[K3] Power too high in PSK31 / SSB

[Julian, G4ILO]

I have just noticed that my K3 appears to be giving vastly more peak power out than the value selected by the power control. I assume that this issue has occurred since my loading the version 2.38 production firmware after returning from holiday, because I did not have this problem before then.

The constant carrier power level when TUNE is pressed appears to be correct. However in PSK31 mode I am getting almost full scale on the internal meter when 40W is dialled up. When the PSK software sends a tune signal (pure tone) an external power meter shows about twice the amount of power that has been specified. On SSB at 100W the internal meter seems to be at full scale most of the time as well.

Has anyone else experienced this, and what is the solution?

[Rob May-2]

I worked some PSK today at 20 watts and it seems to be fine.  Just a couple of bars on the RF meter when I have the power dialed to 20 watts.  I running the latest beta (2.45) but I didn't have any problem with 2.38.  No compression, mic gain turned down so that the ALC just barely makes one bar.
Rob
NV5E
K3 #1417

> Date: Fri, 3 Oct 2008 15:35:16 -0700
> From: [hidden email]
> To: [hidden email]
> Subject: [Elecraft] [K3] Power too high in PSK31 / SSB
>
>
> I have just noticed that my K3 appears to be giving vastly more peak power
> out than the value selected by the power control. I assume that this issue
> has occurred since my loading the version 2.38 production firmware after
> returning from holiday, because I did not have this problem before then.
>
> The constant carrier power level when TUNE is pressed appears to be correct.
> However in PSK31 mode I am getting almost full scale on the internal meter
> when 40W is dialled up. When the PSK software sends a tune signal (pure
> tone) an external power meter shows about twice the amount of power that has
> been specified. On SSB at 100W the internal meter seems to be at full scale
> most of the time as well.
>
> Has anyone else experienced this, and what is the solution?
>
> -----
> Julian, G4ILO. K2 #392 K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack http://www.ham-directory.com/ Ham
> Directory http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 and K3
> --
> View this message in context: http://n2.nabble.com/-K3--Power-too-high-in-PSK31---SSB-tp1143050p1143050.html
> Sent from the Elecraft mailing list archive at Nabble.com.
>
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[Julian, G4ILO]

Rob May-2 wrote

I worked some PSK today at 20 watts and it seems to be fine.  Just a couple of bars on the RF meter when I have the power dialed to 20 watts.  I running the latest beta (2.45) but I didn't have any problem with 2.38.  No compression, mic gain turned down so that the ALC just barely makes one bar.

In reply to someone who responded off-list, I am aware that the power when a pure tone is sent will be about twice the power shown when the transmitter is modulated. However, what I am seeing is the power not being limited to what the power control has set. For example, set 5W, key down in CW mode, 5W is transmitted. Switch to data mode, send a pure tone, 12W is transmitted. Something is wrong with the way the power control is working.

In reply to Rob, if I reduce the audio input level so that no ALC bars are shown, I can get the output power on a pure tone to follow what is set on the power control. However, this is not how we have been told the K3 should be set up, and it was not necessary to do this with previous versions of the firmware. Lyle stated in a post some months ago, that the ALC meter in data mode does not actually measure ALC, but signal level, and should be adjusted to a steady 4 or 5 bars to ensure adequate drive.

I will try the most recent release of the firmware to see if it makes a difference.

[Julian, G4ILO]

I *think* I have found the solution to the problem of my K3 giving more power than is set on the power control.

A few weeks ago, I recall someone on this reflector posting a paragraph from the manual on the lines that "the K3 will perform a gain calibration if TUNE is performed with the power set to .1W, 5W or 50W." I can't find the original posting now, but I recall someone commenting that they hoped that was not the case, and that it really only did this when the CONFIG menu was in operation.

Prior to the problem with the power levels occurring, I pressed the ATU button instead of the TUNE button when trying to tune my magnetic loop. I have TUN PWR set to 5W. The ATU tried to tune the grossly mismatched magnetic loop. After that, I pressed the TUNE button and tuned the loop for a match, and then pressed ATU TUNE again to tune the ATU back to what was presumably a 50 ohm load. It was at that point that I first noticed something didn't look quite right with the power levels.

I set TUN PWR to 3W to see whether the K3 was obeying the power levels. It did on CW but was still giving more than double that power when a sine wave was injected into the audio.

This morning I connected my power meter and did some more tests to confirm the problem I descrived last night. When I set TUN PWR to 5W and did a TUNE I noticed the power reading on the front panel display calibrating itself to 5W. After that I switched to DATA and injected a sine wave again and this time I got exactly the same power output - 5W.

I might be interpreting this wrongly but it seems to me that the concern raised in the original post is justified, and that if a tuning power of .1W, 5W or 50W is used, the K3 will calibrate its power control whether you want it to or not. If this happens when a badly mismatched load is connected or perhaps when the ATU is in circuit and mis-tuned then the calibration will be completely wrong, with the results that I experienced. I think that the K3 power calibration should not occur unless you have specifically selected an option that requests it.

By the way, if anyone wonders why I had the KAT3 active when using an external tuner as for the magnetic loop, the reason is simply that one of my antennas needs the KAT3 and one doesn't, and the K3 provides no way to link the KAT3 in/out with the selection of ANT 1/2.

[Joe Subich, W4TV-3]

> I am seeing is the power not being limited to what the power
> control has set. For example, set 5W, key down in CW mode, 5W
> is transmitted. Switch to data mode, send a pure tone, 12W is
> transmitted. Something is wrong with the way the power
> control is working.

Have you set a value for CONFIG:TXG VCE because you voice peaks
were not coming up to the CW level?  Adding a dB or two there
will cause PSK peak powers to run higher than the CW value.
 
> In reply to Rob, if I reduce the audio input level so that no
> ALC bars are shown, I can get the output power on a pure tone
> to follow what is set on the power control.

Running "no bars" of ALC in PSK/AFSK causes the microphone gain
to be increased to compensate for the insufficient drive.  This
will result in added distortion (noise and IMD).  

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Julian, G4ILO
> Sent: Saturday, October 04, 2008 5:47 AM
> To: [hidden email]
> Subject: RE: [Elecraft] Power too high in PSK31 / SSB
>
>
>
>
>
> Rob May-2 wrote:
> >
> > I worked some PSK today at 20 watts and it seems to be
> fine.  Just a
> > couple of bars on the RF meter when I have the power dialed to 20
> > watts. I running the latest beta (2.45) but I didn't have
> any problem
> > with 2.38. No compression, mic gain turned down so that the
> ALC just
> > barely makes one bar.
> >
> In reply to someone who responded off-list, I am aware that
> the power when a pure tone is sent will be about twice the
> power shown when the transmitter is modulated. However, what
> I am seeing is the power not being limited to what the power
> control has set. For example, set 5W, key down in CW mode, 5W
> is transmitted. Switch to data mode, send a pure tone, 12W is
> transmitted. Something is wrong with the way the power
> control is working.
>
> In reply to Rob, if I reduce the audio input level so that no
> ALC bars are shown, I can get the output power on a pure tone
> to follow what is set on the power control. However, this is
> not how we have been told the K3 should be set up, and it was
> not necessary to do this with previous versions of the
> firmware. Lyle stated in a post some months ago, that the ALC
> meter in data mode does not actually measure ALC, but signal
> level, and should be adjusted to a steady 4 or 5 bars to
> ensure adequate drive.
>
> I will try the most recent release of the firmware to see if
> it makes a difference.
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack  
> http://www.ham-directory.com/ Ham
> Directory    http://www.g4ilo.com/kcomm.html KComm for
> Elecraft K2 and K3
> --
> View this message in context:
> http://n2.nabble.com/-K3--Power-too-high-in-PSK31---SSB-tp1143

050p1143674.html
Sent from the Elecraft mailing list archive at Nabble.com.

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[Julian, G4ILO]

Joe Subich, W4TV-3 wrote

Have you set a value for CONFIG:TXG VCE because you voice peaks
were not coming up to the CW level?  Adding a dB or two there
will cause PSK peak powers to run higher than the CW value.
 

Good call. Than you. Yes, there was 2.0dB set in there. I'm not sure how it got there, because I don't have any peak reading meter so I would not have been able to tell if the voice peaks were lacking anyway. In fact, the power out on a pure tone is about 10% higher than on key down, even with TXG VCE re-set to 0.0db.

What I don't understand is how I appeared to fix the problem by running the TX gain calibration on each band into a dummy load again.

I would have assumed that if you set a particular power level, you would get no more than that amount of peak power out, regardless of any other setting. No wonder folks driving linears are complaining that they can't accurately set the output so they can't overdrive them. It seems to me that how much power the K3 puts out depends on what mood it's in. :)

[Rob May-2]

Joe, W4TV, wrote:


 Running "no bars" of ALC in PSK/AFSK causes the microphone gain
 to be increased to compensate for the insufficient drive. This
 will result in added distortion (noise and IMD)."



Richard, VE3JAY, wrote:


FWIW, I leave my K3's power control set at 100 watts, but I adjust the
mic gain control to a setting which ensures I get zero ALC reading
(even one bar causes a noticeable increase in IMD as measured on a
PSKmeter)."



So, no bars equals more noise and IMD or even one bar causes more IMD?  
These two statements seem to contradict each other.  I'm thinking that the
ALC will only limit mic gain, it won't bring it up if it's low, other wise you wouldn't
have any dynamic range on your voice, the ALC would tend to make everything
the same level.  I'll just keep doing the way I've been doing it.  I get good
reports and the power output that I expect.
Rob
NV5E



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[Joe Subich, W4TV-3]

> So, no bars equals more noise and IMD or even one bar causes
> more IMD?

My information comes directly from Lyle - I don't remember if
it was on the reflector or in a direct e-mail during testing
of some beta ALC code.

> FWIW, I leave my K3's power control set at 100 watts, but I
> adjust the mic gain control to a setting which ensures I get
> zero ALC reading (even one bar causes a noticeable increase
> in IMD as measured on a PSKmeter)."

Setting the power out to 100 watts in PSK will guarantee that
the final is being driven into compression on peaks if you see
ALC (enough drive to reach 100 watts).  

I measure no difference in IMD with no ALC (just below the
point at which the first bar shows) vs. five solid bars if
the power level is kept below about 60 watts.  Put another
way, if the peak (CW equivalent) power level is kept below
about 60 watts to prevent compression (and the onset of IMD
generation) in the K3's finals, there is no difference with
ALC just below the level of the first bar and five solid bars.
If the mic/line gain is open just enough to get power output
the PSK has more noise, has about 1 dB more IMD, and power
output is less stable than with five bars of ALC.  
 
What Rich's procedure does accomplish is assure that the power
output does not exceed the 50/60 watt level.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Rob May
> Sent: Saturday, October 04, 2008 11:03 AM
> To: [hidden email]
> Subject: RE: [Elecraft] Power too high in PSK31 / SSB
>
>
>
> Joe, W4TV, wrote:
>
>
>  Running "no bars" of ALC in PSK/AFSK causes the microphone
> gain  to be increased to compensate for the insufficient
> drive. This  will result in added distortion (noise and IMD)."
>
>
>
> Richard, VE3JAY, wrote:
>
>
> FWIW, I leave my K3's power control set at 100 watts, but I
> adjust the mic gain control to a setting which ensures I get
> zero ALC reading (even one bar causes a noticeable increase
> in IMD as measured on a PSKmeter)."
>
>
>
> So, no bars equals more noise and IMD or even one bar causes
> more IMD?  
> These two statements seem to contradict each other.  I'm
> thinking that the
> ALC will only limit mic gain, it won't bring it up if it's
> low, other wise you wouldn't
> have any dynamic range on your voice, the ALC would tend to
> make everything the same level.  I'll just keep doing the way
> I've been doing it.  I get good
> reports and the power output that I expect.
> Rob
> NV5E
>
>
>
> _________________________________________________________________
> See how Windows connects the people, information, and fun
> that are part of your life.
> http://clk.atdmt.com/MRT/go/msnnkwxp1020093175mrt/direct/01/__

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[Rob May-2]

Ok, Joe, that's the way I understand it and is the way I'm doing it.  I adjust mic gain with Digipan in "tune" mode until it's right at the level where the first bar starts to flash.    Compression is set at 0.  Output power is set with the Pwr knob.  I generally run between 5 and 20 watts on PSK.  I get good reports and make plenty of contacts, so I must be doing something right.  
Rob
NV5E

> From: [hidden email]
> To: [hidden email]; [hidden email]
> Subject: RE: [Elecraft] Power too high in PSK31 / SSB
> Date: Sat, 4 Oct 2008 12:18:46 -0400
>
>
>
>> So, no bars equals more noise and IMD or even one bar causes
>> more IMD?
>
> My information comes directly from Lyle - I don't remember if
> it was on the reflector or in a direct e-mail during testing
> of some beta ALC code.
>
>> FWIW, I leave my K3's power control set at 100 watts, but I
>> adjust the mic gain control to a setting which ensures I get
>> zero ALC reading (even one bar causes a noticeable increase
>> in IMD as measured on a PSKmeter)."
>
> Setting the power out to 100 watts in PSK will guarantee that
> the final is being driven into compression on peaks if you see
> ALC (enough drive to reach 100 watts).
>
> I measure no difference in IMD with no ALC (just below the
> point at which the first bar shows) vs. five solid bars if
> the power level is kept below about 60 watts. Put another
> way, if the peak (CW equivalent) power level is kept below
> about 60 watts to prevent compression (and the onset of IMD
> generation) in the K3's finals, there is no difference with
> ALC just below the level of the first bar and five solid bars.
> If the mic/line gain is open just enough to get power output
> the PSK has more noise, has about 1 dB more IMD, and power
> output is less stable than with five bars of ALC.
>
> What Rich's procedure does accomplish is assure that the power
> output does not exceed the 50/60 watt level.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of Rob May
>> Sent: Saturday, October 04, 2008 11:03 AM
>> To: [hidden email]
>> Subject: RE: [Elecraft] Power too high in PSK31 / SSB
>>
>>
>>
>> Joe, W4TV, wrote:
>>
>>
>> Running "no bars" of ALC in PSK/AFSK causes the microphone
>> gain to be increased to compensate for the insufficient
>> drive. This will result in added distortion (noise and IMD)."
>>
>>
>>
>> Richard, VE3JAY, wrote:
>>
>>
>> FWIW, I leave my K3's power control set at 100 watts, but I
>> adjust the mic gain control to a setting which ensures I get
>> zero ALC reading (even one bar causes a noticeable increase
>> in IMD as measured on a PSKmeter)."
>>
>>
>>
>> So, no bars equals more noise and IMD or even one bar causes
>> more IMD?
>> These two statements seem to contradict each other. I'm
>> thinking that the
>> ALC will only limit mic gain, it won't bring it up if it's
>> low, other wise you wouldn't
>> have any dynamic range on your voice, the ALC would tend to
>> make everything the same level. I'll just keep doing the way
>> I've been doing it. I get good
>> reports and the power output that I expect.
>> Rob
>> NV5E
>>
>>
>>
>> _________________________________________________________________
>> See how Windows connects the people, information, and fun
>> that are part of your life.
>> http://clk.atdmt.com/MRT/go/msnnkwxp1020093175mrt/direct/01/__
> _____________________________________________
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[Steve Ward]

"Julian, G4ILO" <[hidden email]> writes:

>I have just noticed that my K3 appears to be giving vastly more peak power
>out than the value selected by the power control. I assume that this issue
>has occurred since my loading the version 2.38 production firmware after
>returning from holiday, because I did not have this problem before then.

>The constant carrier power level when TUNE is pressed appears to be correct.
>However in PSK31 mode I am getting almost full scale on the internal meter
>when 40W is dialled up. When the PSK software sends a tune signal (pure
>tone) an external power meter shows about twice the amount of power that has
>been specified. On SSB at 100W the internal meter seems to be at full scale
>most of the time as well.

>Has anyone else experienced this, and what is the solution?

I have noticed that with my setup the power level varies greatly depending on where in the passband I'm transmitting.  In other words if I setup HRD to work a QSO on a lower frequency (say between 800Hz and 1000Hz) I get a much higher indicated power output than if I work at the center (1350Hz) or higher.  I just figured this was due to the frequency response of my soundcard (SignaLink USB) and or the accuracy of the power output meter at different audio frequencies.  I'd appreciate hearing others' thoughts on this too!

Steve
AD7OG
K3 #1544


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[Julian, G4ILO]

Steve Ward wrote

I have noticed that with my setup the power level varies greatly depending on where in the passband I'm transmitting.  In other words if I setup HRD to work a QSO on a lower frequency (say between 800Hz and 1000Hz) I get a much higher indicated power output than if I work at the center (1350Hz) or higher.  I just figured this was due to the frequency response of my soundcard (SignaLink USB) and or the accuracy of the power output meter at different audio frequencies.  I'd appreciate hearing others' thoughts on this too!

You might expect that if you did not have enough drive level due to trying to use the audio level to control the power output. If you set it up as decsribed with 4 or 5 bars of "ALC" then the power control should give you a constant output until you get to the really steep part of the passband. I use the quotes deliberately - as I understand it the meter is not actually measuring ALC when in DATA A mode. Certainly I do not observe any adverse reading on my IMD meter when set up this way, with the power control set for 40W output.

Having said that, I prefer to operate at the "sweet spot" in the center of the passband. The wonderful program Fldigi has a handy QSY button that shifts whatever signal you are receiving to that point, so you can then dial in a narrow filter and get the best possible copy.

[Bob Cunnings NW8L]

Here a link to Lyles original missive:

http://n2.nabble.com/K3-Transmit-IMD-tp466326p466329.html

Bob NW8L

On Sat, Oct 4, 2008 at 10:18 AM, Joe Subich, W4TV
<[hidden email]> wrote:
>
>
> My information comes directly from Lyle - I don't remember if
> it was on the reflector or in a direct e-mail during testing
> of some beta ALC code.
>
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