Hello Guy, Thank You for an interesting analyse. Which s/w and f/w do You have on K3 loaded please?
73 - Petr, OK1RP On Sat, Dec 14, 2013, at 05:35 AM, Guy Olinger K2AV wrote: > This may be specific to a K3 and no joy for other rigs. But there might > be > parallels elsewhere. Definitely YMMV. > > Usually in a 160 contest I try and get a run frequency down around > 1815-20. > For some reason in my locality that range is, and for a long time has > been, > a general garbage minimum in the noise floor around here, sometimes 2-3 > dB > better, so there is no incentive to CQ elsewhere. I have not had a > problem > establishing down around 1815-20, even when running 100 watts. > > But this year, off and on since late summer, and of course without any > rhyme or reason or published schedule, I have had a really bad > intermittent > power line style buzz that was S7 to ten over S9, depending on only > heaven > knows what. I have not had any luck localizing it, largely because of > it's > variable and erratic nature. A lot of the time it has irregularly > separated > fast bursts, almost like it's trying to send Morse with its buzz. > > On the first night of the ARRL 160 contest, buzz was entirely absent. And > I > actually had the ARRL 160 weekend clear of family conflict for the first > time in recent memory. Oh Joy! By the end of the first night I already > had > a personal best for the contest. The second night the noise struck half > way > through with a solid buzz. Ten over S9 in my usual hangout 1815-20-ish. A > little less noise up higher but still covering all but the louder > signals. > No real help using my newly repaired and pattern-verified NE RX antenna. > Loud there, too. Earlier work had ruled out a source in my or neighbor's > houses. No quickie fixies. > > I was unable to hear anything except the louder signals, which I had > pretty > well worked out the previous day. Forget operating. So I decided to > experiment with the noise mitigation methods/settings on the K3. > > Usually in these buzz circumstances, you can't find a persistent weak > signal on 160 far enough into the noise to let you experiment with noise > mitigation settings based on signal to noise. You wind up using the > reduced > noise level as the only clue for settings. > > Reduced noise level method is fine if you are working strong signals and > you just don't want to hear the noise. But to pull out weak signals what > you really need is to restore signal to noise separation all the way down > to the weak signals. It turns out best signal-to-noise and best > level-of-noise do not always generate the same weak signal readability. > Some methods/settings reduce noise well but also trash the weak signals > in > the process. > > But being the contest, 160 was *loaded* with weak signals to test with. > So > I spent a few hours experimenting with K3 settings on weak signals, > optimizing for S/N. Came up with NB only (no NR) DSP T1-7 + IF NAR4 using > "250" 8 pole filter, which clearly gave the best separation between weak > signal and noise, without the usual weak signal obliteration from > traditional noise blanking in a contest. > > Usually the buzz gating the NB will add a 180 Hz raspy modulation (center > carrier and +180, -180), an irritating buzzy noise, and can mush the > wanted > signal. Narrowing the CW width to 250 or 200 Hz (+/- 100 Hz) cleans off > both the modulation (3 x 60 Hz), and signal-covering "hashy fuzz" caused > by > the irregular shape of the buzz waveform. > > After the determination of those settings, I scanned the band with those > settings in NB. I discovered a narrow "null" in the noise or sweet spot > between 1831 and 1833, sounding almost normal, with clear rendition of > weak > signals, which was up to 2 s-units better than the NB improvement in the > least effective spots, which included my normal hangout of 1815-20. > Don't > ask me how that works, because I haven't a clue. > > 1831.5 was unoccupied, as was 1832.5 in a later stretch, where operating > with the blanking on, it was as if the noise was not there at all. (See > an > earlier post about my unfortunate adventure with the DX window rule.) > > That narrow sweet spot in the blanked noise was still there Tuesday, at > 1830-1832. With the noise back solid, and using the NB settings above, > Tuesday night I was hearing LZ2DF on 1832 clearly, at what I would call > 559 > or 549. He was not hearing me running 1.5 kW, so this was clearly a > normal > state of affairs, controlling noise was on his end, not mine, even though > the buzz was full on. > > Wednesday the buzz was there with separated bursts, but not quite so > loud, > and the aforementioned NB settings killed it at least semi-decently > across > the band. Go figure. I was able to clearly pull out way-down birdies and > such, simply not there without the NB. > > Thursday the noise-blanking sweet spot was at 1.838, and a little broader > than during the contest. The RX antenna clearly hears a weak birdie at > 1.838 much stronger than on the TX. Yes, Virginia, the RX antenna has > been > working correctly the whole time. > > Today the buzz is gone at my noon-time opportunity for driving around and > trying again to locate it with my K2. > > Tonight the buzz is back, mostly steady. The sweet spot is at 1.828 > tonight. > > We will be renewing the search for the noise when it decides to come back > steady in the daytime. > > But regardless, now I have noise blanker settings for the Stew and CQ 160 > which actually do improve signal to noise for weak signals in power line > noise -- just in case the noise is still with us. And I know now to look > for the wandering-around sweet spots where the K3 does some real magic, > before I go for a run frequency. > > 73, Guy > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
