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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:
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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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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, < [hidden email]> 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
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft> > Help: http://mailman.qth.net/mmfaq.htm> > Post: mailto: [hidden email]
> >
> > This list hosted by: http://www.qsl.net> > Please help support this email list: http://www.qsl.net/donate.html> > Message delivered to [hidden email]
> >
>
> ______________________________________________________________
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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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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, < [hidden email]> 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
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft>>> Help: http://mailman.qth.net/mmfaq.htm>>> Post: mailto: [hidden email]
>>>
>>> This list hosted by: http://www.qsl.net>>> Please help support this email list: http://www.qsl.net/donate.html>>> Message delivered to [hidden email]
>>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft>> Help: http://mailman.qth.net/mmfaq.htm>> Post: mailto: [hidden email]
>>
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>
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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?
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft> Help: http://mailman.qth.net/mmfaq.htm> Post: mailto: [hidden email]
>
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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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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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>
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Don Wilhelm < [hidden email]> 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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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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