Alex, You most likely need to change a few resistors and maybe a cap or two in the squelch circuit of the SpectraTac's A/S card. The components will be near the M7716 chip. If I recall correctly, some of the parts involve the chip's timing, while others tailor the discriminator audio to compensate for the variations in white noise between the bands.
A few years back I took a 70MHz SpectraTac chassis and replaced the 70MHz RF/IF board with a 147MHz receiver, and I had the opposite effect - before modification, the squelch would be extremely loose, and almost never go into the short tail mode. I changed a few resistors and caps to the appropriate band-specific values, and it began working like a regular Micor A/S board. The best thing would be to try and dig up one of the paging " Spectra-Tac Receiver" manuals that used to come with some of the paging stations. This one manual contained the tech docs for almost every band version RF/IF board, and the various versions of the corresponding A/S boards. If I recall correctly, there were three or four versions of the Spectra-Tac A/S boards - one for low band, one for VHF/UHF, and one for 800/900. If the values for the 70MHz mid-band version don't quite fix it entirely, simply compare the difference in values between the VHF and mid-band versions, and you should be able to calculate the appropriate values for low band accordingly. If you have trouble securing said manual, let me know and when I get back to my office, I'll see if I have an extra copy I can give you. Eric KE2D --- In [email protected], "kq2h" <k...@...> wrote: > > --- In [email protected], "Thomas Oliver" <tsoliver@> wrote: > > > Tom, the receiver and squelch appear to operate normally when using a service > monitor to generate signal. Noise floor issues can certainly be a problem, > although a Motrac receiver works fine on the same exact antenna. It's getting > blasted by the same noise... > > > > > I wonder if it is a noise floor problem. How does it act on a service > > monitor when it is not hooked to an antenna picking up high levels of noise? > > > > tom > > > > > > > [Original Message] > > > From: Adam Feuer <feuera@> > > > To: <[email protected]> > > > Date: 7/12/2009 7:30:11 AM > > > Subject: Re: [Repeater-Builder] Micor Bi-Level Squelch Circuit > > > > > > I am a very big fan of the Micor bi-level squelch. It's action is > > > second to none on my 440 and 900 system however, I too am having the > > > exact same problem on my 29.540 receiver in carrier squelch. I just > > > will not take anyone into the noise but rather near quieting signals > > > just "pop out" and disapear under the squelch. I have tried cleaning all > > > of the pins and swapping out the audio control module but nothing seems > > > to help. Interesting enough, this is NOT happening on my 6 meter Spectra > > > Tac! > > > > > > At the moment, I have placed my 29.540 Spectra Tac aside and replaced it > > > with a GE Mastr II auxiliary receiver on 10 meters. The results are > > > much better as pertains to the squelch, but this is not to start a Micor > > > vs. Mastr II comparison.....something is just not right on 10 meters > > > with a Spectra Tac receiver. If it can work on all of the other bands > > > (especially six meters!) it should work on 10. > > > > > > If anyone has any suggestions, perhaps some part changes on the audio > > > control module, they would be greatly appreciated! > > > > > > Adam N2ACF > > > > > > kq2h wrote: > > > > 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? > > > > > > > > > > > > > > > > ------------------------------------ > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ------------------------------------ > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > >
