[hpsdr] Star-10 Transceiver article in QEX

[Chris Stratton]

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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