I've been impressed with the operation of the Micor bi-level squelch circuit based on the M7716 IC. I use Micor Spectra-Tac receivers exclusively on 440, 902, 6 Meters and 222 MHz (VHF to 222 conversion) with excellent results. However, I am perplexed by 10 Meters. The Spectra-Tac squelch circuit doesn't work well at all. It squelches up on fading signals that aren't all that noisy and drops out for no apparant reason. It appears that the squelch is set too high, but it isn't. I've tried different audio/squelch modules, receiver boards and housings. Even the IMTS modification which defeats the short squelch tail doesn't help the situation. When a UHF reciever is substituted in place of the 10 Meter receiver, the squelch circuit works fine.
An old 25-30 MHz Motrac receiver, with its simple 3 transistor squelch circuit, works perfectly on 10 Meters. There are no problems with drop outs. The receiver squelch remains open well into the noise. This leads me to believe that the Micor bi-level circuit needs to be optimized for 10 Meters. Does anyone know of any component value changes in the Micor bi-level circuit to optimize operation on 10 Meters?
