On 30/04/2019 16:54, Mark Spencer wrote:
Hi:
I am planning on experimenting with JT9A on 50 MHz. I am curious, are the
frequency stability requirements for the various slow modes (including JT9)
reasonably proportional to the tone spacing ?
Given the tone spacing for JT9A of 1.736 Hz, would a goal of one 1 Hz frequency
stability be reasonable, excessive or inadequate ? (I realize in addition to
any frequency drift from my equipment the drift from the radio at the other end
of the link and any Doppler shift introduced by the propagation mode will also
be relevant.)
Thanks in advance for any comments.
73
Mark Spencer
VE7AFZ
[email protected]
Hi Mark,
some of the decoders have an element of AFC that allows them to track
linear frequency drift up to a certain threshold, I don't believe the
slow JT9 decoder is one of them. Because of that you will need a
frequency stability that keeps all the tone symbols of a message within
their expected frequency bins, i.e. the drift per message should be less
than the detection bandwidth. The JT9 signal is spectrally dense so the
detection bandwidth is roughly equal to the tone spacing.
In summary, a net drift overall (yours plus your QSO partner's plus
Doppler if you are moving relative to each other or using a moving
reflector) of 1 Hz per minute is good enough but might start to impact
sensitivity as signal energy starts to bleed away from the decoder's
capture range. Aircraft scatter is unlikely to work.
73
Bill
G4WJS.
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