Just a couple of points.
In the K3(S) there is no "RF Gain" control unless by RF gain you mean "It's not
the audio gain gain control."
The "RF" gain control operates on the i-f amplifier, which is after the analog
noise blanker. In this regard, it is little different from AGC, which operates
on exactly the same circuitry. Why some people believe that they are better at
controlling i-f gain than the AGC system does is beyond me, but old wife's tales
die hard. If this is hard to fathom, watch the S meter as you reduce "RF"
gain. The reading increases, no different from letting the AGC do it.
Attenuation is a different matter. It operates at RF and is a viable tool.
About noise blanking, I think I had a little to say about that almost 40 years
ago: http://k6mhe.com/n7ws/Noise_Blanker.pdf
Wes N7WS
On 9/3/2017 1:48 PM, Bob McGraw K4TAX wrote:
Depending the type of noise, for repetitive pulse type noise only, the Noise
Blanker does it job. Now one must understand that all pulse noise is not
alike. Therefore, different values of NB, both with the IF values and with
DSP values, will require some adjustments. If the noise is not repetitive
then the NB is not the better choice but the NR is the better choice. Again,
depending on they type of noise, certain combinations of NR values will be
necessary.
Yes, that is correct in that the Noise Reduction function is not available or
can not be activated in the DATA mode. However the Noise Blanker can be used
in the DATA mode. Again, the Noise Blanker is for repetitive pulse type noise.
I've spoken with many hams and find their understanding of Noise Reduction
being described as often does not work as expected. Further discussion seems
to indicate they want NE........Noise Elimination. Well, NR........Noise
Reduction does in fact work when the values are selected based on the type of
broad noise spectrum being encountered. NR has very little effect on pulse
type noise.
One fact not clearly understood, is that most hams operate with too much RF
Gain. Thus the correct application of ATTENUATION and RF Gain reduction will
greatly improve receiver performance in the face of noise.
Optimizing receiver gain compared to band noise and the noise floor of the
receiver is explained in a quote from Rob Sherwood, Sherwood Engineering:
"If receiver noise floor is 10 dB below band noise, the receiver is
contributing less than 0.5 dB of the total noise.
Band noise varies by band over 30 dB, 160-10 meters. It also varies by
direction and time of day, plus what the sun is doing. In an noisy urban
environment it is anybody's guess as to your band noise level.
A simple test is to see how much the noise coming out your speaker increases
when you switch between a dummy load and your antenna, when tuned to a dead
spot on the band.
Example on 10 meters at my rural QTH, IC-756 Pro III: preamp OFF, noise goes
up 3 dB. That means the receiver is contributing half the noise. Preamp 1 ON,
band noise goes up 9.5 dB. Almost all legacy receivers are designed for 10
meters, and attenuation is desirable on the low HF bands."
In Rob's first statement, how do we get the band noise to be 10 dB above
receiver noise? Use Attenuation and RF Gain reduction. As an example, if
receiver noise floor is -130 dBm and the band noise, no signal, is S-5 or -97
dBm, the difference being 33 dB. This would then indicate one should employ 15
dB of Attenuation and 8 dB of RF Gain reduction. Or 10 dB of Attenuation and
some 13 dB of RF Gain reduction. Of course the band noise will be comprised
of different noise components, depending on band and many other factors as he
suggests.
73
Bob, K4TAX
On 9/3/2017 3:06 PM, Keith Onishi wrote:
In my experience, NR is much better than NB against power line noise.
However, NR does not work on DATA mode. I use BHI Compact In-line DSP Noise
Eliminating Module, which is inserted between K3 line out and USB audio module.
For effectively eliminating noise, tuning RF gain and AGC level in addition
to NB and/or NR would give you better results.
de JH3SIF, Keith
2017/09/04 4:38、Wes Stewart <wes_n...@triconet.org> のメール：
I agree. The adjustments are far too many and arcane. I'm currently plagued
with powerline noise that has yet to be fixed, although they are supposed to
be working on it. The K3S blanker is slightly better than useless. When I
set it aggressive enough to be audibly useful, FT8 decodes multiple signals
at 120 Hz intervals, which upsets sequencing.
I'm finding that my SDR-IQ that I normally use only as a bandscope, has
better noise blanking on its demodulated audio than the K3. Too bad I can't
use it with WSJT-X.
I suspect, but do not know for sure, (maybe the designer can enlighten us)
that there is insufficient delay in the (analog) signal path and the noise
gets through before blanking takes place.
Wes N7WS
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