Re: [Elecraft] ALC implementation

[K9MA]

I like to think of ALC as receiver AGC in reverse. Done properly, it 
results in minimal distortion while keeping the signal level nearly 
constant.  As far as I can tell, commercial transceivers have all been 
doing this pretty well for a long time.


What I've never been able to figure out is why it's so hard to close the 
ALC loop around an external amplifier. If it works with the 100 W 
amplifier built into the transceiver, why won't it work with a bigger 
amplifier? (And it seems about universally agreed that it won't.)


73,
Scott K9MA


On 7/12/2019 23:32, Wes wrote:
You do know that the K3(S) uses a slow ALC system for power control 
don't you?


Wes  N7WS

On 7/12/2019 8:53 PM, Brian Denley wrote:
Nothing when that’s what you want.  But using ALC to control xcvr 
power is uncontrolled compression that may or may not be desired.


Brian
KB1VBF
Sent from my iPad


On Jul 12, 2019, at 4:09 PM, Wes  wrote:

And what exactly is the problem with compression?  It's used all 
over the place.


Wes  N7WS


On 6/28/2019 11:38 AM, Brian Denley wrote:
I have always thought that ALC is not appropriate for power 
control.  It’s a protection system.  Over use of ALC acts like 
compression.  No?


Brian
KB1VBF
Sent from my iPad
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--
Scott  K9MA

k...@sdellington.us

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Re: [Elecraft] ALC implementation

[Ian White GM3SEK]

The original concept of ALC was devised by Collins engineers as part of 
their development program for speech processing. Speech clipping 
flattens the peak amplitude, but also introduces some splatter which 
then has to be filtered out - but the filtering re-introduces a small 
amount of level variation (called 're-peaking'). Collins then added a 
very small amount of ALC, only 2-3dB, to keep the peak envelope power 
more constant. This mild ALC introduced very little additional splatter 
of its own, so the result was a large increase in intelligibility with 
very little increase in bandwidth.


Where ALC got a bad name was when other manufacturers started mis-using 
it for other purposes - in particular for manual power control from 100W 
down to 1W or less. ALC was also being used to compensate for variations 
in TX gain between different bands. All of this required much more gain 
in the control loop (20-30dB) which made teh ALC much more aggressive 
and created major problems with transient behavior - in other words, 
quite serious splatter due to the ALC system itself.


Then someone decided it would be a good idea to apply ALC from the power 
amplifier, thus wrapping an external control loop around the existing 
ALC loop within the transceiver, so the transient behavior became 
totally unpredictable. Add to this the tendency of many hams to 
perpetually overdrive their transmitters while *also* applying speech 
processing, and the result was that both ALC and speech processing got a 
very bad name.


Enter the K3. With a little persuasion from early adopters, Elecraft 
returned to the original Collins concept of applying only a small amount 
of ALC to minimise re-peaking *without* significantly re-introducing 
splatter. The SDR concept allowed other means to be used to implement 
the non-dynamic power control functions such as manual power setting and 
TX gain compensation. When correctly configured according to the User 
Manual, the K3 family of transceivers are capable of excellent speech 
processing without worrying about also creating splatter. (Also note 
that speech processing is automatically disabled for data modes.)


As far as I know, there is still no other manufacturer who is doing this.

References:

[1] W E Sabin and E O Schoenike (Collins), 'Single-Sideband Systems and 
Circuits'. McGraw-Hill Book Company 1987. ISBN 0-07-054407-7


[2] Leif Åsbrink, SM5BSZ (http://sm5bsz.com), ‘Real Life Dynamic Range 
of Modern Amateur Transceivers’ and ‘Speech Processing for SSB 
Transmitters’.


73 from Ian GM3SEK


On 13/07/2019 08:35, Richard Corfield wrote:

The compression modulates the signal. That will have a fourier transform of
its own. If we think of it as a simple amplitude modulation then, as for AM
signals, the spectrum of the original signal will be combined (convolved)
with upper and lower sidebands representing the spectrum of the compressor.
Our ears don't notice (unless we're sound guys listening to a pop song
thinking "They've squashed those dynamics to death" ;-) ) but maybe a
digital mode will.

The transmitted signal is constrained to the IF passband so you stay within
band. The compression frequencies and hopefully amplitude are both small so
the artefacts it introduces into the spectrum should also be both narrow
and small.

  - Richard



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Re: [Elecraft] ALC implementation

[Ian White GM3SEK]

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Re: [Elecraft] ALC implementation

[Richard Corfield]

The compression modulates the signal. That will have a fourier transform of
its own. If we think of it as a simple amplitude modulation then, as for AM
signals, the spectrum of the original signal will be combined (convolved)
with upper and lower sidebands representing the spectrum of the compressor.
Our ears don't notice (unless we're sound guys listening to a pop song
thinking "They've squashed those dynamics to death" ;-) ) but maybe a
digital mode will.

The transmitted signal is constrained to the IF passband so you stay within
band. The compression frequencies and hopefully amplitude are both small so
the artefacts it introduces into the spectrum should also be both narrow
and small.

 - Richard


On Fri, 12 Jul 2019 at 22:01, Wes  wrote:

> What distortion?
>
> On 7/12/2019 1:15 PM, Jim Rhodes wrote:
> > Nothing when it is done correctly on a mode that can stand the
> distortion. I
> > personally won't use it on digital modes as my rigs tend to turn it off
> by
> > default.
> >
> > Jim Rhodes
> > K0XU
> >
> > On Fri, Jul 12, 2019, 15:10 Wes  > > wrote:
> >
> > And what exactly is the problem with compression?  It's used all
> over the
> > place.
> >
> > Wes  N7WS
> >
> > On 6/28/2019 11:38 AM, Brian Denley wrote:
> > > I have always thought that ALC is not appropriate for power
> control.
> > It’s a protection system.  Over use of ALC acts like compression.
> No?
> > >
> > > Brian
> > > KB1VBF
> > > Sent from my iPad
> >
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Re: [Elecraft] ALC implementation

[Brian Denley]

Wes:
Yes but I assume you have have used or use other xcvrs as well.  As a general 
comment, that doesn’t change the idea that using ALC to control a xcvr’s power 
to one’s linear isn’t the purpose of ALC and would seem to not be a very 
healthy practice.   If one were to choose that path, then one should be mindful 
that the result acts much like compression.  In some cases, lots of compression!

Brian Denley
KB1VBF
Sent from my iPad

> On Jul 13, 2019, at 12:32 AM, Wes  wrote:
> 
> You do know that the K3(S) uses a slow ALC system for power control don't you?
> 
> Wes  N7WS
> 
>> On 7/12/2019 8:53 PM, Brian Denley wrote:
>> Nothing when that’s what you want.  But using ALC to control xcvr power is 
>> uncontrolled compression that may or may not be desired.
>> 
>> Brian
>> KB1VBF
>> Sent from my iPad
>> 
>>> On Jul 12, 2019, at 4:09 PM, Wes  wrote:
>>> 
>>> And what exactly is the problem with compression?  It's used all over the 
>>> place.
>>> 
>>> Wes  N7WS
>>> 
 On 6/28/2019 11:38 AM, Brian Denley wrote:
 I have always thought that ALC is not appropriate for power control.  It’s 
 a protection system.  Over use of ALC acts like compression.  No?
 
 Brian
 KB1VBF
 Sent from my iPad
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Re: [Elecraft] ALC implementation

[Wes]

You do know that the K3(S) uses a slow ALC system for power control don't you?

Wes  N7WS

On 7/12/2019 8:53 PM, Brian Denley wrote:

Nothing when that’s what you want.  But using ALC to control xcvr power is 
uncontrolled compression that may or may not be desired.

Brian
KB1VBF
Sent from my iPad


On Jul 12, 2019, at 4:09 PM, Wes  wrote:

And what exactly is the problem with compression?  It's used all over the place.

Wes  N7WS


On 6/28/2019 11:38 AM, Brian Denley wrote:
I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?

Brian
KB1VBF
Sent from my iPad

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Re: [Elecraft] ALC implementation

[Brian Denley]

Nothing when that’s what you want.  But using ALC to control xcvr power is 
uncontrolled compression that may or may not be desired.  

Brian
KB1VBF
Sent from my iPad

> On Jul 12, 2019, at 4:09 PM, Wes  wrote:
> 
> And what exactly is the problem with compression?  It's used all over the 
> place.
> 
> Wes  N7WS
> 
>> On 6/28/2019 11:38 AM, Brian Denley wrote:
>> I have always thought that ALC is not appropriate for power control.  It’s a 
>> protection system.  Over use of ALC acts like compression.  No?
>> 
>> Brian
>> KB1VBF
>> Sent from my iPad
> 
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Re: [Elecraft] ALC implementation

[Jim Brown]

A common cause of incidental AM is ripple in the crystal filter(s) in 
use. One reason I went to the 2.8 kHz filter was that it had less 
ripple, and the difference was obvious on RTTY.


73, Jim K9YC

On 7/12/2019 3:45 PM, Conrad PA5Y wrote:

It should be mentioned that FT8 and JT65 are constant envelope and therefore 
there should not be any AF envelope to follow. Actually when I recently 
measured the AF output from WSJT-X there was a tiny amount of AM, around 1.4% 
in fact which so small as to be of no consequence.



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Re: [Elecraft] ALC implementation

[Wes]

Actually, gain compression reduces "gain" not dynamic range.  All signals are 
reduced in amplitude by the same number of dB.  This is the only way it doesn't 
introduce distortion.


This reminds me of the endless discussions about RX AGC where everyone has their 
favorite combination of rf-gain, threshold, slope, etc, that somehow magically 
reduces strong signals while allowing weaker ones to "pop out of the noise."  If 
you have one of these receivers, you best only use it for FM reception.


There is nothing inherently wrong with using compression, i.e. ALC on digital 
modes if the time constants are appropriate.  I have just run some tests on my 
K3S on FT8 while looking at the spectrum on a spectrum analyzer and listening 
with a second K3 for the dreaded in-band harmonics while "overdriving" the audio 
into the ALC region. With the present setup, I got the "recommended" 4-5 bars 
with the Line In at about 7 to 8.  Cranking it up to 30 and maxing out the ALC 
at 8 bars made no difference in detectable in-band harmonics, even using a 300 
Hz offset. (Split was off)


It's funny that this guy, https://www.youtube.com/watch?v=smWp0TOEtlQ decides 
that speech processing has no undesired effects yet is adamant that ALC should 
not be used.


Wes  N7WS



On 7/12/2019 2:41 PM, Bob McGraw K4TAX wrote:

Don't confuse compression and clipping.   Compression reduces dynamic range 
while clipping sets a hard ceiling and does generate distortion.  Compression 
used correctly does not generate distortion.

73
Bob, K4TAX


Sent from my iPhone


On Jul 12, 2019, at 4:00 PM, Wes  wrote:

What distortion?


On 7/12/2019 1:15 PM, Jim Rhodes wrote:
Nothing when it is done correctly on a mode that can stand the distortion. I 
personally won't use it on digital modes as my rigs tend to turn it off by 
default.

Jim Rhodes
K0XU

On Fri, Jul 12, 2019, 15:10 Wes mailto:wes_n...@triconet.org>> wrote:

And what exactly is the problem with compression?  It's used all over the
place.

Wes  N7WS

On 6/28/2019 11:38 AM, Brian Denley wrote:
> I have always thought that ALC is not appropriate for power control.
It’s a protection system.  Over use of ALC acts like compression.  No?
>
> Brian
> KB1VBF
> Sent from my iPad

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Re: [Elecraft] ALC implementation

[Conrad PA5Y]

It should be mentioned that FT8 and JT65 are constant envelope and therefore 
there should not be any AF envelope to follow. Actually when I recently 
measured the AF output from WSJT-X there was a tiny amount of AM, around 1.4% 
in fact which so small as to be of no consequence.  ALC can introduce AM quite 
easily if not properly implemented or adjusted. The recommended method of 
adjusting the K3S AF drive for digital modes works very well but each radio is 
different. The recent Icoms (IC-7300, IC7610 and IC9700) 50% indication on the 
ALC meter does not cause any degradation or spreading even for MSK144 which has 
16.5% AM. Presumably there is a small delay introduced to prevent overshoots, a 
so called 'look ahead' algorithm.

Regards

Conrad PA5Y

-Original Message-
From: elecraft-boun...@mailman.qth.net  On 
Behalf Of Fred Jensen
Sent: 13 July 2019 00:33
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] ALC implementation

Well ... I think it depends on your definition of distortion.  One can argue 
that, if the RF envelope does not exactly equal the original AF envelope, the 
signal has been distorted and that is certainly the case when the dynamic range 
has been reduced with compression.  It doesn't increase the occupied bandwidth 
however [at least not by much]. Clipping mows down the peaks, leaving sharp 
"edges" or signal transitions which do increase the occupied bandwidth.

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/12/2019 2:41 PM, Bob McGraw K4TAX wrote:
> Don't confuse compression and clipping.   Compression reduces dynamic range 
> while clipping sets a hard ceiling and does generate distortion.  Compression 
> used correctly does not generate distortion.
>
> 73
> Bob, K4TAX
>
>
> Sent from my iPhone
>
>> On Jul 12, 2019, at 4:00 PM, Wes  wrote:
>>
>> What distortion?
>>
>>> On 7/12/2019 1:15 PM, Jim Rhodes wrote:
>>> Nothing when it is done correctly on a mode that can stand the distortion. 
>>> I personally won't use it on digital modes as my rigs tend to turn it off 
>>> by default.
>>>
>>> Jim Rhodes
>>> K0XU
>>>
>>> On Fri, Jul 12, 2019, 15:10 Wes >> <mailto:wes_n...@triconet.org>> wrote:
>>>
>>> And what exactly is the problem with compression?  It's used all over 
>>> the
>>> place.
>>>
>>> Wes  N7WS
>>>
>>> On 6/28/2019 11:38 AM, Brian Denley wrote:
>>> > I have always thought that ALC is not appropriate for power control.
>>> It’s a protection system.  Over use of ALC acts like compression.  No?
>>> >
>>> > Brian
>>> > KB1VBF
>>> > Sent from my iPad
>>>
>>>

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Re: [Elecraft] ALC implementation

[Fred Jensen]

Well ... I think it depends on your definition of distortion.  One can 
argue that, if the RF envelope does not exactly equal the original AF 
envelope, the signal has been distorted and that is certainly the case 
when the dynamic range has been reduced with compression.  It doesn't 
increase the occupied bandwidth however [at least not by much].  
Clipping mows down the peaks, leaving sharp "edges" or signal 
transitions which do increase the occupied bandwidth.


73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/12/2019 2:41 PM, Bob McGraw K4TAX wrote:

Don't confuse compression and clipping.   Compression reduces dynamic range 
while clipping sets a hard ceiling and does generate distortion.  Compression 
used correctly does not generate distortion.

73
Bob, K4TAX


Sent from my iPhone


On Jul 12, 2019, at 4:00 PM, Wes  wrote:

What distortion?


On 7/12/2019 1:15 PM, Jim Rhodes wrote:
Nothing when it is done correctly on a mode that can stand the distortion. I 
personally won't use it on digital modes as my rigs tend to turn it off by 
default.

Jim Rhodes
K0XU

On Fri, Jul 12, 2019, 15:10 Wes mailto:wes_n...@triconet.org>> wrote:

And what exactly is the problem with compression?  It's used all over the
place.

Wes  N7WS

On 6/28/2019 11:38 AM, Brian Denley wrote:
> I have always thought that ALC is not appropriate for power control.
It’s a protection system.  Over use of ALC acts like compression.  No?
>
> Brian
> KB1VBF
> Sent from my iPad




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Re: [Elecraft] ALC implementation

[Bob McGraw K4TAX]

Don't confuse compression and clipping.   Compression reduces dynamic range 
while clipping sets a hard ceiling and does generate distortion.  Compression 
used correctly does not generate distortion. 

73
Bob, K4TAX


Sent from my iPhone

> On Jul 12, 2019, at 4:00 PM, Wes  wrote:
> 
> What distortion?
> 
>> On 7/12/2019 1:15 PM, Jim Rhodes wrote:
>> Nothing when it is done correctly on a mode that can stand the distortion. I 
>> personally won't use it on digital modes as my rigs tend to turn it off by 
>> default.
>> 
>> Jim Rhodes
>> K0XU
>> 
>> On Fri, Jul 12, 2019, 15:10 Wes > > wrote:
>> 
>>And what exactly is the problem with compression?  It's used all over the
>>place.
>> 
>>Wes  N7WS
>> 
>>On 6/28/2019 11:38 AM, Brian Denley wrote:
>>> I have always thought that ALC is not appropriate for power control. 
>>It’s a protection system.  Over use of ALC acts like compression.  No?
>>>
>>> Brian
>>> KB1VBF
>>> Sent from my iPad
>> 
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Re: [Elecraft] ALC implementation

[Wes]

What distortion?

On 7/12/2019 1:15 PM, Jim Rhodes wrote:
Nothing when it is done correctly on a mode that can stand the distortion. I 
personally won't use it on digital modes as my rigs tend to turn it off by 
default.


Jim Rhodes
K0XU

On Fri, Jul 12, 2019, 15:10 Wes > wrote:


And what exactly is the problem with compression?  It's used all over the
place.

Wes  N7WS

On 6/28/2019 11:38 AM, Brian Denley wrote:
> I have always thought that ALC is not appropriate for power control. 
It’s a protection system.  Over use of ALC acts like compression.  No?
>
> Brian
> KB1VBF
> Sent from my iPad

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Re: [Elecraft] ALC implementation

[Jim Rhodes]

Nothing when it is done correctly on a mode that can stand the distortion.
I personally won't use it on digital modes as my rigs tend to turn it off
by default.

Jim Rhodes
K0XU

On Fri, Jul 12, 2019, 15:10 Wes  wrote:

> And what exactly is the problem with compression?  It's used all over the
> place.
>
> Wes  N7WS
>
> On 6/28/2019 11:38 AM, Brian Denley wrote:
> > I have always thought that ALC is not appropriate for power control.
> It’s a protection system.  Over use of ALC acts like compression.  No?
> >
> > Brian
> > KB1VBF
> > Sent from my iPad
>
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Re: [Elecraft] ALC implementation

[Wes]

And what exactly is the problem with compression?  It's used all over the place.

Wes  N7WS

On 6/28/2019 11:38 AM, Brian Denley wrote:

I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?

Brian
KB1VBF
Sent from my iPad


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Re: [Elecraft] ALC implementation

[Don Wilhelm]

Greg,

The Elecraft power control is done in the RF stages and not the audio.
After a band change or a change in the POWER knob, the power control 
loop is reset.
The response time is quick enough that you do not notice it in normal 
operation, although it does take a dot or two in CW or a couple of 
syllables in voice to obtain enough RF output to be properly measured by 
the wattmeter and fed back to the MCU.


In the case of digital modes, if the audio is not sufficient, the 
measured power will be lower than what is requested by the power knob 
and the radio will begin to ramp up power - but if one or more of the RF 
stages has reached its limit, there will not be enough power, and the RF 
output level will come up quite slowly or not at all - so the radio 
continually "hunts" for the power the power requested, but never makes it.


So keep the audio up to that specified for data (4 bars solid, 5th 
flashing) or voice modes (5 to 7 bars) and all will be well.


73,
Don W3FPR

On 6/29/2019 1:35 PM, Greg Troxel wrote:

I have always been a bit unclear on what the Elecraft ALC/power was
really doing.

You mention low power then then hunting, and the notion of a set power
level, measuring, and adjusting gain.  That makes me think that there is
an initial gain that is computed/calibrated somehow, that if right will
not result in an adjustment right away.  Presumably that's a known
relationship between an audio input of an appropriate power and the
desired RF level.  Is that a fair characterization, or if not, could you
explain how it's wrong?

I am guessing also that there is some kind of silence detection or max
gain, as keying the mic without speaking doesn't lead to ramping up to
full-power transmitted noise.  I could see the power loop having a
narrow range, enough to account for how much variance there should be,
but not 40 dB worth.

I have seen repeatedly about "4 bars solid and 5th flashing" as the
right place, and the "no ALC" point.  Is there really an ALC circuit,
that reduces gain in the audio stage when a higher input level is
measured?  Does this have a sufficiently long decay time constant so
that an FT8 or PSK signal would get adjusted acceptably and still have a
low-distortion signal?  Or is there still a transfer slope where the
output ends up too high?

Overall, this seems like having two coupled control loops instead of
one, and I'm guessing that the point is to have different time constants
in each one, or to get the levels right at two points in the circuit
instead of one, by having audio gain and RF gain separately controlled.
Is that accurate?

Separately, I wonder about issues with different levels of different
audio frequencies resulting in a transmitted signal which while not
necessarily distorted is off plan and therefore less well decoded
(assuming there isn't adaptive equalization in the decoder after pilot
tones, and I don't have the impression there is).  Does this end up
being an issue in practice?  I would hope that with the relatively close
spacing within an FT8 signal that this is likely to be not a problem.

tnx es 73 de n1dam



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Re: [Elecraft] ALC implementation

[Greg Troxel]

Don Wilhelm  writes:

> The above method works fine for many transceivers, but NOT for
> Elecraft which measures the actual power output, compares it with the
> set power and adjusts the RF drive accordingly.  This is a fully
> closed loop system.  As far as I know, Elecraft is the only amateur
> transceiver using that type of system.
>
> With Elecraft transceivers (except for the K2), adjust the audio drive
> level to produce 4 bars solid on the ALC meter with the 5th bar
> flashing (this is the NO ALC point.  Then leave it that way and adjust
> the desired power with the power knob.  Doing otherwise will result in
> low power at the start and power hunting as the transmission goes on.

I have always been a bit unclear on what the Elecraft ALC/power was
really doing.

You mention low power then then hunting, and the notion of a set power
level, measuring, and adjusting gain.  That makes me think that there is
an initial gain that is computed/calibrated somehow, that if right will
not result in an adjustment right away.  Presumably that's a known
relationship between an audio input of an appropriate power and the
desired RF level.  Is that a fair characterization, or if not, could you
explain how it's wrong?

I am guessing also that there is some kind of silence detection or max
gain, as keying the mic without speaking doesn't lead to ramping up to
full-power transmitted noise.  I could see the power loop having a
narrow range, enough to account for how much variance there should be,
but not 40 dB worth.

I have seen repeatedly about "4 bars solid and 5th flashing" as the
right place, and the "no ALC" point.  Is there really an ALC circuit,
that reduces gain in the audio stage when a higher input level is
measured?  Does this have a sufficiently long decay time constant so
that an FT8 or PSK signal would get adjusted acceptably and still have a
low-distortion signal?  Or is there still a transfer slope where the
output ends up too high?

Overall, this seems like having two coupled control loops instead of
one, and I'm guessing that the point is to have different time constants
in each one, or to get the levels right at two points in the circuit
instead of one, by having audio gain and RF gain separately controlled.
Is that accurate?

Separately, I wonder about issues with different levels of different
audio frequencies resulting in a transmitted signal which while not
necessarily distorted is off plan and therefore less well decoded
(assuming there isn't adaptive equalization in the decoder after pilot
tones, and I don't have the impression there is).  Does this end up
being an issue in practice?  I would hope that with the relatively close
spacing within an FT8 signal that this is likely to be not a problem.

tnx es 73 de n1dam
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Re: [Elecraft] ALC implementation

[Jim Brown]

Right.  Almost ten years ago, I used an audio FFT to measure the 
harmonics in a Thinkpad's line level (also used for headphones) output. 
The distortion decreased by 10 dB when the output was first set just 
below clip and then reduced by 6 dB (half the output voltage).  Just 
below clip, the second harmonic was -30 dB; at half that voltage out, it 
was -40 dB. To put this in perspective, Thinkpads are better than 
average laptops.


This is the basis of advice I first published around that time to first 
set the output level of sound cards 6-10 dB below full output and then 
set input level in the rig. There are app notes on my website that 
describe three different ways to do this, depending on your available 
tools, one being our ears!


The "ears" method is this.  Plug headphones into the computer output 
jack, have the computer generate the tone(s) your going to transmit, and 
increase the output level until you hear the tone(s) sound a bit 
rougher, then back off the output of the computer until the tone(s) 
sound half as loud. This works because our ear/brain perceives a change 
in loudness of 6-10 dB as "half (or twice) as loud."


73, Jim K9YC

On 6/28/2019 2:29 PM, Joe Subich, W4TV wrote:


Among other issues, this article is incorrect when calling for the
"Device" (Master) volume level in Windows to be set to 100%. Nearly
every sound card for which I've seen test results has increased
distortion above the 70 - 80% level (-1 to -2 dB or -3 to -6 dB
depending on the driver calibration) and some "inexpensive" devices
have significant distortion above 50% (-3 or -10 dB depending on
driver calibration).

One will have a cleaner signal, all other things being the same, by
setting the Windows "Device" (Master) slider down a bit and increasing
the transceiver mic gain (Line In, DATA In, etc.) slightly.  In most
cases, with the sound card "Master" at 70 - 80%, the transceiver mic
gain will still be relatively low.

73,

   ... Joe, W4TV


On 2019-06-28 10:18 AM, Andy Durbin wrote:
Does anyone know of any rig that uses "compression" rather than 
linear gain control to implement ALC?


ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1

73,
Andy, k3wyc


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Re: [Elecraft] ALC implementation

[Joe Subich, W4TV]

Among other issues, this article is incorrect when calling for the
"Device" (Master) volume level in Windows to be set to 100%.  Nearly
every sound card for which I've seen test results has increased
distortion above the 70 - 80% level (-1 to -2 dB or -3 to -6 dB
depending on the driver calibration) and some "inexpensive" devices
have significant distortion above 50% (-3 or -10 dB depending on
driver calibration).

One will have a cleaner signal, all other things being the same, by
setting the Windows "Device" (Master) slider down a bit and increasing
the transceiver mic gain (Line In, DATA In, etc.) slightly.  In most
cases, with the sound card "Master" at 70 - 80%, the transceiver mic
gain will still be relatively low.

73,

   ... Joe, W4TV


On 2019-06-28 10:18 AM, Andy Durbin wrote:

Does anyone know of any rig that uses "compression" rather than linear gain 
control to implement ALC?

ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1

73,
Andy, k3wyc


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Re: [Elecraft] ALC implementation

[Wes]

Analog ALC is a fully closed loop too. And Elecraft measuring the output and 
generating feedback isn't without flaw either. There is an ADC in that output 
measurement system that introduces low-level power jitter easily observed on a 
spectrum analyzer.


Wes  N7WS


On 6/28/2019 12:04 PM, Don Wilhelm wrote:

Brian,

ALC should never be used for power control doing so usually causes RF 
compression and distortion.


Many of the digital application instructions tell you to set for NO ALC as a 
*maximum* audio level, set the power control for the maximum desired and then 
reduce the audio level to reduce the power - I think that is why the slider in 
WSJTX is labeled POWER when it is really an audio level control.


The above method works fine for many transceivers, but NOT for Elecraft which 
measures the actual power output, compares it with the set power and adjusts 
the RF drive accordingly.  This is a fully closed loop system.  As far as I 
know, Elecraft is the only amateur transceiver using that type of system.


With Elecraft transceivers (except for the K2), adjust the audio drive level 
to produce 4 bars solid on the ALC meter with the 5th bar flashing (this is 
the NO ALC point.  Then leave it that way and adjust the desired power with 
the power knob.  Doing otherwise will result in low power at the start and 
power hunting as the transmission goes on.


73,
Don W3FPR

On 6/28/2019 2:38 PM, Brian Denley wrote:
I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?



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Re: [Elecraft] ALC implementation

[Don Wilhelm]

Richard,

When you put the KX3 into DATA A mode, the mic gain is reduced to 
something resembling Line level.


Depending on your soundcard output, you may still need an attenuator.
Strive for each audio control in the computer and application to be at 
30 to 50%, and then if you have too much audio with the KX3 MIC Gain set 
near its mid-point, then you will have to add an attenuator.


One note on the KX3 - if you drive the audio with too large a signal, 
the mic amplifier will shut down and the MIC GAIN will not work anywhere 
in its range.


73,
Don W3FPR

On 6/28/2019 3:01 PM, Richard Corfield wrote:

That's interesting thanks. It means that by aiming for no ALC indication
I've been under modulating.

I assume the input stage in the KX3 can take higher levels?

On Fri, 28 Jun 2019, 16:35 Bob McGraw K4TAX,  wrote:


Well written generic paper for operation of FT-8 and other digital
signals of like mode.   It does not totally nor correctly apply to
Elecraft radios as power management is handled by a totally different
means.   And those means and methods suggested in this paper are not
applicable to Elecraft radios for power control.   From experience in
set-up and operating different radios and different interfaces, I do
believe that the WSJT-X operating panel which shows the right slider
labeled PWR is very misleading and should be changed to some other
description i.e. TX AUD.

While many radios use the control of audio level to adjust power output,
this is somewhat misleading as there are control areas available such as
SPKR level in Windows, and Line Gain for the radios or perhaps an
external sound card device.   Again, the use of the acronym MIC is
always a frighting term,  in as much as many systems produce a transmit
audio level that will overdrive the microphone pre-amplifier input.
Once this occurs, reducing MIC gain will not relieve the distorted audio
as it occurs pre level control in the circuit.   Frankly, one should not
connect the sound card to a microphone input without proper and correct
means of attenuating the signal before it is connected to the microphone
input.   In addition, this will always preserve the transmit
Signal-to-Noise ratio.

As to "compression" I take that to mean Speech Processing, which should
ALWAYS be off or set to a zero value.   Likewise for EQ, again always
set to OFF or FLAT  for transmit and receive purposes as well.

As a mater of practice, there are three or perhaps four distinct places
that audio levels can be controlled in the transmit path. First is SPKR
level which is the audio level out of the computer. Second is the WSJT-X
PWR slider, and third is the Line Gain within the radio.  A fourth, if
used, would be an external interface such as a Signalink or
Soundblaster.   If any of these points end up near minimum value or near
maximum value, I strongly suggest further investigation as to why and
remedial steps taken to more "normalize" the control values at all
points in the system.

Some radios do have "meter" indicators which relate to ALC levels while
others simply prove a visual means usually the illumination of a LED.
In all cases, the indicators should be observed, and the radio operated
accordingly with NO indicated ALC action occurring.Again, regarding
Elecraft radios, the first 4 bars on the "ALC Scale" are audio level and
NOT ALC action.  The onset of actual ALC occurs at the 5th bar and higher.

73

Bob, K4TAX




On 6/28/2019 9:18 AM, Andy Durbin wrote:

Does anyone know of any rig that uses "compression" rather than linear

gain control to implement ALC?


ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1

73,
Andy, k3wyc
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Post: 

Re: [Elecraft] ALC implementation

[Wes]

Depends on the time constants.

Wes  N7WS

On 6/28/2019 11:51 AM, Dr. William J. Schmidt wrote:

It's very nature causes the resulting overall transfer function to become 
non-linear, leading to distortion and other unwanted by products when active.



-Original Message-
From: elecraft-boun...@mailman.qth.net 
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Brian Denley
Sent: Friday, June 28, 2019 1:38 PM
To: Jim Rhodes 
Cc: elecraft@mailman.qth.net; Andy Durbin 
Subject: Re: [Elecraft] ALC implementation

I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?

Brian
KB1VBF
Sent from my iPad


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Re: [Elecraft] ALC implementation

[Andy Durbin]

" which measures the actual power output, compares it with the set power
and adjusts the RF drive accordingly.  This is a fully closed loop
system.  As far as I know, Elecraft is the only amateur transceiver
using that type of system."

I think you will find that is exactly how TS-590 power control works.

73,
Andy, k3wyc




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Re: [Elecraft] ALC implementation

[Don Wilhelm]

Brian,

ALC should never be used for power control doing so usually causes RF 
compression and distortion.


Many of the digital application instructions tell you to set for NO ALC 
as a *maximum* audio level, set the power control for the maximum 
desired and then reduce the audio level to reduce the power - I think 
that is why the slider in WSJTX is labeled POWER when it is really an 
audio level control.


The above method works fine for many transceivers, but NOT for Elecraft 
which measures the actual power output, compares it with the set power 
and adjusts the RF drive accordingly.  This is a fully closed loop 
system.  As far as I know, Elecraft is the only amateur transceiver 
using that type of system.


With Elecraft transceivers (except for the K2), adjust the audio drive 
level to produce 4 bars solid on the ALC meter with the 5th bar flashing 
(this is the NO ALC point.  Then leave it that way and adjust the 
desired power with the power knob.  Doing otherwise will result in low 
power at the start and power hunting as the transmission goes on.


73,
Don W3FPR

On 6/28/2019 2:38 PM, Brian Denley wrote:

I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?


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Re: [Elecraft] ALC implementation

[Richard Corfield]

That's interesting thanks. It means that by aiming for no ALC indication
I've been under modulating.

I assume the input stage in the KX3 can take higher levels?

On Fri, 28 Jun 2019, 16:35 Bob McGraw K4TAX,  wrote:

> Well written generic paper for operation of FT-8 and other digital
> signals of like mode.   It does not totally nor correctly apply to
> Elecraft radios as power management is handled by a totally different
> means.   And those means and methods suggested in this paper are not
> applicable to Elecraft radios for power control.   From experience in
> set-up and operating different radios and different interfaces, I do
> believe that the WSJT-X operating panel which shows the right slider
> labeled PWR is very misleading and should be changed to some other
> description i.e. TX AUD.
>
> While many radios use the control of audio level to adjust power output,
> this is somewhat misleading as there are control areas available such as
> SPKR level in Windows, and Line Gain for the radios or perhaps an
> external sound card device.   Again, the use of the acronym MIC is
> always a frighting term,  in as much as many systems produce a transmit
> audio level that will overdrive the microphone pre-amplifier input.
> Once this occurs, reducing MIC gain will not relieve the distorted audio
> as it occurs pre level control in the circuit.   Frankly, one should not
> connect the sound card to a microphone input without proper and correct
> means of attenuating the signal before it is connected to the microphone
> input.   In addition, this will always preserve the transmit
> Signal-to-Noise ratio.
>
> As to "compression" I take that to mean Speech Processing, which should
> ALWAYS be off or set to a zero value.   Likewise for EQ, again always
> set to OFF or FLAT  for transmit and receive purposes as well.
>
> As a mater of practice, there are three or perhaps four distinct places
> that audio levels can be controlled in the transmit path. First is SPKR
> level which is the audio level out of the computer. Second is the WSJT-X
> PWR slider, and third is the Line Gain within the radio.  A fourth, if
> used, would be an external interface such as a Signalink or
> Soundblaster.   If any of these points end up near minimum value or near
> maximum value, I strongly suggest further investigation as to why and
> remedial steps taken to more "normalize" the control values at all
> points in the system.
>
> Some radios do have "meter" indicators which relate to ALC levels while
> others simply prove a visual means usually the illumination of a LED.
> In all cases, the indicators should be observed, and the radio operated
> accordingly with NO indicated ALC action occurring.Again, regarding
> Elecraft radios, the first 4 bars on the "ALC Scale" are audio level and
> NOT ALC action.  The onset of actual ALC occurs at the 5th bar and higher.
>
> 73
>
> Bob, K4TAX
>
>
>
>
> On 6/28/2019 9:18 AM, Andy Durbin wrote:
> > Does anyone know of any rig that uses "compression" rather than linear
> gain control to implement ALC?
> >
> > ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1
> >
> > 73,
> > Andy, k3wyc
> > __
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> > Message delivered to rmcg...@blomand.net
> >
>
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Re: [Elecraft] ALC implementation

[Dr. William J. Schmidt]

It's very nature causes the resulting overall transfer function to become 
non-linear, leading to distortion and other unwanted by products when active.



-Original Message-
From: elecraft-boun...@mailman.qth.net 
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Brian Denley
Sent: Friday, June 28, 2019 1:38 PM
To: Jim Rhodes 
Cc: elecraft@mailman.qth.net; Andy Durbin 
Subject: Re: [Elecraft] ALC implementation

I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?

Brian
KB1VBF
Sent from my iPad

> On Jun 28, 2019, at 1:11 PM, Jim Rhodes  wrote:
> 
> Yes Andy, I used a TS590 at field day. But this is the Elecraft reflector.
> These rigs work differently. Use my K3 for FT8 often. I built an 
> interface for my Kenwood rig too. But you treat them differently.
> 
> Jim Rhodes
> K0XU
> 
>> On Fri, Jun 28, 2019, 11:21 Andy Durbin  wrote:
>> 
>> I strongly disagree that ALC should be zero for FT8 but that is based 
>> only on my experience with the TS-590S.
>> 
>> My draft paper on FT8 harmonics can be found here -
>> 
>> 
>> https://www.dropbox.com/s/85aoc937kz235iq/FT8%20audio%20harmonics%20d
>> raft%20d%20k3wyc.pdf?dl=0
>> 
>> ALC must be in the control range for closed loop power control to 
>> work on a TS-590. Operating in the normal ALC range with a TS-590 
>> does not degrade the F8 signal.
>> 
>> 73,
>> Andy k3wyc
>> 
>> 
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Re: [Elecraft] ALC implementation

[Jim Brown]

On 6/28/2019 11:38 AM, Brian Denley wrote:

I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.


You are absolutely right. ALC should never be used between a transceiver 
and an amplifier for power control. Likewise, for digital modes, audio 
drive level should never be used to set output power, but rather so that 
levels are within the best operating range of both computer and radio 
audio stages.


73, Jim K9YC

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Re: [Elecraft] ALC implementation

[Brian Denley]

I have always thought that ALC is not appropriate for power control.  It’s a 
protection system.  Over use of ALC acts like compression.  No?

Brian
KB1VBF
Sent from my iPad

> On Jun 28, 2019, at 1:11 PM, Jim Rhodes  wrote:
> 
> Yes Andy, I used a TS590 at field day. But this is the Elecraft reflector.
> These rigs work differently. Use my K3 for FT8 often. I built an interface
> for my Kenwood rig too. But you treat them differently.
> 
> Jim Rhodes
> K0XU
> 
>> On Fri, Jun 28, 2019, 11:21 Andy Durbin  wrote:
>> 
>> I strongly disagree that ALC should be zero for FT8 but that is based only
>> on my experience with the TS-590S.
>> 
>> My draft paper on FT8 harmonics can be found here -
>> 
>> 
>> https://www.dropbox.com/s/85aoc937kz235iq/FT8%20audio%20harmonics%20draft%20d%20k3wyc.pdf?dl=0
>> 
>> ALC must be in the control range for closed loop power control to work on
>> a TS-590. Operating in the normal ALC range with a TS-590 does not degrade
>> the F8 signal.
>> 
>> 73,
>> Andy k3wyc
>> 
>> 
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Re: [Elecraft] ALC implementation

[Jim Rhodes]

Yes Andy, I used a TS590 at field day. But this is the Elecraft reflector.
These rigs work differently. Use my K3 for FT8 often. I built an interface
for my Kenwood rig too. But you treat them differently.

Jim Rhodes
K0XU

On Fri, Jun 28, 2019, 11:21 Andy Durbin  wrote:

> I strongly disagree that ALC should be zero for FT8 but that is based only
> on my experience with the TS-590S.
>
> My draft paper on FT8 harmonics can be found here -
>
>
> https://www.dropbox.com/s/85aoc937kz235iq/FT8%20audio%20harmonics%20draft%20d%20k3wyc.pdf?dl=0
>
> ALC must be in the control range for closed loop power control to work on
> a TS-590. Operating in the normal ALC range with a TS-590 does not degrade
> the F8 signal.
>
> 73,
> Andy k3wyc
>
>
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Re: [Elecraft] ALC implementation

[Andy Durbin]

I strongly disagree that ALC should be zero for FT8 but that is based only on 
my experience with the TS-590S.

My draft paper on FT8 harmonics can be found here -

https://www.dropbox.com/s/85aoc937kz235iq/FT8%20audio%20harmonics%20draft%20d%20k3wyc.pdf?dl=0

ALC must be in the control range for closed loop power control to work on a 
TS-590. Operating in the normal ALC range with a TS-590 does not degrade the F8 
signal.

73,
Andy k3wyc


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Re: [Elecraft] ALC implementation

[Bob McGraw K4TAX]

Well written generic paper for operation of FT-8 and other digital 
signals of like mode.   It does not totally nor correctly apply to 
Elecraft radios as power management is handled by a totally different 
means.   And those means and methods suggested in this paper are not 
applicable to Elecraft radios for power control.   From experience in 
set-up and operating different radios and different interfaces, I do 
believe that the WSJT-X operating panel which shows the right slider 
labeled PWR is very misleading and should be changed to some other 
description i.e. TX AUD.


While many radios use the control of audio level to adjust power output, 
this is somewhat misleading as there are control areas available such as 
SPKR level in Windows, and Line Gain for the radios or perhaps an 
external sound card device.   Again, the use of the acronym MIC is 
always a frighting term,  in as much as many systems produce a transmit 
audio level that will overdrive the microphone pre-amplifier input.  
Once this occurs, reducing MIC gain will not relieve the distorted audio 
as it occurs pre level control in the circuit.   Frankly, one should not 
connect the sound card to a microphone input without proper and correct 
means of attenuating the signal before it is connected to the microphone 
input.   In addition, this will always preserve the transmit 
Signal-to-Noise ratio.


As to "compression" I take that to mean Speech Processing, which should 
ALWAYS be off or set to a zero value.   Likewise for EQ, again always 
set to OFF or FLAT  for transmit and receive purposes as well.


As a mater of practice, there are three or perhaps four distinct places 
that audio levels can be controlled in the transmit path. First is SPKR 
level which is the audio level out of the computer. Second is the WSJT-X 
PWR slider, and third is the Line Gain within the radio.  A fourth, if 
used, would be an external interface such as a Signalink or 
Soundblaster.   If any of these points end up near minimum value or near 
maximum value, I strongly suggest further investigation as to why and 
remedial steps taken to more "normalize" the control values at all 
points in the system.


Some radios do have "meter" indicators which relate to ALC levels while 
others simply prove a visual means usually the illumination of a LED.  
In all cases, the indicators should be observed, and the radio operated 
accordingly with NO indicated ALC action occurring.    Again, regarding 
Elecraft radios, the first 4 bars on the "ALC Scale" are audio level and 
NOT ALC action.  The onset of actual ALC occurs at the 5th bar and higher.


73

Bob, K4TAX




On 6/28/2019 9:18 AM, Andy Durbin wrote:

Does anyone know of any rig that uses "compression" rather than linear gain 
control to implement ALC?

ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1

73,
Andy, k3wyc
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[Elecraft] ALC implementation

[Andy Durbin]

Does anyone know of any rig that uses "compression" rather than linear gain 
control to implement ALC?

ref - https://www.dropbox.com/s/f4uaop5tqwzaweu/FT8Noise6.docx?dl=1

73,
Andy, k3wyc
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