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
|