[hpsdr] Star-10 Transceiver article in QEX

[Robert McGwier]

Yes, my reaction to the article would seem to be an overreaction.  If
that were all I was reacting to, I would apologize. I will not be
apologizing at all.  I have yet to decide on how my actions will proceed
from here.  It will depend almost completely on the reaction of QEX to
the article and the critique it has received.

Multiple people tried very nicely to point out the possible problems in
the article.  The nicest thing Drentea said to them was that they were
idiots.  I blew a gasket when he told several PROFESSIONAL SDR engineers
that they were idiots (none of them was me) and told them they could not
run the right end of a Laplace transform.

Bob



Chris Stratton wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Robert McGwier rwmcgwier at gmail.com wrote:
> 
>> Having never seen any of Drentea's measurements of
> his >own radio, I cannot attest to the credibility of
> his 
>> measurements but I do have a comment.  As a person
> who >works professionally to do software radio for the
> U.S. >government, I do not know of a lab that can
> measure 150 >dB of IMD dynamic range.  
> 
> I've only had a chance to skim the article and look at
> the numbers, but my general impression is that this
> guy is using terms in very non-standard ways.
> 
> His 150 dB dynamic range is not instantaneous dynamic
> range as we know it (that would be hard), but the
> range of input signals which his system can accept
> when it's AGC loops are allowed to do their job.
> 
> Looking at his minimum discernible signal claim of
> -132 to -136 dBm, it becomes clear that this is a
> signal which will produce a signal to noise ratio of
> ZERO.
> Take -174 dBc/Hz of thermal noise, add 27 to convert
> to power in his 500 Hz bandwidth, and that's -147 dBm
> noise floor as he claims in one of his charts.  The
> problem is that the the difference between this -147
> and the -132 signal is entirely taken up by his noise
> figure... in other words, his signal is of equal power
> to the noise.  The standard MDS measurement is to a 10
> dB SNR, which means we derate his claim to -122.  For
> a 500 Hz bandwidth that's not particularly impressive,
> as indeed a 15 dB noise figure is nothing special, and
> the 12 dB he sometimes got is merely comparable to
> other well designed receivers.  
> 
> If the digital design doesn't contain errors, it
> basically all comes back to the front end noise
> figure... you can't get better than the physics, you
> can only make it worse by making design mistakes.
> 
> Chris
> 
> 
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-- 
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
“An optimist may see a light where there is none, but why
must the pessimist always run to blow it out?” Descartes

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