I wasn't clear on this point: You don't need any new firmware to try the experiment. Just use K3 Utility to temporarily alter the bandwidth of the 6-kHz filter as explained in the setup instructions below.
In fact, you don't really even need K3 Utility. You can change the filter bandwidth using the CONFIG:FLx BW menu entry, where 'x' is the number assigned to your 6-kHz filter. Wayne N6KR On Feb 3, 2016, at 7:03 PM, Wayne Burdick <[email protected]> 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
