Re: [Elecraft] K3/100 TX problem on 20m

[Michael Carter via Elecraft]

Hi Paul,

I'd say that our respective KPA3A TX Gain calibration
values are similar enough.  Having not had the
bipolar PA model KPA3, I don't have a point of
reference for whether your TX gain parameter
values are reasonable or not.

I would contact Elecraft Support and copy
Keith, WE6R  with
a request for their troubleshooting document
dealing with 'low TX output power.'  I don't
have a copy and only learned of its existence
by Keith mentioning it in another post.  I don't
think it's posted on the Elecraft public pages.

73,
Mike, K8CN
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Re: [Elecraft] K3/100 TX problem on 20m

[dyno lab]

Hi Mike,

Thanks for the gain information.
I am going to look at the the gain numbers and see if there is any correlation 
with the wildly different input impedances to the output lowpass filters.

For reference, I found the input Z to the filters to be as follows:
160: 63.8 +J1.6
80:  35.7 +J5.1
40:  42.0 +J5.8
20:  32.0 -J2.1
17:  51.0 +J3.1
15:  49.6 -J0.3
10:  60.4 -J2.9
6:   51.0 +J0.14

Looking at the component values of the output filters, it appears that the 
above impedances were by design. Which makes me wonder if it was an attempt to 
compensate for the poor saturation characteristics of the MOSFETs and leakage 
inductance of the output transformer of the MOSFET amplifier (KPA3A)?

I am also finding in some cases that the K3s LPA (KLPA3A) has some problems of 
its own and does not like to play nicely with the input to the LDMOS K3s 
Retrofit Amplifier on 160 meters.
I would however like to avoid redesigning LPA by compensating for its 
shortcomings in the LDMOS amplifier.

Thanks again for your feedback.
73,
Hal
W7YNC  


> On 03/06/2024 3:07 PM PST Michael Carter via Elecraft 
>  wrote:
> 
>  
> Hi Paul,
> 
> For comparison, here are the 50 watt TX gain values from the
> calibration I did last November when I installed
> the KPA3A 100 watt PA in my K3 (s/n 67xx):
> 
> 1900 kHz TXGain HP  10
> 3750 kHz TXGain HP  06
> 5336 kHz TXGain HP  08
> 7150 kHz TXGain HP  08
> 10125 kHz TXGain HP  08
> 14200 kHz TXGain HP  05
> 18110 kHz TXGain HP  05
> 21200 kHz TXGain HP  03
> 24930 kHz TXGain HP  03
> 29000 kHz TXGain HP  05
> 52000 kHz TXGain HP  04
> 
> Do you know if your 100 watt PA module
> uses RF bipolar transistors or MOSFETs
> (the KPA3A uses MOSFETs; the original KPA3
> uses bipolars)?
> I don't know if the MOSFET version has higher gain
> than the bipolars, but I suspect not.
> 
> I've been in a separate conversation
> with Hal, W7YNC, who is an LDMOS RF amplifier
> designer professionally.  There is some
> uncertainty about whether the higher TX gain
> parameters mean higher TX drive signal
> amplitude or the converse.
> 
> In any event, your TX gain values don't
> have wild swings from band to band,
> although the difference between 20
> meter and 30 meter gains is substantial.
> 
> Perhaps some others who have done
> TX gain calibrations recently (or could
> repeat them) on K3 units with the
> bipolar PA transistors could post
> their results?
> 
> 73,
> Mike, K8CN
> 
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[Elecraft] K3/100 TX problem on 20m

[James Holohan]

Hi. I had this problem in the recent past. It turned out to be an issue with my 
multiband yagi. It only occurred on 20m.
Hope this helps.
Jim EI4HH.

[https://s-install.avcdn.net/ipm/preview/icons/icon-envelope-tick-green-avg-v1.png]
 
Virus-free.www.avg.com
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[Elecraft] K3/100 TX problem on 20m

[Paul Kent]

Thanks again, Mike.
My K3 has the bipolar 100w PA.

I also have a properly-functioning K3S/100 with the CMOS PA. Just for 
comparison I ran the HP TX gain calibration on the K3S and it produced these 
numbers:

160m/19
80m/08
60m/10
40m/12
30m/13
20m/08
17m/08
15m/05
12m/10
10m/10
6m/06

The numbers are significantly different from those of the K3 but that probably 
doesn’t mean much. I even thought about swapping the PA modules between the K3 
and K3S as a test but they are not compatible for a direct swap.

Paul, K0PK

Sent from Mail for Windows

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Re: [Elecraft] K3/100 TX problem on 20m

[Michael Carter via Elecraft]

Hi Paul,

For comparison, here are the 50 watt TX gain values from the
calibration I did last November when I installed
the KPA3A 100 watt PA in my K3 (s/n 67xx):

1900 kHz TXGain HP  10
3750 kHz TXGain HP  06
5336 kHz TXGain HP  08
7150 kHz TXGain HP  08
10125 kHz TXGain HP  08
14200 kHz TXGain HP  05
18110 kHz TXGain HP  05
21200 kHz TXGain HP  03
24930 kHz TXGain HP  03
29000 kHz TXGain HP  05
52000 kHz TXGain HP  04

Do you know if your 100 watt PA module
uses RF bipolar transistors or MOSFETs
(the KPA3A uses MOSFETs; the original KPA3
uses bipolars)?
I don't know if the MOSFET version has higher gain
than the bipolars, but I suspect not.

I've been in a separate conversation
with Hal, W7YNC, who is an LDMOS RF amplifier
designer professionally.  There is some
uncertainty about whether the higher TX gain
parameters mean higher TX drive signal
amplitude or the converse.

In any event, your TX gain values don't
have wild swings from band to band,
although the difference between 20
meter and 30 meter gains is substantial.

Perhaps some others who have done
TX gain calibrations recently (or could
repeat them) on K3 units with the
bipolar PA transistors could post
their results?

73,
Mike, K8CN

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[Elecraft] K3/100 TX problem on 20m

[Paul Kent]

Sent from Mail for Windows
Thanks, Mike.

The 50w TX gain numbers are: 160m/32, 80m/36, 60m/48, 40m/40, 30m/32, 20m/18, 
17m/11, 15m/08, 12m/05, 10m/05, 6m/02

Paul, K0PK
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Re: [Elecraft] K3/100 TX problem on 20m

[Masadaman via Elecraft]

I don't want to be here

Yahoo Mail: Search, Organize, Conquer 
 
  On Tue, Mar 5, 2024 at 9:15 AM, Paul Kent wrote:   
My K3/100 gives a high DC current warning when transmitting on 20m with power 
settings above 75 watts. Maximum output is about 80 watts and is unstable. All 
other bands perform normally with full 100w output and normal current draw. (50 
ohm dummy load) I have done the TX gain and wattmeter calibrations, finding no 
issues and with no change in symptoms. The output LPF is shared with 30m and I 
replaced all the capacitors in that circuit, also with no change in symptoms. 
Any ideas on what may be causing this problem?
Paul, K0PK
Sent from Mail for Windows

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Re: [Elecraft] K3/100 TX problem on 20m

[Masadaman via Elecraft]

This thread sucks...

Yahoo Mail: Search, Organize, Conquer 
 
  On Tue, Mar 5, 2024 at 11:29 AM, Michael Carter via 
Elecraft wrote:   Hi Hal,

The numbers themselves have meaning to the
DACs inside the K3, but in terms of actual
units I don't know.  The key thing is that as
those values are increased, the drive levels
from the TX DACs are increased, though I
don't know if the relationship is a linear one.

The gains of the LPA and PA stage transistors
fall off at higher frequencies, so one might
expect TX Gain parameters on those bands
to be somewhat higher than on the low bands.
However, if two immediately adjacent bands
have very different TX gain parameter values,
the likelihood is that something is amiss
in one of the filters (either BPF or LPF) and
the associated relays that select the filters.

73,
Mike, K8CN

From: dyno lab 
Sent: Tuesday, March 5, 2024 11:19 AM
To: Michael Carter ; Michael Carter via Elecraft 

Subject: Re: [Elecraft] K3/100 TX problem on 20m

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Do the TX gain parameter numbers have meaning such as dB or are they just 
relative numbers ?

73,
Hal
W7YNC


> On 03/05/2024 6:35 AM PST Michael Carter via Elecraft 
>  wrote:
>
>
> Hi Paul,
>
> Could you please post the TX gain parameters
> recorded by the K3 Utility at the 50 watt level
> for all bands?
>
> If there is a significant difference in those gain
> parameter values between adjacent bands (say
> 30 and 17 meters) and the value on the 20
> meter band, that may be an additional clue.
>
> The bandpass filter bank may be at issue here
> since you've checked the appropriate LPF.
> If there's a problem with the relay contacts
> on the relevant BPF or LPF section, that may
> also reduce the TX signal level and force
> an elevated TX Gain parameter value for that
> band.
>
> Keith, WE6R has a checklist of steps to
> try when diagnosing low TX output power.
> I recall he said to contact supp...@elecraft.com
> for that document.
>
> 73,
> Mike, K8CN
> __
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Re: [Elecraft] K3/100 TX problem on 20m

[Michael Carter via Elecraft]

Hi Hal,

The numbers themselves have meaning to the
DACs inside the K3, but in terms of actual
units I don't know.  The key thing is that as
those values are increased, the drive levels
from the TX DACs are increased, though I
don't know if the relationship is a linear one.

The gains of the LPA and PA stage transistors
fall off at higher frequencies, so one might
expect TX Gain parameters on those bands
to be somewhat higher than on the low bands.
However, if two immediately adjacent bands
have very different TX gain parameter values,
the likelihood is that something is amiss
in one of the filters (either BPF or LPF) and
the associated relays that select the filters.

73,
Mike, K8CN

From: dyno lab 
Sent: Tuesday, March 5, 2024 11:19 AM
To: Michael Carter ; Michael Carter via Elecraft 

Subject: Re: [Elecraft] K3/100 TX problem on 20m

[You don't often get email from dyno...@comcast.net. Learn why this is 
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Do the TX gain parameter numbers have meaning such as dB or are they just 
relative numbers ?

73,
Hal
W7YNC


> On 03/05/2024 6:35 AM PST Michael Carter via Elecraft 
>  wrote:
>
>
> Hi Paul,
>
> Could you please post the TX gain parameters
> recorded by the K3 Utility at the 50 watt level
> for all bands?
>
> If there is a significant difference in those gain
> parameter values between adjacent bands (say
> 30 and 17 meters) and the value on the 20
> meter band, that may be an additional clue.
>
> The bandpass filter bank may be at issue here
> since you've checked the appropriate LPF.
> If there's a problem with the relay contacts
> on the relevant BPF or LPF section, that may
> also reduce the TX signal level and force
> an elevated TX Gain parameter value for that
> band.
>
> Keith, WE6R has a checklist of steps to
> try when diagnosing low TX output power.
> I recall he said to contact supp...@elecraft.com
> for that document.
>
> 73,
> Mike, K8CN
> __
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Re: [Elecraft] K3/100 TX problem on 20m

[dyno lab]

Do the TX gain parameter numbers have meaning such as dB or are they just 
relative numbers ?

73,
Hal
W7YNC


> On 03/05/2024 6:35 AM PST Michael Carter via Elecraft 
>  wrote:
> 
>  
> Hi Paul,
> 
> Could you please post the TX gain parameters
> recorded by the K3 Utility at the 50 watt level
> for all bands?
> 
> If there is a significant difference in those gain
> parameter values between adjacent bands (say
> 30 and 17 meters) and the value on the 20
> meter band, that may be an additional clue.
> 
> The bandpass filter bank may be at issue here
> since you've checked the appropriate LPF.
> If there's a problem with the relay contacts
> on the relevant BPF or LPF section, that may
> also reduce the TX signal level and force
> an elevated TX Gain parameter value for that
> band.
> 
> Keith, WE6R has a checklist of steps to
> try when diagnosing low TX output power.
> I recall he said to contact supp...@elecraft.com
> for that document.
> 
> 73,
> Mike, K8CN
> __
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Re: [Elecraft] K3/100 TX problem on 20m

[Michael Carter via Elecraft]

Hi Paul,

Could you please post the TX gain parameters
recorded by the K3 Utility at the 50 watt level
for all bands?

If there is a significant difference in those gain
parameter values between adjacent bands (say
30 and 17 meters) and the value on the 20
meter band, that may be an additional clue.

The bandpass filter bank may be at issue here
since you've checked the appropriate LPF.
If there's a problem with the relay contacts
on the relevant BPF or LPF section, that may
also reduce the TX signal level and force
an elevated TX Gain parameter value for that
band.

Keith, WE6R has a checklist of steps to
try when diagnosing low TX output power.
I recall he said to contact supp...@elecraft.com
for that document.

73,
Mike, K8CN
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[Elecraft] K3/100 TX problem on 20m

[Paul Kent]

My K3/100 gives a high DC current warning when transmitting on 20m with power 
settings above 75 watts. Maximum output is about 80 watts and is unstable. All 
other bands perform normally with full 100w output and normal current draw. (50 
ohm dummy load) I have done the TX gain and wattmeter calibrations, finding no 
issues and with no change in symptoms. The output LPF is shared with 30m and I 
replaced all the capacitors in that circuit, also with no change in symptoms. 
Any ideas on what may be causing this problem?
Paul, K0PK
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