[time-nuts] GPS outage? 19:00-2100 UTC Tue

Bill Byrom time at radio.sent.com
Thu Aug 20 02:35:56 EDT 2015

The term "BNM" also initially confused me. It appears to be "Broadcast
Notice to Mariner", a report produced by the US Coast Guard with
important warnings for ship navigation.

Detecting GPS interference is an interesting topic. I work as an RF
Application Engineer for Tektronix, so I'm biased about this topic.
Different types of interference will show up in different manners on
various types of spectrum analyzers. I would use a directional antenna
with low noise preamplifier with a Real-Time Spectrum Analyzer (RTSA
like the low cost Tektronix RSA306 USB 3 analyzer) so you can see the
statistics of signals at or below the thermal noise floor. The jamming
signal might be wideband Gaussian noise, band-filtered Gaussian noise,
BPSK or QPSK or QAM modulated signals, frequency chirped signals, or
other RF signals people might come up with to create interference. I'm
purposely not going to suggest which of these would be better or worse
at interfering, but a RTSA can see weak signals near the thermal noise
floor which might be unintentionally or purposefully causing

Some people assume you can't use a spectrum analyzer to see the GPS
constellation from a good GPS amplified antenna because each GPS
received satellite signal is over 10 dB below the thermal noise floor
and a normal received GPS constellation is still below the kTB thermal
noise floor (-174 dBm/Hz). But the uncorrelated combination of a typical
GPS constellation with an antenna at a good location will sum with the
background noise and will be sufficient to push the noise floor up maybe
0.5 dB (depending on how many satellites can be seen) above the thermal
noise floor, and this is easy to see if you use 10,000 or more
averages/sec using a RTSA or a bitmap statistical display. Again, I'm
not trying to advertise anything in this forum but just give you a
technical answer to your question.

Bill Byrom N5BB
On Thu, Aug 20, 2015, at 12:12 AM, Hal Murray wrote:
> What's the BNM column on that chart?
> What sort of gear would I need to detect a local jammer?

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