On 24/01/2019 11:00, N1BUG wrote:
On 1/24/19 5:41 AM, Bill Somerville wrote:
On the new lower LF bands a decoder can take advantage of the far more
stable propagation than is found on the higher short-wave bands.
Coherence across significant periods of time allows assumptions that
frequency and phase of a signal are essential stable, this opens up
significant techniques for improved sensitivity.
Hi Bill,
Forgive me if this is a silly question, but does that imply extreme
frequency stability would be required of the transmitter and
receiver? I hope this won't be a mode limited to those who have
everything GPSDO referenced. WSPR-15 seems reasonably drift tolerant.
73,
Paul N1BUG
Hi Paul,
not a silly question at all. I doubt frequency accuracy will be an
issue. OTOH frequency stability certainly is relevant, you can only take
advantage of the stability of the propagation path if the transmitted
signal is at least as stable. Drift can be accounted for if it proves to
be a serious problem, the first order drift component is likely to be
the most significant by far, for crystal controlled sources, once
frequency references have reached temperature equilibrium. WSPR like
modes have an advantage that considerable CPU resources can be used to
process the received signals since, unlike QSO modes, there are no
deadlines to decide the next message content based on message context so
elaborate and expensive algorithms to make such corrections are feasible.
I am fairly confident that given a mode that might have the sensitivity
of WSPR-15, on LF bands, with similar or less bandwidth and similar T/R
period to WSPR-2, users would consider upgrading their transmitters for
the necessary frequency stability.
73
Bill
G4WJS.
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