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 For software/hardware reviews see: http://www.nk7z.net For MixW support see: https://groups.yahoo.com/neo/groups/mixw/info For SSTV help see: http://groups.yahoo.com/neo/groups/MM-SSTV/info 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 > > > > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to d...@nk7z.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
