I wonder if one reason we do not seem to have a common thread of what NR or
NB does or does not do is the following :
My comments are based on the 565
Orion with 1.372 and just recently 2.054.
Using the MAIN receiver , the bandwidth of the signals or noise or
whatever is limited by whatever roofing filter is in use after the first
mixer and the 15 khz filter at the LPF feeding the DSP A to D.
If filters are set as AUTO then it will be whatever BW you have
set with the BW control. If you set the roofing filter manually in
the FILTER manual you can keep the bandwidth of the noise
slot at 20 , 6 ,2.4 or whatever.
I had noticed that on much (but not all) of my noise , the
NB function in the sub receiver was much more effective than in
the main receiver IF I had the FILTER BW set to AUTO .
If I went into FILTER and kept the roofing at either 6 khz or 20
khz , then there was essentially no difference between the two NB.
Looking at the 565 Orion block diagram I have for the two receivers , the
roofing filter in MAIN rx limits the BW of signals+noise to the 450 khz band
pass filter (15 kHz wide) just before the DSP A to D LPF converter.
IN the SUB rx , The bandwidth of the
signals+noise is 20 KHZ after the first mixer and set at 15 khz by the
450 khz band pass filter just before the SUB rx A to D converter LPF .
For me this explains the NB differences I have seen and I suspect
it has significant influence on how NR functions.
Now to NR - I cannot offer much there , other that just
personal observations - no data. I have spent far more time
with the noise blankers both DSP and Hardware.
it seemed I could play with BW and PBT and filter taps and do
as well or better than the NR. I will say that in 2.054 with very narrow
bandwidths (100 to 200 cycles) which is all I ever use because of
my noises and interference - I catch myself with it ON far more often
than I ever did in 1.372 and it seems
to help but as someone else said - its is even more critical tuning than
the 100 cycles requires - seems like if I am off more than 20 cycles or so
the signal does not "pop out of the noise".
As an aside - I have some form of swept interference from a cable system
next door (which looks like a touch lamp spectrum) but is on the cable drops
that is S9+40db from about 3570 to 3590 or so (on worst night sweeps from
3570 to 3720) and is still S9+20 or so on 40 at 2F , etc - thank goodness I
dont work much SSB as it is still potent even on 20 m. BUT with the front
end opened up and the NB on , I can actually copy S4 CW signals in that
mess - they are modulated at the rep rate of the sweep BUT I can copy them
!!! With the front end on AUTO I cannot even detect the cw signals in there.
FWIW -- de Hank K7HP
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