[ICOM] Pro 3 noise reductiion

[Adam Farson]

Hi Jeff,

Reports of distortion when using NR have come up before on the IC-756Pro3
reflector. In several of these cases,  as I recall, a defective DSP Unit was
involved.

I observed a significant NR improvement in my Pro3 as compared to the Pro2.
This is described here:

http://www.qsl.net/ab4oj/icom/ic756pro3/pro3notes.html

Normally, I leave the NR pot at 50% (12 o'clock) in SSB mode, with AGC MID.
It knocks down the band noise by about 20 dB, but does cut the treble
response somewhat as is to be expected. It increases the SNR noticeably, and
can make the difference between copying and not copying a weak SSB signal.
Increasing the setting above 50% does not reduce the noise level further,
but does not cause distortion.

In CW mode, the NR will be less effective as the noise bandwidth is much
less than in SSB, and the NR algorithm has less noise power to work with. I
find that with NR at 50%, there is a noticeable noise reduction with the 1.2
kHz filter, less with the 500 Hz filter and none to speak of with the 250 Hz
filter. Again, this is to be expected (N = kTB). During the test I
conducted, AGC = FAST.

I did not observe distortion of the CW signal at any NR setting, even with
the IF bandwidth reduced to 50 Hz via Twin PBT. On the rare occasions when I
operate CW, the NR control stays at 50%. I was listening to CW signals
varying in level between S0 and S5.

Your Pro3 may have a faulty DSP Unit. I would suggest that you contact the
Icom service centre.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Jeff Frank
Sent: 13 August 2005 10:40
To: icom at mailman.qth.net
Subject: [ICOM] Pro 3 noise reductiion

I'm having a hard time finding any use for the noise reduction control on my
Pro 3.  It's not helpful to me under practically any conditions when I'm on
cw and I'm not crazy about it's usefulness on ssb. One of the reasons I
bought the Pro 3 was because the noise reduction was supposed to be improved
over the Pro 2. The earliest product reviews on e-ham.net include reports on
how much improved the NR is, and how happy people are with it. I never had a
Pro 2 so I can't say anything about the comparison. Maybe I'm not using it
correctly or maybe there's a problem with my rig. I find that unless a cw
signal is relatively strong (s-5 or better) the NR control distorts the
signal and makes it rough sounding and HARDER to copy. If the signal is
weak, near the noise, using the NR distorts it into unreadability and I can
copy it better without the NR. And if the signal is stronger, I don't need
the noise reduction anyway. If I keep the NR setting below about 9:00, it
does make a little positive difference but I don't feel overall it's doing
very much. I don't operate much ssb, but when I have used it, it just seems
to take the highs out of whatever noise there is, and I could do that with
any decent audio filter. I would be very interested in hearing what other
people's experience with the NR on the Pro 3 is so I can try and make an
educated guess as to whether or not there is anything wrong with mine. If
anyone is getting good results with theirs, please let me know what your
settings are and under what kind of band conditions. And if anyone had the
Pro 2 before the Pro 3 I'd sure like to hear how the Pro 3 NR is an
improvement over the older model.  Thanks very much.

Jeff KX2P


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