[Elecraft] K3/K3S noise blanker performance greatly enhanced (at my QTH) -- need testers

Fri Feb 5 12:57:45 EST 2016

Hi Wayne,

On list report as you asked for...

Set up as described, only using a 13KHz filter in F1 position...  

Using a florescent light, which makes a rather ugly wide band noise,
only on 18 MHz., I performed a sort of blind test....  

After doing the full setup as you described on a very weak CW station,
I hit the NB button as fast as I could for several seconds while
looking away from the radio...  This confused me as to if it was on or
off...

I then while still looking away from the radio brought the NB on and
off line, and stopped on teh CW that was easiest to copy.  

I did this five times, and after each test, I re-scrambled my memory by
again, hitting the NB switch many times, and looking away from the
radio.  

Five out of five times the NB was off when I stopped, indicating that
the NB made the CW harder to copy.  

Sorry...  I will try later tonight, when all the Horticultural lights
come on line on 40 meters, which has tons of RFI from them.  I will
report again...

-- 
73's, and thanks,
Dave

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On Wed, 2016-02-03 at 19:03 -0800, Wayne Burdick wrote:
> Hi all,
> 
> If you have...
> 
> - really ugly noise sources that neither of the K3/K3S noise blankers
> completely clean up, and 
> 
> - a 6-kHz crystal filter, and
> 
> - a narrow crystal filter (200-1000 Hz)
> 
> ...then you may want to try an experimental technique I've been using
> the past couple of days. In many cases it produces dramatically
> improved blanking, at least in narrow-band modes (CW, PSK, FSK). I've
> been able to hear many weak signals that I simply couldn't hear
> before.
> 
> It may also work for SSB signals in conjunction with a 15-kHz crystal
> filter, but I haven't tried that yet.
> 
> The kind of noise I'm talking about is often quite unstable, with a
> buzzy sound, possibly drifting around a bit in frequency and
> amplitude. Light dimmers, switching power supplies, and various other
> devices create such noise. The noise may be narrowband: as you tune
> the VFO, you may find there's a "hump" of noise that's anywhere from
> 2 kHz to 50 kHz wide. It may also have very complex waveform with
> multiple noise pulses back-to-back in a burst. 
> 
> These types of noise are difficult to deal with. The IF blanker's
> signal path may be too wide (0.2 to 2 MHz), resulting in too little
> energy in-band to trigger the gating signal. The DSP blanker's RF
> signal path may be too narrow, making it hard for the DSP to
> distinguish noise from desired signal.
> 
> * * *
> 
> Setup:
> 
> 1. Connect the radio to a computer running K3 Utility. Go into the
> Configuration / Configure Crystal Filter setup screen.
> 
> 2. Find your 6-kHz filter (probably FL1 or FL2). Now the fun part:
> fake out the firmware by entering a bandwidth for this filter that's
> just 50 Hz wider than your narrow CW filter (ideally 250-500 Hz). *Do
> not* change the filter offset. But *do* make sure that the 6-kHz
> filter's CW and DATA enable boxes are checked.
> 
> 3. Click "OK" to save this experimental crystal filter configuration
> setup. 
> 
> 4. You will now find that when the WIDTH control is rotated from,
> say, 0.40 to 0.45, the XFIL selection will jump from something like
> FL4 directly to FL1 or FL2 (your 6-kHz filter). That, hopefully, is
> the boundary where magic may occur, below.
> 
> * * *
> 
> The Experiment:
> 
> 1. Find one of your most offensive local noise sources. I have them
> on most low bands. The stronger the amplitude the better. Narrowband
> sources may provide the most dramatic results.
> 
> 2. Back down the AF gain control, then *turn off AGC*. You may need
> to use the RF gain to keep the signal from clipping. 
> 
> NOTE: The reason for doing this test without AGC is to make sure you
> can hear the full effect of applied noise reduction. AGC flattens out
> the receiver's audio response, making it hard to compare different
> settings. (If you find that the noise-remediation trick works, you
> can later turn AGC back on, and while the effect won't be as obvious,
> any benefit in signal-to-noise ratio will still apply.)
> 
> 3. Select CW mode and adjust the WIDTH control for your narrow
> filter's bandwidth (example: "BW 0.40"). 
> 
> 4. Turn on the noise blanker (tap NB) and hold NB (LEVEL) to access
> the blanker parameters. 
> 
> 5. Set the IF blanker to OFF (VFO B). Then experiment with the DSP
> blanker settings (VFO A) to obtain the best possible reduction in
> signal.
> 
> 6. While still the LEVEL parameters are still displayed, adjust the
> WIDTH control to the next step up (example: "BW 0.45"). This should
> kick in the 6-kHz filter, *but the DSP bandwidth and filter graphic
> will still show a narrow passband*. In other words, you're widening
> out the crystal filter but making very little change in the DSP's
> internal filter bandwidth (15 kHz IF, and AF).
> 
> 7. Now re-optimize the DSP noise blanker settings for the 6-kHz
> filter case. Did the noise drop? (If you have a signal generator,
> e.g. an Elecraft XG3, you might put an antenna on it and generate a
> weak signal right in the middle of the noise to get more definitive
> results.)
> 
> 8. Try it on other noise sources. It may help on some but not others,
> due to the wide variance in noise signals.
> 
> Please log your results and report them to the list, at least until
> Eric shuts down the thread :)
> 
> * * *
> 
> IMPORTANT:
> 
> As you can imagine, opening up the crystal filter bandwidth much
> wider than the DSP bandwidth will make the receiver more susceptible
> to in-band interference. If necessary, use RF GAIN, preeamp, and
> attenuator settings to reduce all interfering signals to a manageable
> level.
> 
> I find there are many occasions on which better blanking is really
> critical, even if gain must be reduced in order to take advantage of
> it. 
> 
> * * *
> 
> If we get enough positive responses from this experiment, we'll
> provide a simply, intuitive way of selecting the 6-kHz filter for
> noise blanking purposes. And maybe the 15 kHz filter for SSB use, if
> applicable. For example, we might add more selections to the DSP
> blanker parameter (presently t1-1 to 3-7). Suggestions welcome.
> 
> 73,
> Wayne
> N6KR
> 
> 
> 
> 
> 
> 
> 
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