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Stryker SR-94HPC Noise Blanker and AMC

Discussion in 'CB and Export Equipment and Accessories' started by Shockwave, Oct 13, 2018.

  1. Shockwave

    Shockwave Sr. Member

    Joined:
    Sep 19, 2009
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    Has anyone else noticed that that NB switch on this radio acts exactly like an Automatic Noise Limiter? As soon as you turn it on, it changes the sound of everything in the receiver. You hear a drop in high frequency response and a slight bit of distortion associated with the clipping action of the limiter. I have never been able to measure a reduction in impulse noise level on the S-Meter and the only effect appears to be AF rather than any blanking in the RF front end.

    Also curious if any mod for the expansion of the AMC range has been posted yet or if that's still being kept a secret? It has one of the most restrictive AMC circuits I've seen where it's constantly active, restricting the PEP output to a preset level rather than only being active on audio peaks. The radio can easily hit the 45 watts PEP when that circuit is only active to prevent distortion on louder audio peaks.

    In another thread someone asked about the frequency response of the AM transmitter. That's one nice thing about buying a cheap radio with the option of PL encoding. That audio circuit has to be able to pass the very low frequency PL tone and they didn't add the extra filtering in the mic line to restrict it back down to "Communications grade" audio. That provides some impressive bass response and the treble is just as strong. That may be another reason the audio limiter is so restrictive. Otherwise the low end in your audio could easily cover up the PL tone.

    The fact this rig uses an electret mic opens up some nice pre-amp options. Motorola made a handheld mic that was able to insert a single stage transistor pre-amp between the electret element and the audio line from the radio supplying the bias voltage to the element. That transistor and a few supporting parts can be added "dead bug" style to the back of the stock mic board with a little copper shield over the parts to prevent RFI. Useful on many radios with this type of mic element. Power mic audio from the original mic with no battery.


     

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