[TenTec] Orion II NR Performance Measurements

[Lin Davis]

Hi Grant,

Just a thought- I assume you made these measurements with a steady state signal. 
Well that will be the worst case for a downward expanding type of NR.

However, if the carrier was modulated (like in Sinisa test with continuous 
dits), and the RF gain adjusted so that the difference between the signal plus 
noise level and the noise level with no signal is maximized, the average SNNR 
would be at it's best (by definition). Seems to me, this test is more 
applicable; more "real-world".

Wouldn't that be a better test? Let me know what you think.

Almost forgot-I'm assuming a narrow bandwidth, since you have shown quite nicely 
that, by itself, the v2.xxxx NR doesn't do much in this regard.

Lin

Grant Youngman wrote:
>>>BW=500Hz:  SNNR degrades by approx 2dB with  NR=9.
>>
>>Degrades?...strange  result!  This
>>implies a noise bandwidth of ~800 Hz.   Simply
>>turning DSP BW to 100 (which has an actual BW of 150 Hz) 
>>should  **improve** S/N by 5.2 dB.
> 
> 
> Let me clarify a point here.
> 
> What you say is true.  However, that isn't exactly what I was looking at.  
> 
> The absolute value of SNNR does in fact increase, with NR off, and the
> bandwidth narrowed as it should  But the numbers I gave were the DIFFERENCES
> between SNNR with NR off and SNNR with NR=9.  
> 
> That says that (at the 500HZ bandwidth for example), while the absolute SNNR
> increased with narrowed bandwidth and NR off, the "improvement" by turning
> on NR was negative.  I don't know why that happens, just that it does.  It
> may be distortion products as Buck suggested.
> 
> In any case, I've been arguing all along that the only valid figure of merit
> for any NR system is how it changes SNNR, not whether or not the radio
> becomes "quiet".  At least to my own satisfaction, I don't believe the new
> algorithm is doing much relative to that figure of merit.  With the signals
> set to be under (as far as I can tell anyway) the AGC threshold, it is true
> that when NR is turned on the radio gets quiet.  Unfortunately, the signal
> level decreases right along with the noise level.  So I normalized
> everything to the value of the signal peak, with and without NR.  In that
> case, and with a relatively weak signal -- (S+N) set to provide a 3dB
> increase over (N) with no NR as measured on a 3400A True RMS meter -- this
> very small change up or down is SNNR is what NR seems to be providing.
> 
> Grant/NQ5T
> 
> 
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