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I was thinking the other day "I wonder what was actually happening"?

This was in the late 70's, a common among DXers and Contesters was a dirt cheap thing to do to make your signal just jump and stand out in pile-ups.

My particular setup.
Plain TR-4
AC-4 power supply
Shure 444 Mic.

Like the D-104 the Shure 444"s frequency response was incredible with all Drakes.

Now this is my question of what is actually happening. I'll say what the Modification was at the end.
But doing this "Mod" you can immediately see the plate amp meter being MUCH more aggressive,
jumping far higher than usual, so power is either higher or more "Full".

Listening on the air It had the exact sound of a processed signal made by a external speech processor
like the "Vomax" unit. but at a FAR cheaper cost. Adjusted for Inflation the Vomax today would cost $412.00!!!!

Looking at a scope it also seems to look just like the vomax signal. Still "Peaky" but fuller.

It did not sound distorted at all. Or the sound of a bad flat-topped signal.

But the "Punch" it had was incredible! To a S meter and to the "Ear"
it seemed pretty equal to like a modern rig running maybe up to 10 db of compression.

But it seemed "Clean" Never got a complaint about splatter or distorted signal,
?if anything you got compliments on how great the audio was.

I never even thought to try to figure out what this "MOD" was actually doing,
all I knew was it worked, and worked GREAT with never a hint of anything negative from anyone.

What was this "MOD"?? On the AC-4 Power Supply is a Jack for the ALC for when running with an amp.
This Jack is connected to the amp,,, well you all know what it is for.

But this "MOD" was simply inserting a shorted out RCA plug into that jack on the AC-4 shorting it out.

That's it!

The Drake Is now retired, But I got to wondering, has anyone else done this "MOD" from the 70's
and even maybe still does it today?

And even more what was actually happening?

Joe WB9SBD

It was done all the time back then. Just a spst toggle to short out the? ALC jack.? ?Then it looked like a solid green bar on the scope, instead of the typ 'xmas tree' pattern.?

Funny thing was, nobody bitched abt imd / splatter...go figure.?

Some folks in W6 land told me they pulled out one of the tubes, then cut off one of the pins, to do the same thing.?

Essentially, you turned it into an rf clipper, albeit, with no filter to clean up out of band imd products. A real RF clipper would have the 2nd filter. ( like the magnum 6 /? DX engineering RF clippers).?

The Vomax was just a split band audio clipper, with a filter for each of the 3 x bands.? Then the filtered ( and clipped) 3 x bands were? re-combined.??

With the? ALC jack shorted out, the mic gain became the RF clipping level control.? IF? you wanted some more talk power for some pile up, it worked good.?

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Thanks Jim,
But I remember someone looking at the signal on a Heathkit station monitor and while it was a fat Christmas tree it was far from a fully filled as you say green bar.

I wonder if anyone can do some scope image grabs of shorted vs open,

Joe WB9SBD

Yeah, you don't want to do that. We have enough trouble these days with dirty signals on the air. Don't add to it. Get an inline processor, SP75 or equivalent.

73

-Jim
NU0C

On Thu, 25 Apr 2024 08:58:25 -0500
"Joe WB9SBD via groups.io" <nss@...> wrote:

Thanks Jim,
But I remember someone looking at the signal on a Heathkit station
monitor and while it was a fat Christmas tree it was far from a fully
filled as you say green bar.

I wonder if anyone can do some scope image grabs of shorted vs open,

Joe WB9SBD

On 4/25/2024 7:08 AM, Jim VE7RF wrote:

It was done all the time back then. Just a spst toggle to short out
the? ALC jack.? ?Then it looked like a solid green bar on the scope,
instead of the typ 'xmas tree' pattern.

Funny thing was, nobody bitched abt imd / splatter...go figure.

Some folks in W6 land told me they pulled out one of the tubes, then
cut off one of the pins, to do the same thing.

Essentially, you turned it into an rf clipper, albeit, with no filter
to clean up out of band imd products. A real RF clipper would have the
2nd filter. ( like the magnum 6 /? DX engineering RF clippers).

The Vomax was just a split band audio clipper, with a filter for each
of the 3 x bands.? Then the filtered ( and clipped) 3 x bands were?
re-combined.

--

73

-Jim
NU0C

People must understand that the power distribution in speech is not very efficient. Thus speech processors. They do several things but all are to the end of modifying power distribution to make it more efficient in power limited transmission systems. Note that as a rule of thumb the ratio of peak to average in male speech is about 10db. If a transmitter is set to pass peaks without distortion its average output will be very low. A processor reduces the ratio of peak to average in various ways and also modifies the spectral distribution in the speech to accentuate the parts that contribute to intelligibility and articulation. An ALC is really a sort of peak limiter to reduce drive when it will drive the amplifier into distortion. Most ALC systems are fairly simple so an external processor is often more effective. With an external processor the ALC can be almost inactive but will provide a safety factor.
The idea is to increase average power to overcome noise. This also applies to the modification of the speech spectrum. Since low frequencies contribute the most to speech power but relatively little to articulation it is common to limit low frequency response and enhance high frequency response since the highs contribute most to it. However, the effect of combined spectrum shaping and amplitude limiting is not simple so some care must be applied in deciding what exactly to do.
There is a perfectly enormous amount of literature on speech processing (and music processing) in the technical literature. Bell Labs has research going back a century, worth doing some reading.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

?"Note that as a rule of thumb the ratio of peak to average in male speech is about 10db."

Most tech literature indicates 14.5 db.? Other literature indicates 21.5 db.? ?They call that crest factor.? ( peak to average ratio).

?

Point is, without basic ALC, your average power output on SSB would be through the floor.? ?That's assuming using just enough audio drive to? just drive the xcvr to say 100w pep out.? ?You can see that on any average reading wattmeter.
if u want true average, use an RF ammeter.?

?

I experimented? with my 6 x band digital compressor, and even with the rls times as low as 20 msecs, it works pretty good, but isn't like a RF clipper.? ?Done correctly, you can get globs of talk power....and zero distortion...and have no alc showing on the xcvr.? ? The problem with RF clipping is..... the filters only remove the out of band imd, and not in band imd...so there is a limitation there.? ?Another method is to use ALC, but with a much faster rls time constant.? Done right, that will be distortion free...and just as effective as rf clipping.? ? And any processing scheme will work at an optimum level if preceded by a good audio compressor.? You need to feed a constant level? into the device/xcvr etc.? With a boom headset, the mic is a constant distance from ur mouth.? To kill background noise pickup, either a gate, multiband gate, or downward expander is used.? ?A noise gate is just a high ratio downward expander.?

?

remember when? TV commercials came on....and just about blew u outa the chair ?? ?I looked at em on an SA....and what happened when the commercials came on,? is all the peaks dropped exactly .5 db? all the way from lows...to highs, (20 hz to 20k)... meanwhile the average increased by exactly 6.0 db...again right across the entire passband.? ? And that's on top of regular program material.?

?

With ham radio ssb, on RX, we have AGC.? ?S meters are peak reading devices....they won't depict average power.? On the old drakes, from S3? to 60 db over S9 only increased the audio output by a mere 3 db.? It's all squashed flat.

And no, I don't advocate shorting out the alc on drakes. Back then, gear was expensive as is.

On 2024-04-26 09:35, Jim VE7RF wrote:

I experimented with my 6 x band digital compressor,

*** Is that something you bought? Or something you made?
I've played with audio with a PJRC Teensy 4. They have an audio
design tool on their website; you drag and drop mixers, filters etc,
and it creates a skeleton "C" program to implement it.

I used that to create a CW filter/translator for my KWM-2, which
is horrible for CW as is - because the sidetone & received signal are
1750Hz. I mix it down to 650Hz and do some serious audio filtering.
All in software.

- Jerry, KF6VB

ALC was never intended to be a speech processing system. Undesirable things happen when you try to do that. I point (again) to SM5BSZ's work in this.



73

-Jim
NU0C

On Fri, 26 Apr 2024 09:35:13 -0700
"Jim VE7RF via groups.io" <jim.thom@...> wrote:

"Note that as a rule of thumb the ratio of peak to average in male speech is about 10db."

Most tech literature indicates 14.5 db.? Other literature indicates 21.5 db.? ?They call that crest factor.? ( peak to average ratio).

Point is, without basic ALC, your average power output on SSB would be through the floor.? ?That's assuming using just enough audio drive to? just drive the xcvr to say 100w pep out.? ?You can see that on any average reading wattmeter.
if u want true average, use an RF ammeter.

--

73

-Jim
NU0C

On Fri, Apr 26, 2024 at 07:27 PM, jerry-KF6VB wrote:

I experimented with my 6 x band digital compressor,

*** Is that something you bought? Or something you made?
I've played with audio with a PJRC Teensy 4. They have an audio
design tool on their website; you drag and drop mixers, filters etc,
and it creates a skeleton "C" program to implement it.

I used that to create a CW filter/translator for my KWM-2, which
is horrible for CW as is - because the sidetone & received signal are
1750Hz. I mix it down to 650Hz and do some serious audio filtering.
All in software.

- Jerry, KF6VB

##? Nope.? I bought a behringer 9024? 6 x band digital compressor.? Rack mount. I had 3 of em at one point.? The 6 x bands are nose to tail, no gaps....and a max of 20 hz to 20 khz.?

For ham radio use, essb, etc, the 6 x bands are typ programmed for aprx 50-200 hz, 200-800 hz, 800-1600 hz, 1600-3000 hz, 3000-4500 hz, 4500-6000 hz.? ( Or any combo u want, but u gotta use up all 6 x bands).? Each band has separate compressor controls, each has it's own noise gate etc.? You could spend months and months playing with it.

##? to get any of it sounding correctly, u 1st have to do some serious eq'ing.?

On Sat, Apr 27, 2024 at 02:18 AM, Jim Shorney wrote:

ALC was never intended to be a speech processing system. Undesirable things happen when you try to do that. I point (again) to SM5BSZ's work in this.



73

-Jim

##? read it several times, eons ago.? I have two FT-1000D's.? Basically, before u turn the RF clipper on,? you 1st adjust the mic gain for XXX? alc action.? ?Trying to maintain XXX? alc action requires an outboard audio compressor...to maintain a constant audio level going into the xcvr.? Otherwise, clipping level will be a function of how loud u talk.? ?Then with clipper on, dial up XXX db of rf clipping.? Note, the analog meter in the FT-1000D reads average, not peak, so when the meter sez.... '10 db clipping'? it's actually 20 db of rf clipping.? (The analog meter only reads peaks when on RX, that's it).? So along comes joe ham, tweaks the clipper for 15-20 db of clipping, then ends up with 30-40 db of clipping.? Manual sez no more than 10 db of clipping, as indicated on the average reading meter ( which is actually 20 db of clipping)

## once RF clipping level is tweaked, meter is switched back to read ALC.? ?Then the OUTPUT control is tweaked so that you have the same ALC action, or less....than you had with clipper off.? ?With a quality (IE: rack mount pro-audio, professional audio compressor) feeding the xcvr, and clipper on, the output control on the yaesu can be tweaked for very little alc action, just a miniscule amount is required.? ?At that point, you can have all the clipping you want, with minimal output alc action...and no alc artifacts.??

?

## old guy north of me, had a FT-1000D, and never did get it through his head how to adjust the clipper.? He would have the clipper on, see the alc was on the low side, then proceed to crank up the mic gain...which is exactly what u don't want to do.? By turning up the mic gain, the clipping level just went way up. What he shoulda been doing is to tweak the clipper output control, to adjust the alc.? ?I showed him several times...then gave up.?