K3 :: slightly reduced TX power output noticed

[Steve Jackson-5]

Hello

I noticed CW output power on 40M was off by a small amount, 7-10%.  (Was set to 100W.)  

Meters are Bird 43 and LP-100.  2 kW dummy load has mondo return loss (26 dB).

So, I went to see what the 40 meter HP TX gain setting was, and it seems like it was topped out.  

K3 didn't quite make the same power it did before, maybe 8% low.  Odd, so, I cranked the TXG setting to 60, which is max.  

Still didn't quite make 50W.  Then I noticed that the gain setting reverted back to 58 without my input.  Huh?

Turned the TX ALC back on, then checked TX out on 40M at 50W ... and got 50 watts.  Cool.  But ~7 watts low at 100W setting.

HP TX gain setting, for comparison, on 20M is 24.  It's like it has no headroom on 40M.  My K2 was hottest on 40, IIRC.

Checked power on 20M at 50W, right on the money.  At 100W, 7-10% low, and much the same on other bands.

Internal voltmeter shows 13.6V on RX and 12.9V on TX @ 100W setting, drawing 17.7A for 94W out on 7050.  

50W out setting yields 50.4W RF at 13.15A @ 13.1V.  

Power source is an Astron RS-35M across three 105A-h AGM batteries, and nothing smaller than 10AWG in between.  

West Mountain Radio crimper tool assembled PowerPoles, the shack standard here for years.  

Probably have 100s of them.  I don't think this is an I^2R problem.

All 3 RF wattmeters agree at 50W.

FWIW I just upgraded to the new firmware this evening.  

Since 92 watts equals 100 in my book and because at 50W the set makes 50W, this isn't too much of a concern.  However, I thought I'd bring it up in case the observation is indicative of something else that actually does matter.

Steve KZ1X/4
K3 #1209


     
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[Steef PA2A]

When I make keydown at the 120 Watt level on 20 meters, the message HI CUR
appears after about 10 seconds and the power goes to 106 watts. I did not
see that before.

73 's Steef PA2A
k3 #1184

----- Original Message -----
From: "Steve Jackson" <[hidden email]>
To: <[hidden email]>
Sent: Friday, July 25, 2008 5:51 AM
Subject: [Elecraft] K3 :: slightly reduced TX power output noticed

>
> Hello
>
> I noticed CW output power on 40M was off by a small amount, 7-10%.  (Was
> set to 100W.)
>
> Meters are Bird 43 and LP-100.  2 kW dummy load has mondo return loss (26
> dB).
>
> So, I went to see what the 40 meter HP TX gain setting was, and it seems
> like it was topped out.
>
> K3 didn't quite make the same power it did before, maybe 8% low.  Odd, so,
> I cranked the TXG setting to 60, which is max.
>
> Still didn't quite make 50W.  Then I noticed that the gain setting
> reverted back to 58 without my input.  Huh?
>
> Turned the TX ALC back on, then checked TX out on 40M at 50W ... and got
> 50 watts.  Cool.  But ~7 watts low at 100W setting.
>
> HP TX gain setting, for comparison, on 20M is 24.  It's like it has no
> headroom on 40M.  My K2 was hottest on 40, IIRC.
>
> Checked power on 20M at 50W, right on the money.  At 100W, 7-10% low, and
> much the same on other bands.
>
> Internal voltmeter shows 13.6V on RX and 12.9V on TX @ 100W setting,
> drawing 17.7A for 94W out on 7050.
>
> 50W out setting yields 50.4W RF at 13.15A @ 13.1V.
>
> Power source is an Astron RS-35M across three 105A-h AGM batteries, and
> nothing smaller than 10AWG in between.
>
> West Mountain Radio crimper tool assembled PowerPoles, the shack standard
> here for years.
>
> Probably have 100s of them.  I don't think this is an I^2R problem.
>
> All 3 RF wattmeters agree at 50W.
>
> FWIW I just upgraded to the new firmware this evening.
>
> Since 92 watts equals 100 in my book and because at 50W the set makes 50W,
> this isn't too much of a concern.  However, I thought I'd bring it up in
> case the observation is indicative of something else that actually does
> matter.
>
> Steve KZ1X/4
> K3 #1209
>
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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>
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> Elecraft web page: http://www.elecraft.com 

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[N0QO]

I have also noticed a reduction in peak power on many bands.  It generally starts as approx a 1dB reduction and can eventually progrees to approx 3 dB.  I did submit a post regarding this but it did not go out to the mailing list fro some reason.  I will attempt to paste it below.

73, Ken N0QO

N0QO wrote

Hello, This is my first post to this group.

Has any other K3 owners experienced the something similar to what I will attempt to describe below?

At times I am noticing a reduction in peak talk power by as much as 50% below what would be expected at any given power setting.  I am measuring this in an LP100A and it is also noticeable on the internal K3 meter. I have noticed this with both the low power and high power amps.

This generally does not occur key down!  Although key down via the tune button does seem to temporarily resolve it.  I am able to replicate it easily on 10M.  If I switch to that band and I am not getting the expected peak power I can then hold the tune button and after tapping the tune button to get out of the TX cw mode I have the talk power I expect.  If I change bands say to 12M and come back to 10m the power is again below what it should be and I repeat the process above and all is well.  I have seen this on all the bands I operate which are 80-6m.  .

I have gone through the power calibration process several times and it does seem to give some temporary relief but it always comes back.  I also noticed another post that may be related where someone suggested that the LPA board may need to be reseated so I tried that with no change in results

I have a K3 ser. number 1047, 100W, no ATU, no external audio processing and am currently running the 2.02 firmware and associated DSP.  I have also tried all of the Beta release with no noticeable difference.

73, Ken N0QO

Steve Jackson-5 wrote

Hello

I noticed CW output power on 40M was off by a small amount, 7-10%.  (Was set to 100W.)  

Meters are Bird 43 and LP-100.  2 kW dummy load has mondo return loss (26 dB).

So, I went to see what the 40 meter HP TX gain setting was, and it seems like it was topped out.  

K3 didn't quite make the same power it did before, maybe 8% low.  Odd, so, I cranked the TXG setting to 60, which is max.  

Still didn't quite make 50W.  Then I noticed that the gain setting reverted back to 58 without my input.  Huh?

Turned the TX ALC back on, then checked TX out on 40M at 50W ... and got 50 watts.  Cool.  But ~7 watts low at 100W setting.

HP TX gain setting, for comparison, on 20M is 24.  It's like it has no headroom on 40M.  My K2 was hottest on 40, IIRC.

Checked power on 20M at 50W, right on the money.  At 100W, 7-10% low, and much the same on other bands.

Internal voltmeter shows 13.6V on RX and 12.9V on TX @ 100W setting, drawing 17.7A for 94W out on 7050.  

50W out setting yields 50.4W RF at 13.15A @ 13.1V.  

Power source is an Astron RS-35M across three 105A-h AGM batteries, and nothing smaller than 10AWG in between.  

West Mountain Radio crimper tool assembled PowerPoles, the shack standard here for years.  

Probably have 100s of them.  I don't think this is an I^2R problem.

All 3 RF wattmeters agree at 50W.

FWIW I just upgraded to the new firmware this evening.  

Since 92 watts equals 100 in my book and because at 50W the set makes 50W, this isn't too much of a concern.  However, I thought I'd bring it up in case the observation is indicative of something else that actually does matter.

Steve KZ1X/4
K3 #1209


     
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