The Orions use the Analog Devices SSM2166 as a mic preamp and AGC, which can
be driven with inputs of up to 1,000 mV with distortion of just over 1%, so
it would be very hard to cause distortion in the first stage of audio unless
a high-level output was used to drive the mic input. See the charts at:
http://www.analog.com/UploadedFiles/Data_Sheets/83095497SSM2166_b_.pdf
Also, there is a gain control at the mic input, located on the underside of
the case, just behind the mic connector.
I agree with Carl that the best audio can be achieved with the ALC just
starting to flash, however I have found that going far beyond that point
does not create a lot more distortion. The "problem" O2's that were tested
on air used various levels of input audio, and they sounded just as bad to
my ears. The rest seem to sound good no matter how the input levels are
set.
Ron Castro
Chief Technical Officer
Results Radio, LLC
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
To: <tentec@contesting.com>
Sent: Wednesday, April 05, 2006 9:05 AM
Subject: Re: [TenTec] The Bug
If the mic gain in the radio isn't AT the connector but is after a stage
or two of audio, that first stage can be easily over driven by the
external equalizer leading to distorted audio that radio settings won't
cure.
100 Hz audio will be rejected by my receivers that roll off at about 300
Hz and so is again wasted energy. The original gurus of SSB, Papenfuse,
Bruene, and Shoeneke, said roll 'em off at 300 Hz (partly because the
analog filter slope also is relatively gentle and the added attenuation
of putting the carrier 20 dB down the slope helps need carrier
suppression specs) because you don't need lower frequencies for
communications. Ma Bell did that for long lines as well as for handsets
for most of the last century. And so most receiver designers working
from those tomes and resources roll off below 300 Hz and those
transmitting them are wasting energy. And those with receivers set for
communications bandwidth don't notice the extra basso profundo spectrum.
Yah, I know that spectrum is the basis in trade of the broadcaster, but
ham radio is communications, not broadcasting. AM BC stations run excess
basso profundo voice to compensate for 2" speakers in transistor radios
and AC/DC table radios. When AM receiver audio gets to a good speaker
its boomy, excessively bassy. And still doesn't help understanding.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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