w9mwq wrote:
>I have set the deviation level of the repeater to 4.5 Khz, which for
>most users is excellent, however I have a few users whom no matter
>what radio they use, alwys clips well over 6 Khz wide. Is there a way
>to limit this?
>
What exactly are you wanting to limit? The level of the deviation, or
the loudness of the user? While one would think a simple circuit would
do both, it isn't that simple. Loudness is a perceived thing. I have
seen Icom IC-2AT's set for 3.5 kilohertz deviation that "sound" louder
than an Azden 6000 set at 6 kHz. The reason is the amount of
clipping/processing ahead of the modulator, and how hard the user is
driving that processing. Many Japanese radios have too much Mic gain.
These radios tend to be very loud, even to the point of severe
distortion. Some of these radios don't have a typical "Mic Gain"
control, my Kenwood 742A is one such radio. My voice is loud, and my
habit is to hold the mic close and talk directly into it. I have had to
incorporate a mic gain control in most of my radios to tame down the
loudness. Again, the "deviation" was not at fault, it's the amount of
processing ahead of it that was the culprit.
Limiting the maximum deviation in a repeater is simple, overdrive the
mic input of the TX radio (to insure it is into clipping/limiting) and
set your deviation adjustment for whatever you want your max. deviation
at (like 5 kc) Then, reduce the input to the exciter (with the mic gain
control) so a 1:1 deviation is obtained. 1 will equal 1, 2 - 2, 3-3,
4-4, 5 will be a little less than 5 and 6 will likely equal 5.
>When these users come in, you have to turn down the volume, but then it's
>difficult to hear the normal voice users of the
>system. Any thoughts. Or am I just plagued with loud voice users.
>
>Mathew
>
Simple audio processing will not control perceived loudness. In this
instance, fixing the users radios or more complex audio processing is
needed.
Fixing the users radios is the best choice, but other more complex
solutions are out there. For more on that, I suggest you read this:
<http://www.repeater-builder.com/tech-info/audioprocessing.html>
Kevin Custer
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