I have one little nit to pick with this. In a properly designed blanker,
there is no requirement that the noise be repetitive; blanking should occur on a
single pulse or on random pulses. Blanking becomes ineffective when 1) an
undesired signal appears in the detection bandwidth that exceeds the threshold
and triggers the blanker more or less continuously or 2) the duration of the
noise pulse is so long that intelligibility suffers. Atmospherics fall into this
latter category.
See: http://k6mhe.com/n7ws/Noise_Blanker.pdf for more of my opinion on this.
(The missing text in the last paragraph was not my fault.)
Actually now that I think about it, I have another nit. Although the control on
the K3 front panel says "RF Gain", which I guess differentiates it from AF Gain,
it really should say "IF Gain". It has absolutely nothing to do with affecting
the gain ahead of the i-f amplifier. Front end attenuation can affect noise
power into preamp and/or the first mixer (and noise blanker circuit); "RF Gain"
cannot. In fact RF Gain is applied first to exactly the same point as AGC, the
post-filter FET. The FET can't tell the difference, which might be news to the
guys who turn off the AGC and "ride the RF gain control."
Wes N7WS
On 6/13/2019 6:09 AM, Bob McGraw K4TAX wrote:
The Noise Blanker only affects repetitive pulse noise such as ignition type
noise. Lightning and atmospheric is random noise. As to the Noise Reduction,
I find that use of the Attenuation and RF Gain control is far superior to
using DSP systems. Also remember it is Noise Reduction and not noise
elimination as many seem would like to believe. If one realized 6 dB of noise
reduction using the system that's good. At the same time, any noise
reduction system will add distortion to a SSB or CW signal.
From very authoritative source, the optimum receiver performance configuration
is to have the no signal band noise about 10 dB above the noise floor of the
receiver. Since we can't change the noise floor of the receiver, the option
is to change the incoming level of the noise as presented to the receiver
input. The K3S receiver noise floor is about -135 dBM. If one has a no
signal band noise of S-5 or -97 dBm, the difference is 38 dB. This says we
need 28 dB of Attenuation and RF Gain reduction. That would be 15 dB of
Attenuation and about 2 S units of RF Gain reduction or 10 dB of Attenuation
and about 3 S units of RF Gain reduction. This in no way changes the
sensitivity of the receiver nor does it impede the ability to hear weak
signals. Unfortunately many hams belie that more gain is needed to hear weak
signals. With receivers of 50+ years ago often the receiver noise exceeded
the band noise. That however is not true with today's modern receivers.
As to using the Noise Reduction, I do not use it at all for SSB and for CW.
If I do use it I find F1 and a value of 1 to 3 about all I'm willing to
accept. Of course the type and magnitude of the noise does require different
settings.
If I use the Noise Blanker I find it necessary to first set the IF NB to OFF.
Then adjust the DSP through its values to get what seems to be the best
result. Remember the value. Then set the DSP NB to OFF. Then to the IF
noise adjustment and find what seems to be the best result. Leave it at that
and then back to the DSP Noise blanker and set it to the previous obtained
value. This optimized them individually. I've not been successful in
trying to adjust both at the same time. And remember it only works on
repetitive noise such as ignition noise or line noise and not random
atmospheric noise.
The receiver gain method works best. Hope this helps.
73
Bob, K4TAX
On 6/13/2019 6:43 AM, Nr4c wrote:
This is not an easy thing.
First, are you hearing general band noise, a constant “ shhhhhhhhhhhh” or
pulses as in lightning, power line, or ignition type noise.
For band noise, the NR will be your best solution. Experiment, but don’t go
too deep. Deep settings will distort and make it sound like you’re underwater.
For the pulse noises, try IF first, again don’t use extreme settings. If this
doesn’t work, try the DSP settings and see if this will work.
I have NB set to Med4. NR is set to F1-3.
YMMV.
Have fun!
Sent from my iPhone
...nr4c. bill
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