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955hpc question

Discussion in 'CB and Export Equipment and Accessories' started by Jim1428, Oct 4, 2018.

  1. Jim1428

    Jim1428 Member

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    The mike gain control on my 955hpc only works up to the half way point, when I turn it past the 12 o'clock position there is no further effect on the gain.



    Is this normal? If any 955 owners could check their radios I would greatly appreciate it.
     

  2. Ranch55

    Ranch55 Well-Known Member

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    Can you please explain how you are determining the increase in gain, and the lack thereof after the half way point.
     
  3. Jim1428

    Jim1428 Member

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    I noticed it when trying to set modulation. I turn the mike gain to max then set modulation to 100%, when I go back and check modulation level using the mike gain it reaches 100% at the 12 o'clock position.

    I am feeding a 30mv 1250hz audio signal in and using an oscilloscope connected to an rf demodulator to monitor the output.
     
  4. nomadradio

    nomadradio Analog Retentive

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    This is the job of the modulation limiter.

    Once you reach the limit, increasing input level has no effect.

    73
     
    rabbiporkchop likes this.
  5. Jim1428

    Jim1428 Member

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    Seems a bit strange to me, most other radios I am familiar with allow you to use the entire range of the mike control.

    I wasn't sure if there was a problem with the radio or my procedure was incorrect.

    Thanks for the reply.
     
  6. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Well, hold on...

    There are interpretations to this...

    One being, the audio level may stay the same - but only if you are using signal tones - not voice.

    IF you use voice - and have a fan running in the background (work with me here - the example). Then, for starters, and the Mic gain is say at - only 1/4 the way up (25%) the pickup will be mostly from the voice. But, as you increase the mic gain and the Mic element is not a noise cancelling one - you'd have that fan coming in with you "COMPRESSING" into the audio line to the radio...the audio "level" may not go up but the audio PRESENCE of what the mic element picks up, certainly does...

    Now, if the Mic gain control being analog is not right - you can have a "tonal effect" which is a lot like you'd get in R/C series circuits - meaning - if the "pots" ground lead is open - the resistive element of the pot then becomes part of a tonal filter...the "C" part is the blocking cap to transfer audio from the mic Gain circuit into the mic amp and limiter sections.

    You start out with a "thin" bodied- but weak signal - (Full resistive element) that changes volume to a given level then little else - but Tonal effects are more pronounced. Onto even a more bass boost effect until the radios own processing filters start to pare down and peak the spectrum at a given bandwidth.

    You may not notice the effect because the limiter as well as the bandpass is kicking in to trim the mics audio.
     
  7. Jim1428

    Jim1428 Member

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    Thanks for your reply.
     

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