[time-nuts] WWVB: measuring local 60 KHz noise

[John Ackermann N8UR]

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 <csteinmetz at 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
>
>
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