Re: FDM-DUO overload issues


Clint Chron
 

Hi Steve,

 

That sounds good.  I also have a Perseus receiver and notice no difference in overload performance when compared with my Duo.  The Perseus does have front end receiver band pass filters.

 

There is a controversy in the industry on how to test SDR radios for receiver overload.  The classical approach using 3rd order IMD testing does not really work good for SDR radios.  One can actually measure several different overload points on a SDR radio, depending upon the test signal injection level.  The recommended approach is to use NPR (noise power ratio) as fully explained by Adam Farson.

 

https://www.ab4oj.com/test/docs/npr_test.pdf

 

I regularly use NPR testing on my various analog and SDR radios.  The Elad Duo, even without front end receiver band pass filters, is among some of the best receivers out there – including Flex, Yaesu, and Icom.

 

73

Clint

W7KEC

 

 

 

From: EladSDR@groups.io [mailto:EladSDR@groups.io] On Behalf Of Steve Knell
Sent: Wednesday, May 27, 2020 3:11 PM
To: EladSDR@groups.io
Subject: Re: [EladSDR] FDM-DUO overload issues

 

Many thanks for all the suggestions everyone.  I will do some more detailed analysis on this to see if there is some other reason for the issues I'm experiencing.  I did have a weird issue with my linear a while back, so I'll try taking that out of line when I get the breakthrough issue again.  I just found a Sherwood report on the FDM-DUO and he measured the dynamic range at 70dB.  He also mentioned 'high pitched stopband leakage' which is exactly what I get on 40M CW.

  "Even more strange is the leakage in the stopband. No phase noise measurement could be
  made in a 500-Hz bandwidth when tuned 2.5 kHz offset from the test signal due to filter
  leakage. Additionally, one can clearly hear high-pitched leakage out to 9.5 kHz with the
  500-Hz CW bandwidth when injecting an S9+40 dB signal (-33 dBm)."

https://www.dj0ip.de/sherwood-forest/sherwood-hf-xcvr-tests/elad-ftm-duo/

Many Thanks,
Steve

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