TX IMD problem

[chen dave]

Hello All,

    I checked my K3's TX IMD today(K3 SN:1302), from 5W to 110W. Very good
TX IMD when I set the output power to 35w( 50db), but very poor when I set
it to 100w or 110w(20~18db).

  Any one can help?
  I have about 10 photos for this test, if interest I can send via email
offline.

BTW: I use 32A DAIWA PS.

--

--------------------------------
All the best!

David,ba4rf
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[Jan Erik Holm]

I have measured myself however didn´t come up
with as poor and/or as good numbers.

What could be interesting is with what and how
did you measure.

/ Jim SM2EKM
-----------------
chen dave wrote:

> Hello All,
>
>     I checked my K3's TX IMD today(K3 SN:1302), from 5W to 110W. Very good
> TX IMD when I set the output power to 35w( 50db), but very poor when I set
> it to 100w or 110w(20~18db).
>
>   Any one can help?
>   I have about 10 photos for this test, if interest I can send via email
> offline.
>
> BTW: I use 32A DAIWA PS.
>

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[chen dave]

Hi Jim,

    I use K3 internal 2 tones test function + SDR-IQ+ SpectraVue3.  If need
I can use HP RF spectrum monitor to test it.
    http://photo.blog.sina.com.cn/u/1411826944  for test photos.

73 de ba4rf,David



2010/4/4 Jan Erik Holm <[hidden email]>

> I have measured myself however didn´t come up
> with as poor and/or as good numbers.
>
> What could be interesting is with what and how
> did you measure.
>
> / Jim SM2EKM
> -----------------
> chen dave wrote:
> > Hello All,
> >
> >     I checked my K3's TX IMD today(K3 SN:1302), from 5W to 110W. Very
> good
> > TX IMD when I set the output power to 35w( 50db), but very poor when I
> set
> > it to 100w or 110w(20~18db).
> >
> >   Any one can help?
> >   I have about 10 photos for this test, if interest I can send via email
> > offline.
> >
> > BTW: I use 32A DAIWA PS.
> >
> ______________________________________________________________
> 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
>

--

--------------------------------
All the best!

David,ba4rf
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[Kok Chen]

On Apr 4, 2010, at 4/4    6:50 AM, chen dave wrote:

> I use K3 internal 2 tones test function + SDR-IQ+ SpectraVue3.

Are you ignoring the crest factor of the two tone test signal?

To get 100 watts average RF power from a "two tone" signal, the  
instantaneous peak power has to be nearly 200 watts.  Assuming that  
you are not clipping the A/D converter of the receiver, I suspect that  
your K3's PA may either be clipping on the voltage rail or the PA is  
being ALC'ed.

This is why when I tested the PSK31 transmit IMD on my K3 (here: http://homepage.mac.com/chen/Technical/K3/Digital/digital.html 
  ), I had limited the output (average) RF power to 50 watts.

Note that when BPSK31 (or QPSK31) transmits the idle Varicode, it is  
precisely a "two-tone" signal (i.e., double sideband suppressed  
carrier signal that is modulated by a sinusoidal AF tone).  In the  
case of PSK31, the AF tone is a sine wave at 15.625 Hz (the I and Q  
signals are cosinusoidally varying between each PSK31 symbol at a  
period of 31.25 symbols/sec).

73
Chen, W7AY

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