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Author Topic: Lowering output power from SB200  (Read 14493 times)
N3JBH
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Posts: 2358




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« Reply #15 on: February 25, 2009, 03:50:52 PM »

"Article forthcoming! With detailed explanation and signal analysis showing clearly why turning down the mike gain is not a good idea."

Cool Steve i really enjoy your great articles... I love to see what your tlking about and see it explained like you do it,,, Jeff
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WB4JZY
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Posts: 76




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« Reply #16 on: February 25, 2009, 03:51:45 PM »

In the context of generating a SSB signal and following that with stages of linear amplification, I stand by the fact that varying the audio level (read mic gain) absolutely varies the power output.  If you want to qualify that by taking a basic ssb generator and add to it dsp, compression, feedback, alc, a microprocessor and whatever else,  well thats another story.
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K5MBV
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Posts: 265




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« Reply #17 on: February 25, 2009, 03:59:34 PM »

"It allows the ALC to still work properly and provide full modulation with a high average-to-peak ratio when running reduced power, which can never be achieved by "turning down the mike gain.""

Actually it can be achieved ...by turning OFF the ALC which is NOT the subject of this thread anyway. If you
like good intellegible audio, don't even use ALC (ALC reduces dynamic range causing its own distortion.) The
signal would look fine on a scope, but it would be compressed. The average power would be slightly higher
and the audio slightly muffled.

Just turn the mic gain down.

Ken  K5MBV
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KE7VOB
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Posts: 22




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« Reply #18 on: February 26, 2009, 09:49:22 AM »

There is no provision for turning alc off on this radio.

The manual states that this rig does 100 watts ssb at all times. Nowhere in the manual does it state how to reduce power by reducing mic gain. It says to adjust mic gain to keep voice peaks within the alc scale for proper modulation and that is all.

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KE7VOB
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Posts: 22




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« Reply #19 on: February 26, 2009, 09:49:58 AM »

Also looking forward to an article from Steve!
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WB2WIK
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Posts: 21837




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« Reply #20 on: February 26, 2009, 11:07:22 AM »

>RE: Lowering output power from SB200       Reply
by K5MBV on February 25, 2009    Mail this to a friend!
"It allows the ALC to still work properly and provide full modulation with a high average-to-peak ratio when running reduced power, which can never be achieved by "turning down the mike gain.""

Actually it can be achieved ...by turning OFF the ALC which is NOT the subject of this thread anyway.<

::How do you turn off the ALC?  I don't own any transmitters that allow you to do that.  In fact, in every transmitter I own, if you went inside to manually disconnect the ALC, the transmitter would no longer transmit.

>If you
like good intellegible audio, don't even use ALC (ALC reduces dynamic range causing its own distortion.)<

::See above.  Impossible.

>The
signal would look fine on a scope, but it would be compressed. The average power would be slightly higher
and the audio slightly muffled.

Just turn the mic gain down.

Ken K5MBV<

::Turning the mike gain down runs the transmitter with a "ceiling" of full output power, whatever that is, and completely uncontrolled.  And that's an engineering fact, not an opinion.  You can't disconnect the ALC in any transmitter I know of, certainly none of the ones on the market today.

So what happens when you turn down the mike gain is this:

You reduce the average output power by undermodulating all stages; that wouldn't be bad, except that the transmitter's "ceiling" can still be reached easily with the occasional voice peak or anything that spikes the modulator.  That peak will be just as high as if you did not turn the mike gain down, unless you turn the gain all the way "off," so there's no modulation at all.

So what you end up with is a completely uncontrolled transmitter with low average output power but as much peak envelope power as you had before you turned the gain down.  Not an opinion, an engineering fact.

I have several HF transmitters made by Drake, Kenwood, Ten Tec and Yaesu.  Every one of them behaves exactly as I described above.  On a "wattmeter," the power will look lower.  On a scope, or even a good true PEP wattmeter (with a peak sample and hold detector circuit that must be active and powered to be functional), the PEP power remains the same whether the mike gain is turned up very high or down very low, until the gain is turned all the way OFF and there's no modulation at all.

This is a crappy way to modulate a transmitter.  It reduces readability and doesn't allow the transmitter to operate as it was designed to do.  You will NOT find "if you want to run less power on SSB, just turn the mike gain down" as an instruction in ANY user manual for an SSB transmitter.

20+ years ago, most manufacturers added a new control to the front panel of their rigs: POWER.  That control is not a second "mike gain," it's an ALC level adjustment that operates within the ALC loop.  When you turn it down, it turns down the power "ceiling" of the transmitter, so occasional voice spikes will not exceed the output power level of whatever you preset with the POWER output level control.  That's perfect, and it's a control that should have been in all SSB transmitters going back to the "beginning."  But most just woke up in the early 1980s or so to add this feature.

WB2WIK/6
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K5MBV
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Posts: 265




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« Reply #21 on: February 26, 2009, 01:03:24 PM »

ALC= Compression= Distortion

ALC makes the appliance put out slightly more average
power by compression. Great for those who like this
slight increase at the cost of distortion. Great  gimmick intended for the appliance operator.  

Ken K5MBV
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WB2WIK
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Posts: 21837




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« Reply #22 on: February 26, 2009, 01:08:47 PM »

>RE: Lowering output power from SB200       Reply
by K5MBV on February 26, 2009    Mail this to a friend!
ALC= Compression= Distortion

ALC makes the appliance put out slightly more average
power by compression. Great for those who like this
slight increase at the cost of distortion. Great gimmick intended for the appliance operator.

Ken K5MBV<

::Ken, you're firing at shadows.  Do *you* have an SSB transmitter where you can turn "off" the ALC?  There aren't any on the market like that.  ALC is the entire control loop for the transmitter, including the circuit that provides SWR protection, overdrive prevention, output power adjustment, and everything good that transmitters have.

ALC was included in the Collins S-line transmitters designed in the 1950s, and it's been with us ever since.

WB2WIK/6
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K5MBV
Member

Posts: 265




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« Reply #23 on: February 26, 2009, 01:17:37 PM »

I do not use ALC with any of my amplifiers and operate
the transceivers at power levels below ALC operating
levels. The transceivers have power controls which I
use. If they did not, I would use the mic gain to turn
down the power as I have done for many years with
radios that had no ALC. I like clean audio.

Ken  K5MBV
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WB4JZY
Member

Posts: 76




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« Reply #24 on: February 26, 2009, 03:34:51 PM »

wik

What you are saying is simply not true.  I have an IC-735, HW-100, HW-32 and 2 homebrew ssb exciters and a peak reading wattmeter.  I can adjust the SSB power output of ALL of them with the mic gain control.
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K4TLJ
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Posts: 94


WWW

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« Reply #25 on: February 26, 2009, 06:44:08 PM »

As I recall one of the questions on the General exam asks how to control power on a SSB rig. Answer was 'mike gain'. From memory did not check the question pool.
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WB2WIK
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Posts: 21837




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« Reply #26 on: February 26, 2009, 07:12:54 PM »

>RE: Lowering output power from SB200       Reply
by K5MBV on February 26, 2009    Mail this to a friend!
I do not use ALC with any of my amplifiers and operate
the transceivers at power levels below ALC operating
levels. The transceivers have power controls which I
use. If they did not, I would use the mic gain to turn
down the power as I have done for many years with
radios that had no ALC. I like clean audio.

Ken K5MBV<

::Ken, you are still shadow boxing here.  Here's why: I am not talking about, and never did talk about, any ALC connection to an amplifier.

I am discussing the ALC inside your transmitter, which is always there, always active, and you cannot defeat even if you want to.

ALC is part of every SSB transmitter manufactured.  This has NOTHING to do with amplifiers.

WB2WIK/6
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WB2WIK
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Posts: 21837




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« Reply #27 on: February 26, 2009, 07:21:14 PM »

>RE: Lowering output power from SB200       Reply
by WB4JZY on February 26, 2009    Mail this to a friend!
wik

What you are saying is simply not true. I have an IC-735, HW-100, HW-32 and 2 homebrew ssb exciters and a peak reading wattmeter. I can adjust the SSB power output of ALL of them with the mic gain control.<

::And you received your engineering degree from ______?
(Please fill in the blank.)

You're being silly.  Of course you can adjust SSB power down with the mike gain control, I never said you couldn't.  Just that it's the wrong way to do it, because you leave the ALC loop in your transmitter hanging without any control.  Very bad idea, leads to poor modulation quality, spiky audio, no "punch," and lots of bad side-effects.

Hey, I can turn my transmitter OFF if I want to reduce power, that works, too.  But it's not the goal.  The goal is generally to reduce power and also sound good.  You cannot do that by turning down the mike gain.

WB2WIK/6
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K5MBV
Member

Posts: 265




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« Reply #28 on: February 26, 2009, 08:06:19 PM »

Turning down mic gain can improve audio quality.

Using ALC or any other compression method to get
more "punch" results in distortion because it reduces
dynamic range.

Not saying it's a bad thing. It actually can keep careless
operators from overdriving the amplifier and
causing distortion resulting in increased bandwidth.

Ken  K5MBV
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WB4JZY
Member

Posts: 76




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« Reply #29 on: February 26, 2009, 08:34:51 PM »

wik
" That peak will be just as high as if you did not turn the mike gain down, unless you turn the gain all the way "off," so there's no modulation at all."
This what you said, its silly and its wrong.
Before you question my credentials, you should take a moment to review basic SSB theory.
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