[AMRadio] re: Apache audio Real good
russ dworakowski
wb3fau at hotmail.com
Wed Apr 17 11:56:41 EDT 2002
I did read it Pete, but I am real bad on searching out the
stuff, I have a condensed Heath manual that states the mismatch
in it. Tim WA1HLR also quoted that. But I do agree, you can
get pretty good results just by careful adjustment. I should make
that a project here, as i have 2 Apaches. The 1 is modified and the
other is all stock. Most that I have heard
just coming back on the air [from resurection] sound poor at best.
If not very distorted, they are very resticted in freq.
response. 73s Russ
>From: manualman at juno.com
>Reply-To: amradio at mailman.qth.net
>To: amradio at mailman.qth.net
>Subject: Re: [AMRadio] re: Apache audio Real good
>Date: Sun, 14 Apr 2002 18:04:56 -0700
>
>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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