[hpsdr] Not Hpsdr - A Front-End with an IIP3 > +50dBm ?

[Bob McGwier]

Indeed, especially if you compute IP3 the way the ARRL labs does, by 
raising the level of the two tones injected into the DUT until they 3rd 
order product gets to be S5.  That would be really really difficult with 
the test equipment they have and a front end with a "50 dBm IP3" and for 
most radios to take that much signal, but let's suppose they did it.

It appears from this test that the IP3 and the IMD-DR dynamic range are 
large.   However,  if dynamic range, which is the more important thing 
takes into account the rise in the noise floor induced by the two tones 
or a single tone,  the dynamic range is more limited than would be 
indicated by the ARRL test method.

I refer interested readers to the Sherwood test table:

http://www.sherweng.com/table.html

I then suggest that ARRL members compare the numbers Sherwood has 
measured to those measured by the ARRL labs for the 
receivers/transceivers that are compared.   You will see that inevitably 
the dynamic range numbers are lower than those measured in the ARRL labs 
because Sherwood takes LO phase noise into consideration.  You will see 
MANY entries in his table where they are footnoted with "phase noise and 
not IMD limited".

I think his Ip3 numbers have been computed from the DR measurement when 
the more accurate way to compute IP3 is the S5 test but I would rather 
he compute USABLE IP3 and the imputed dynamic range by taking LO phase 
noise into account than the other way around.

As usual, Ulrich is right on the money here.

For the superior transceiver being built by Cornell Dentra and being 
written up in QEX (and which many know about from his writing and web 
page), he does get there with oscillators that have sufficiently low 
phase noise to use it.  You cannot even begin to figure out how much it 
would cost to build such a thing.  He uses parts that were used in 
serious projects and then surplussed and for which the government or 
commercial entity paid a boat load of bucks. You might be able to 
duplicate his work if you had the resources of Bill Gates or Warren 
Buffet to throw around.  It is not reproducible (though it is brilliant).

Bob
N4HY

KA2WEU at aol.com wrote:
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> Given the current SSB Phase noise of oscillators, this IP3 is useless.
>  
> 73 de Ulrich
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-- 
Robert W. McGwier, Ph.D.
Center for Communications Research
805 Bunn Drive
Princeton, NJ 08540
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