I am these days reading the conference proceedings EME 2016, and of course
all of them need a quite reading and some of them are far from my knowledge.
When I came across with WSJT-X from Joe, I found its new feature named
"automatic Doppler tracking" I was happy that I found implemented that
When I was starting in EME, I come from SATs world, I wrote the bellow
question into moon-net (more than 3 years ago) and nobody answered me
giving some kind of support, all the emails were in the direction that I
should listen on my echo as all people did through the years in CW mode.
Now Joe base your new feature in the "constant frequency on the moon". At
that time I named "The frequency we hit the moon".
Congratulations Joe, one more time you do things easy to us.
De: Juan Antonio Fernandez [mailto:email@example.com]
Enviado el: sábado, 04 de mayo de 2013 14:45
Asunto: Doppler question
Sri I made, at least a mistake, I send it again.
Very interesting answers. I come from Sats world, where the Doppler is a
serious issue and it is so quick that it is impossible to work JT65.
I will speak thinking in one carrier. Sats need to receive in only one fix
frequency (it is an active RX with a wideband), if the Sat receives a
carrier in this frequency then it will be repeated. The signal TX from the
Sat will be in one fix frequency. So people who work Sats must correct its
TX frequency (according with actual
Doppler) to reach the sat in its fix frequency, in the same way because of
the Sats will repeat this signal in a fix frequency, people must correct its
RX frequency (according with actual Doppler).
This way of dealing with Doppler is very interesting because NOBODY KNOWS
the Doppler of the other stations and nobody needs to know it, we only need
to know our own Doppler.
If we would use this agreement to EME communications we will always speak
about the frequency we hit the Moon, in other words the frequency which the
Moon hear us and repeat our signal.
The actual EME software shows us the Doppler as the sum of the Doppler
effects to reach the Moon and to receive the bounce signal, so Moon will
receive us at ½ Doppler announced, the other ½ effect will appear after de
I will try to set a couple of examples.
1.- We will agree to hit the Moon in 1296.070. This is the frequency I will
announce in the log. In our software the dates will be:
The sign that the software shows will aplly to RX frequency and the opposite
to the TX frequency, and always ½ magnitude on each one.
Both of us must deal with Doppler, each one must do their task to hit the
moon in the agreed frequency and to receive the bounce according our
Doppler. Then we must set on our transceivers:
TX: 1296.070 -1.5KHz = 1296.0685MHz
RX: 1296.070 +1.5KHz= 1296.0715MHz
TX: 1296.070 +1.0KHz = 1299.071MHz
RX: 1296.070 -1.0KHz= 1296.069MHz
Each station who sees the post will act only according its own Doppler.
Don´t mind where is the DX station.
2.- In this case I see a signal in my receiver in 1296.070. What kind of
pair of frequencies I must set (I know nothing about the DX station I have
still decode nothing), I only know me own Doppler, and it is +2KHz. I must
hit the moon in the same frequency that my
TX: 1296.070 -1.0KHz = 1296.069MHz
RX: 1296.070 = 1296.070MHz
WE WILL NOT NEED TO KNOW NO MORE THAN OUR DATES.
I haven´t spoken about what frequencies will be the echoes (both echoes), to
make the understanding easy.
As a drawback we should change our habits, we should always use the RIT as
TX: The frequency we choose plus the opposite sign of Doppler and ½ Doppler
RIT: the sign of our Doppler and ½ Doppler magnitude.
Although at first glance it seems not to be interesting in 144MHz but we
will always hit the target in whatever band, even in 144MHz.
Somebody can tell that they need a computer, to do JT65 of course, if you do
CW surely have a smart phone with the proper software to know your own
Doppler or you can print it before.
If I made some mistakes let me know.
It is my 2 cents.
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