amp sections were added as gain buffers and high speed switches to enhance the internal circuit operation. The Hamtronics transistor hysterisis circuit works ok so don't discount it as a bad design. The receiver is/was a very basic circuit and could be used in modest low power repeater operation without a lot of grief. If you really were interested in more work with the mentioned chips I can and would be happy to email you some circuit diagrams and manuals related to the chips used in quality well engineered designs/circuits (in pdf file format). As in our poor mans repeater project... sometimes when money is tight you try to use whatever you can get you hands on. cheers, skipp > > No schematic handy here. It was the stock squelch circuit in a > > mid-80's vintage Hamtronics R144 or whatever "repeater grade" > > RX they were selling at the time. The noise filter was a simple > > 2-pole BPF with a very high Q. The op amp they used was the > > dedicated op amp within the MC3357 or MC3359 IF amp > > detector-on-a-chip. Nothing wrong with the op amp, just the > > circuit design around it. > > Roger. > > http://www.hamtronics.com/pdf/Manuals/R144-older.pdf > > may be what you were working with. A transistor for hysterieses > just rases a number of suspicions. I learned to stop trusting > built into IF chip squelch systems when I worked on a Regency > repeater many moons ago.
