[hpsdr] MDS and related architectures

[k3bu at optonline.net]

>>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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