[AMRadio] re: Apache audio Real good


manualman at juno.com manualman at juno.com
Sun Apr 14 21:04:56 EDT 2002


Russ:
I'm curious as what Apache manual you're reading. I can't find any
reference to where Heath engineers intentionally mismatched the
modulation transformer to force more audio through it. Are you refering
to the fact that they designed it for class AB2 audio or some other
evidence. See page 7, paragraph 7 of the manual: "The modulation
transformer provides the proper match between the modulator output
impedance and the load impedance."

With a good high impedance microphone, and proper adjustment of the front
panel gain/clipper control, and the modulation level control behind the
key jack, the "tons of distortion and splatter" you mentioned doesn't
happen. Ovidously cranking up the front panel "gain" control, if you
didn't know that it was really the clipper control, could turn the
transmitter into a spatter machine. 

FYI: During the past winter months, I spoke to three different stations
on 10 meters who were running Apache's. None of them knew anything about
the modulation control behind the key jack. They all thought the front
panel "gain" control was the only audio adjustment they had.

Pete, CWA

On Sun, 14 Apr 2002 16:42:49 -0400 "russ dworakowski"
<wb3fau at hotmail.com> writes:
> Yes,  you  can  leave  the clipper  in place,  But  it still 
> distorts
> the  audio  down  at  low settings.  Read  the  book on  the  
> Apache,
> it tells  how  they  intentionally  mismatched  the  mod  tranny  in 
>  hopes  
> of  forcing  thru  more audio.  But  it  produced  tons  of  
> distortion and  
> splatter.  Remember  this  rig  and  the Valliant  were
> the  last efforts  to  save  AM and  plate  modulation.  It  was 
> not
> well  done in  original form.  The  Apache  and  the Valliant  are   
> both  
> great AM  rigs  with  the  correct  mods  done.  Russ
> 
> 
> >From: "Bill Smith" <billsmith at ispwest.com>
> >Reply-To: amradio at mailman.qth.net
> >To: <amradio at mailman.qth.net>
> >Subject: Re: [AMRadio] re: Apache audio not good
> >Date: Sat, 13 Apr 2002 17:28:42 -0700
> >
> >Yes, that is how I understand it.  Understanding the difference 
> between a
> >"compressor" and "limiter" is difficult, because they do almost the 
> same
> >thing.  I think the real distinction is that a limiter is a device 
> used as
> >the last processor before a transmitter's modulation stage.  The 
> limiter is
> >in position to make sure the transmitter is never overmodulated.   
> This is
> >particularly important in FM transmitters because they can 
> splatter, or
> >excessive modulation can exceed the bandpass of the receiver and 
> activate
> >the receiver's squelch circuitry.
> >
> >A compressor adjusts the audio path to provide the largest average 
> signal,
> >and is in position to provide maximum "punch".  Usually the 
> difference
> >between a limiter and a compressor is a matter of a longer 
> time-constant
> >used in the voltage-controlled amplifier stage that is 
> automatically
> >adjusted to control the volume.  A compressor will usually not 
> fully 
> >respond
> >to a strong, very loud pulse, or a "rogue" pulse (similar to a 
> "rogue wave"
> >at an ocean beach).
> >
> >A simple "brick wall" limiter can be made from a couple of LED 
> diodes, 
> >wired
> >back to back.  Positive audio peaks will light one LED, and 
> negative audio
> >peaks will light the other LED.  One can soften the limiting action 
> 
> >somewhat
> >by placing resistors (or a pot) in series with each LED diode, with 
> a diode
> >wired across each pot so that the resistance is effective for only 
> one
> >polarity.
> >
> >The advantage of LED's is they will light when they are limiting 
> (the
> >circuit is low-impedance).  The problem, of course is that severe 
> limiting
> >occurs when the diodes conduct.  But the circuit provides a concept 
> of how 
> >a
> >limiter operates, and the pots can be adjusted to provide 
> asymmetrical
> >(positive peak) limiting.
> >
> >73 de Bill, AB6MT
> >billsmith at ispwest.com
> >
> >
> >
> >
> >----- Original Message -----
> >From: <SBJohnston at aol.com>
> >To: <amradio at mailman.qth.net>
> >Sent: Saturday, April 13, 2002 4:40 PM
> >Subject: Re: [AMRadio] re: Apache audio not good
> >
> >
> > >
> > >  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
> > > http://mailman.qth.net/mailman/listinfo/amradio
> >
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