[hpsdr] MDS and related architectures

[Robert McGwier]

Yuri:

The ARRL in its review of the SDR-1000 said it was amongst the best 
receivers they had ever measured at close in dynamics.  In fact  they 
measured the receiver at 500 Hz spacing.  They could not measure the 
IMD-DR and IP3 any closer than this because their laboratory equipment 
was not up to the challenge.   But at that spacing,  IT IS the best 
receiver they have ever measured.  It outperforms EVERY receiver on the 
Sherwood Engineering page at 500 Hz.  It has a measure IP3 of 30 dBm and 
a dynamic range of 98 dB at 500 Hz according to the ARRL labs.  I still 
personally dispute the ARRL measurements since my own personal 
measurements done with my own laboratory equipment give +32 dBm and 104 
dB IMD-DR.  Gerald has repeated these experiments in the Flex lab 
without my having told him my results.  I am using a high end sound card 
and I suspect that this has a tremendous impact on it that I have yet to 
fully understand (even  my favorite Agilent program does not understand 
it!).  We are building the AKM5394A codec based devices now that will 
equal this high end sound card (it uses that chip) but we have optimized 
the design for our purposes (Jason and ultimately the ISD detector).   
While I would admit that sometimes theory does not equal what is found 
in practice,  I believe that the sampler/integrator front ends would 
continue to perform well at 2 Hz spacing!  Your statement that SDR is 
not up to snuff yet on the RX is demonstrably incorrect and the proof 
has been supplied by an outside agency in the ARRL labs if you choose 
not to believe our own numbers.


73's
Bob
N4HY


k3bu at optonline.net wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>   
>
> ------------------------------------------------------------------------
>
> >>Present receivers have dynamic range specified at about 20 kHz and 2 
> KHz, with state of the art SFDR around 95 dB and 75 dB respectively.  
> The close in dynamic range measurement shows the limited performance 
> of the 2nd IF within the passband of the roofing filter.  With a 
> Mercury style SDR, the close in dynamic range never changes, the 
> design gets close 100 dB all to way to zero offset. 
>
> The new SDR specification will look more like 130 dB SFDR at 10% off 
> frequency (due to the preselector) and 100 dB SFDR any offset from 0 
> to about 1-3% of frequency (in the passband of the preselector).
>
> jeff, wa1hco<<
>
>  
>
> I am looking forward to all this wunder stuff, just that from the past 
> experience, especially when the brutal signals are present from other 
> bands and within the band, even 2 kHz spacing specification doesn't 
> tell the real picture.
>
> Actually I was thinking of way of testing, more reflecting the real 
> life - rather than test at spacings of 20 or 2 kHz, use signal levels 
> of x, y, z and see how close we can get to the "signal in the noise" 
> without "humping" it. For serious contesting we are looking at 
> spacings of 200 Hz on CW. Again, there are two major situations, 
> strong signals from other bands and strong signals within the band.
>
> I guess the point is, if the pure SDR stuff doesn't cut it (yet?), we 
> should have the extra options available at the "switch" to kick in as 
> needed. Most likely candidate for the separate module.  By all means 
> let's have the most immune mixer with cleanest injection signals with 
> lowest possible phase noise.
>
> Yuri Blanarovich, K3BU, VE3BMV
>
>
> ------------------------------------------------------------------------
>
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-- 
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
"You see, wire telegraph is a kind of a very, very long cat.
You pull his tail in New York and his head is meowing in Los
Angeles. Do you understand this? And radio operates exactly
the same way: you send signals here, they receive them there.
The only difference is that there is no cat." - Einstein


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