[TenTec] Bavarian Contest Club / Orion Review

[Grant Youngman]

> So DSP makes the noise? If you hear (excessive) noise in the receiver
> with its antenna disconnected or shorted, it is internally generated
> noise by the RX stages. It would mask very weak signals and this 
would
> explain the K6SE "weak signal test" poor results. Blaming DSP is lame
> excuse. 

I'm not "blaming" DSP, and did not say that DSP "makes the noise".  
What I said was that the noise you hear in the audio output when there is 
no (meaning no antenna) signal is an "artifact" of the AGC controlled 
digital IF.  And that, is not an excuse, lame or otherwise.

The "gain" through the DSP IF stages is very high, when THRESHOLD is 
low and there are no signals present.  You can see what happens 
yourself if you adjust THRESHOLD up.  The noise will decrease 
significantly because the DSP IF gain/compression point changes.  I think 
this has also been described in the manual, in the discussion of weak 
signal optimization, the effects of NR on THRESHOLD, etc.

Seems to me we've got to stop thinking of the digital AGC controlled IF 
stages as just a digital version of an analog IF.   It behaves differently.  
Do I know enough about the specifics of the DSP algorithms to tell you 
precisely why?  No.  Does it?  Most certainly.

I'll repeat it again, because there is nothing I've observed to alter my 
conclusion -- the "noise" you hear when there's no antenna connected is 
not indicative of high front end noise in the Orion.  There is absolutely no 
evidence I'm aware of that bears out that conclusion, and others who 
have done quite a bit of testing seem to find no issues with weak signal 
performance when there is actually a signal source.

As for K6SE's tests, I said what I had to say .. way too much .. :-)  about 
those a long time ago,  and my view of their validity has not changed -- 
particularly in light of what all of us have learned about optimizing weak 
signal performance in the Orion since that fiasco.

Grant/NQ5T