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

Charles Steinmetz csteinmetz at yandex.com
Sun May 6 13:08:57 EDT 2018


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





More information about the time-nuts mailing list