[AMRadio] re: Apache audio info; the REAL story

[manualman at juno.com]

Applies only to a stock Apache:

Apache manual dated 1959:

Page 7, paragraph 5: 
Two gain controls are provided in the Apache modulator. The audio gain
control (THIS IS THE FRONT PANEL CONTROL) between the first two stages of
the speech amplifier operates as a combined gain and CLIPPING CONTROL.
The level control (THE CONTROL BEHIND THE KEY JACK) serves to set the
100% modulation level. The gain control (front panel control) can be set
to give normal unclipped modulation by merely setting the peak input to
the clipper just at the threshold of clipping (  when the peak to peak
voltage of the audio signal exceeds approximately 6 volts, the diodes
(6AL5) conduct and prevent further increase in amplitude ). The level
control (behind the key jack) can then be set to give 100% modulation.
Thus, by further increasing the gain (FRONT PANEL CONTROL), the input to
the clipper is increased and more and more clipping can be introduced
without overmodulating the carrier due to the limiting action of the
clipper. 

Page 94, paragraph 8:
To test phone operation... and rotate the audio gain control (THE FRONT
PANEL CONTROL)  to the position that gives the amount of speech clipping
desired. With high impedance crystal or dynamic microphone, 10 percent
rotation of the audio control (THE FRONT PANEL CONTROL) will give 0 DB of
clipping, 20 percent will give 9 DB, 30 percent ....etc. The recommended
level of clipping for general communication is about 12 DB, which is
produced with about one-quarter of a turn from full CCW on the audio gain
control (THE FRONT PANEL CONTROL).

It's been that way in the manual for 43 years. You guys have come up with
some very creative and confusing dissertations on Apache audio.

Pete, WA2CWA

On Sat, 13 Apr 2002 19:40:54 EDT SBJohnston at aol.com writes:
> 
>  billsmith at ispwest.com writes:
> 
> >Not necessarily.  A clipper is a limiter.  A limiter need not 
> introduce
> >the severe distortion a "brick wall" diode clipper will contribute. 
>   :-)
> 
> That's true and you say it well:  "A clipper is a limiter."  If the 
> stage in 
> the Apache is a clipper, then the fellow who called it a limiter 
> isn't wrong. 
>  The control behind the CW key jack sets the drive to the stage 
> where the 
> peak-limiting is taking place.  Set the drive toward the low end and 
> you're 
> just clipping off the peaks that you don't readily hear.  Drive it 
> harder and 
> now you're tearing off nasty chunks of the waveform and you can 
> really hear 
> it.
> 
> I've always thought of a limiter as a device that reduces the peak 
> values of 
> a signal down toward the average level.  It can rip and tear those 
> peaks off 
> (simple back-to-back diodes) or it can gently smooth them off (as in 
> 
> sophisticated audio processing).
> 
> Some confusion can come in as some folks use the term limiter to 
> cover a 
> device that I know as a "compressor" which adjusts its gain to 
> maintain a set 
> average output level.  It has the effect of reducing the dynamic 
> range of the 
> signals applied.  But it doesn't peak-limit unless its action is set 
> fast 
> enough top respond to the transients - but then it is a limiter.
> 
> Words, words, words... sigh.   -grin-
> 
> 73  Steve
> 
> sbjohnston at aol.com
> 
> _______________________________________________
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> AMRadio at mailman.qth.net
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> 

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