On 4/7/19 10:37 PM, Peter Monta wrote:
Does NIST publish the transmitter bandwidth? I've never seen it, but I
haven't done a serious search.
Maybe somebody near enough to get a clean signal could measure it. What
does a spectrogram look like?
Some of the KiwiSDR receivers are close enough to get an excellent signal.
Coincidentally I gave this very experiment a try some weeks back; give me a
few days to find the recordings and analysis scripts. But the bottom line
is that 100 microseconds seems possible. The antenna bandwidth is some
hundreds of Hz, if I remember right, but the high resolution would come
from tracking a specific point on the amplitude trailing edge (say, the 90%
point).
The precision of measurement isn't so much related to only the bandwidth
of the signal as to the combination of bandwidth, integration time, and
SNR.
THe trick is knowing what the "decorrelation time" of the channel is,
because that sets an upper bound on integration time. And, of course,
the phase noise of the transmitter and receiver.
In any case, extracting microsecond timing from a 1 kHz BW signal is
straightforward (assuming sufficient SNR, etc.)
As an extreme example, we measure timing of the round trip radio signal
to Jupiter and back with an accuracy of 1E-15 (5 picoseconds). The
signal is very narrow band (<<1 Hz), but we do integrate for 1000
seconds. And we use other means to disambiguate things like "which
cycle" are we on.
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