Re: K3 S/N 222: Poor PSK31 IMD levels on 10m

[Greg - AB7R]

Hi Julian.  You should be seeing readings around -30 or better.

Are you using PSK-D with the paddles or a soundcard program with Data-A?

Set your soundcard output level to about 30-40%.  Then with the K3 in  
Data/Data-A mode start with the line-in gain at 1(MIC gain control  
becomes Line-in control in data mode).  Set your power to about 25W  
and while sending some text adjust the line in gain so that you have  
about 3 bars of ALC.
The only thing I have seen that causes excessive IMD is overdriving  
either the soundcard output and/or too much line-in gain.

73
Greg
AB7R

On May 2, 2009, at 8:16 AM, Julian Moss wrote:

> Hi!
>
> I have a problem with my K3 S/N 222. I have just begun using my K3 on
> 10m PSK31 after getting interested in using the PSK Propagation
> Reporter to detect sporadic-e openings.
>
> I was making only my second contact on 10m PSK31 this afternoon and
> the station I was working gave me a very poor IMD report. I switched
> on my KK7UQ IMD meter and sure enough the IMD was very poor, not quite
> as bad as the station reported but showing values such as -15dB etc.
>
> IMD is still very good on the higher bands (I did not check 24MHz
> because I don't have an antenna for it) so I do not think this is a
> fault that has suddenly developed.
>
> It is not a problem with RF feedback on 10m because I checked the IMD
> whilst using my DL1 dummy load and it was still unacceptably bad.
>
> It is not a problem with the KK7UQ meter giving false readings on 10m
> because it shows readings in the -30dB region when I use another radio
> on 10m.
>
> It is probably not a problem with the KPA100 because the bad IMD
> readings occur even at 5W (and even lower) power level.
>
> It is probably not a new problem, as I have hardly ever used the K3 on
> 10m since I had it, and never on PSK31 on 10m, so no-one would have
> noticed it before.
>
> Is there anything that can be done, bearing in mind that the only test
> equipment I have that can show the IMD is the KK7UQ meter?
>
> 73,
>
> Julian, G4ILO
> G4ILO's Shack: www.g4ilo.com
> G4ILO's Blog: www.g4ilo.com/blog.html

... [show rest of quote]

______________________________________________________________
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

[Dave, G4AON]

I was in contact with Julian yesterday and the problem seems to be
related to the computer sound card to line in/out cable. He's not sure
at this stage if it's rear panel grounding issues or not.

Measuring my K3's 2 tone IMD using the internal 2 tone generator, gives
3rd order products of -33 dB relative to one of the two tones (or -39 dB
as per the ARRL method of measurement) on 28 MHz at a power output level
of 30 Watts. Julian was using a power level of 20 ~ 30 Watts. The
figures are much worse when driving the low power PA hard at 10 Watts,
or the high power PA at 100 Watts.

73 Dave, G4AON
K3/100 #80
==================

>/ I was making only my second contact on 10m PSK31 this afternoon and
/>/ the station I was working gave me a very poor IMD report. I switched
/>/ on my KK7UQ IMD meter and sure enough the IMD was very poor, not quite
/>/ as bad as the station reported but showing values such as -15dB etc.
/>/ /
______________________________________________________________
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