Long ago I did some WWVB signal-to-noise measurements with an HP 3586C selective voltmeter (commonly used by the FMT-nuts). I measured the signal power at 60.0 kHz with 20 Hz bandwidth. Then I measured the power a small offset plus and minus (100 Hz? I don't recall), and took the mean of the two to get the noise power. I used a voltage-probe antenna.
Since all readings were taken with the same bandwidth I didn't bother normalizing to 1 Hz, and just used the dBm difference between the signal and mean noise as the result. I took measurements every 5 minutes or so to capture the 24 hour cycle of SNR. John On May 6, 2018, 1:09 PM, at 1:09 PM, Charles Steinmetz <csteinm...@yandex.com> wrote: >Hal wrote: > >> I assume the problem is noise. Is there any simple way to measure >the noise >> around 60 KHz? How about not so simple? >> >> Extra credit for a way that others nuts can reproduce so we can >compare the >> noise at my location with other locations. > >For any location near a city, the noise level (QRM and QRN -- mostly >the >former unless there is storm activity within a few hundred km) is >shockingly high. High enough to be clearly seen and measured with a >good spectrum analyzer. So the *simplest* way (but not necessarily the > >cheapest, depending on what is in your lab already) is to use a good >spec an with noise integration over the band of interest (e.g., HP >3585A >or B). You get noise density readings in volts per root Hz. Divide by > >the antenna length and you have volts per root Hz per meter. > >Lacking a suitable spec an, any receiver with a reasonably narrow rx >B/W >and a calibrated, input-referred detector can be used. Wave analyzers >(frequency-selectable voltmeters, e.g., HP 3586) are good candidates, >as >are some commercial receivers with calibrated "S" meters (e.g., Ten-Tec > >RX340). It would also be pretty easy to design a simple "sniffer"-type > >receiver (input op-amp, active filter, logarithmic detector feeding a >standard 1mA meter movement) that could be calibrated by design from >first principles and that everyone interested could build for, perhaps, > >$25-30. > >In the suburbs of a fairly large US city with aerial electric service, >I >generally see noise densities measured in tens to hundreds of uV per >root Hz per meter below 100kHz. In other, similar locations I have >seen >as much as hundreds of mV or more per root Hz per meter. It depends on > >local factors (whether the electric service is buried or aerial, how >well the power utility maintains its equipment, how far away the >nearest >industrial neighborhood is, how far between dwellings, how much noisy >technology the neighbors use, etc, etc.). > >In order to compare with others, everyone needs to use the same >antenna. > There are lots of possibilities, but for the sake of universality I >recommend a 1m vertical whip. Everyone can make one of those. > >Note that this sort of antenna is NOT the best type to minimize >received >noise and maximize received S/N ratio. For that, you generally want a >balanced, shielded loop. > >Best regards, > >Charles > > >_______________________________________________ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.