[TenTec] TenTec] SDR-1000 MDS

[Dr. Gerald N. Johnson]

On Sat, 2006-07-15 at 23:25 -0700, Lee A Crocker wrote:
> Jerry
> 
> I don't know anything about the FT 857.  I have had
> many rigs that used crystal/mechanical filters that
> distorted the signal and were virtually useless at
> extremely narrow bandwidths.  

Some filters do ring on noise and fast CW. The vintage Collins S-line
filter is one of those. The Collins mechanical filter for the FT-857D is
much better. The 270 Hz Kenwood filter in the TS430 was bad that way.
> 
> I have had other rigs that used DSP that were marginal
> at best.  The Pegasus comes to mind.  I don't even
> find the DSP in the Orion to be very effective except
> for the filtering function and the tunability of the
> AGC.  Those 2 aspects of the DSP are invaluable.  I
> don't find the 100 Hz filter in the Orion rings.
> 
> With the SDR during CQWW I tuned in on 2 DX stations
> that were 50 Hz apart when I centered them at 350Hz in
> the passband.  In other words when I first had one
> station at 350 and then tuned the other to 350 I had
> moved frequency by 50Hz.  One station was in the south
> Caribbean and the other was in eastern Europe.  There
> were American stations and European stations calling
> both.  So at any given time there was 3 to 6 stations
> on freq calling.  I was on 80 M and I have good omni
> directional DX antennas.  The stations were about s4
> and the calling stations were as high as 20 over.  I
> was able to take either station down to single signal
> levels with the SDR, and I was able to work both
> stations in succession with no trouble.  
> 
> I brought up the Orion on the same freq and was not
> able to separate the signals or the calling stations
> no matter how I adjusted the controls, using the same
> antenna switched over to the Orion.  There is no
> ringing in the SDR at any filter or DSP setting.  At
> 25 and 10 Hz both noise and offending signals outside
> the passband disappear.  At 10 Hz bandwidth, centered
> on a -73 dBm carrier, I found the filter has a
> bandwidth of 33 Hz at -130dBm, beyond 33 Hz I was no
> longer able to discern the s9 signal. No radio I have
> ever used has this kind of performance.

I'd have separated those signals by ear or my outboard DSP. The
condition I was talking about is where the signal is alone, but just at
a level below the noise where I'm not sure its real or I'm imagining
that signal, not one moving the S-meter. I heard N0UK on 2m that way
last night and the audio DSP didn't help copy (in fact its narrower
noise bandwidth may have hurt in ear processing). But switching in the
mechanical filter in the IF did help that negative signal to noise ratio
making that signal copyable. 

My Timewave DSP has a noise reduction mode which does reduce noise and
make a really weak signal a bit more copyable, but only if the signal
was audible in the noise to begin with. It won't enhance signals that
are down to that imagination level. But the IF filter in the 857 does
help those weak signals.
> 
> 73 W9OY