Hi K9YC, Many thanks for the detailed analysis.
1. Sorry, I do not understand why u said, quoted, "Gauging by the FT8 signals centered around 7075 kHz, I'd call this QTH pretty noisy". This is the FT8 band at 7074kHz, usb and wsjt-x decoded good copy of traffic. Those are wanted ft8 signals. Ft8 Traffic was busy, 4 decodes per 15 seconds cycle. Strongest signal is 4 dB snr. Most are better than -4dB snr, rare one was weakest at -19 dB. >From call sign, many are from Indonisia, Australia and new zealand, 4000km from Hong Kong sota qth. So, it was good received signal from 4000 to 6000km away. It was healthy signals. 2. The sota site has no AC utility electricity and no street lamps, it is a laws protected country park area where they preserve nature. 100 meters away is a public toilet with solar panel and pir triggered led lighting, which should be off as there is likely no one in toilet. Solar panel was zero output as it was dark, 30 minutes after sunset. No charging pwm noise. 500 meters away, and blocked by hill profile, as 100 meter lower, is a ranger office. Should be all person off duty at that time. Sure, there may be some smps still running. Up 150 meters, are two airport long range survilance radars, one primary, one secondary radar, with Powerful smps inside. Radar range about 700km for the hong kong fir, flight information region, from hong kong to taiwan to philpines. There is a residential estate, 500 homes, 30 floors buildings, 2 km away, with all kind of smps inside, computer, fluroresent lighting, led lighting, vfd motor drive for lift, etc. 3. Yes, the reguar stable cw lines are from the notebook computer. 73 Simon On Saturday, December 29, 2018, Jim Brown <[email protected]> wrote: > Hello Simon, > > The straight vertical lines in the waterfall are harmonics of a stable > clock, perhaps your computer. The "wavy" vertical trace around 7054 looks > like the noise from a mains-powered noise source like a switch-mode power > supply or variable-speed motor controller -- the clue is that it is not > stable in frequency. In both of the power-related sources, the mains > voltage is rectified, minimally filtered, then chopped to produce square > waves in the range of 10-20 kHz. For the SMPS, the waveshape and frequency > is more or less constant (but unstable, so it drifts on startup), while for > the motor controller, is varied to control motor speed. Both of these > sources are heard as "growley" carriers. Both of these sources are normally > surrounded by noise, which is heard as random. In this plot, I see another > source at about 7058. > > This trash is usually coupled to wiring connected to the source as a > common mode signal, and that wiring acts as a transmitting antenna. It is > not uncommon to hear this stuff several miles from a very strong source. > > Gauging by the FT8 signals centered around 7075 kHz, I'd call this QTH > pretty noisy. I don't see anything in the waterfall that looks like CW. > > Spectral and waterfall plots like this are an excellent tool for studying > noise. One change I'd suggest though is that the vertical scale be expanded > so that the strongest traces fill the spectrum plot. For this particular > trace, I'd suggest an upper limit of about -100 dBm. > > You might find my RFI tutorial useful in thinking about this. > http://k9yc.com/KillingReceiveNoise.pdf Also, NK7Z has a lot of great > RFI stuff on his website, including a large collection of spectral and > waterfall plots of known sources. > > 73, Jim K9YC > > On 12/28/2018 9:22 AM, Simon wrote: > >> This is an outdoor SOTA receive-only test to evaluate FT8 weak signal >> performance. >> >> I have near zero HF experience. Is this considered as 'very good' LOW >> noise area? -130dBm noise floor on 7074kHz. >> >> Hope it is not too off topic for the list. >> >> It is a 500 meter hill, protected by country park laws, prohibited >> residential building and no people live there. >> >> They also have airport long range radar and HF ship to shore receiving >> station in that area (on next nearby hill peaks). May be, the area is >> chosen as 'low noise area'? >> >> Test with >> >> SDRPlay RSP1A >> Thin Long wire, quarter wavelength at 7MHz, 40m band, just 1 meters >> above ground, for simple first test. >> >> Time 1040Z, 1840 local time. Just shortly after Sun set. >> >> Noise floor is -130dBm on SDRUno softwre. >> >> The strongest 7074MHz FT8 signal is -100dBm. I got 3 to 4 decodes per >> 15 seconds cycle. On WSJT-X Ver 2.0, SNR ranges from +4dB to -20dB, >> from station 4000km away from Hong Kong. Including Indonisia, >> Australia, New Zealand and Japan. >> >> 73 >> >> Simon >> >> >> >> _______________________________________________ >> wsjt-devel mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/wsjt-devel >> >> > > > _______________________________________________ > wsjt-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/wsjt-devel >
_______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
