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JT65 is a slow protocol for propagation reports. In short it takes 60
seconds to send 13 characters. Then you wait 60 seconds for a reply,
and repeat.
The 60 seconds are actually 1 second silence, 46.872 second of signal,
then another 12.128 seconds of silence, allowing for clock drifts and
for a human to choose the reply.
The mode is this slow in order to add a lot of redundancy and to make
it easier for the receiver to dig out a signal way below the noise
floor. It was originally meant for making contacts by bouncing
signals off the moon, which has a path loss of ~250dB. Someone even
managed a JT65 moonbounce on 10 Watts using JT65 with gear you and I
could
buy/build!. That’s
the power of a low energy light bulb!
I wanted to do propagation experiments with SDR, with low power in
various frequency bands, but couldn’t find a GNURadio module for
JT65. So I made
one.
The JT65 specification is very well written,
except for the parts it says “the code is the specification”. Which
would normally be fine, but the code is in Fortran and Fortran is
terrible.
JT65A is Continue reading