[CQ-Contest] SDR Mythbusters - ADC Overload myths debunked...

[Jim Brown]

On Mon,11/9/2015 9:41 AM, Mark van Wijk, PA5MW wrote:
> The NPR test is flawed because of its reference MDS. 

The fundamental idea of the NPR test is a VERY good one -- properly 
done, NOT with a sliding reference level, is to expose the contribution 
of spurs and phase noise. It is the "sliding reference level" -- that 
is, each radio is tested with different amplitude test signal based on 
its characteristics -- that makes Adam's work fundamentally flawed.

There are many very nice things about SDRs, but they have two Achillies' 
Heels -- 1) dynamic range of their input stage is not great enough for 
most contesting, and 2) their User Interfaces are not geared to 
contesting. There is, of course, room for improvement on both fronts.

#1 can be eliminated for overload by out of band signals by a 
preselector front end, or by RX bandpass filters. But that does NOTHING 
for in-band overload, like 40M SSB in EU and AS, or at a M/M with two TX 
on the same band. The current hardware limitation within the SDR is that 
they exploit parts manufactured for the cell phone industry, which, by 
virtue of high mfg volume, offer great performance at low cost. But they 
have 10-15 dB less dynamic range than is required, and parts that do 
that cost a LOT more.

#2 can be overcome by coordination between those who tell the 
programmers what to do and those who use actually use radios on the air. :)

My neighbor, NR0V, author of the Pure Signal distortion reduction 
system, demonstrated for me a new noise reduction algorithm he's written 
for Power SDR, using the RX of the new inexpensive ANAN 10E on 40M SSB 
during the day. I was VERY impressed -- great noise reduction, very 
natural sounding with minimal artifacts. Certainly I'd like to hear it 
under contest conditions. :)

Meanwhile, some impressive remote and contesting stations are being 
built with Flex 6700s, and I'm hearing positive comments from users. 
Like all new products and ways of doing things, it takes time for us to 
learn to use them, for mfrs to understand our needs and make them 
better. My first station consisted of an truly awful Hallicrafters S38D 
and BC459 CW TX (WW II surplus).

73, Jim K9YC