Hi Spence,
the fact that you have to use different frequencies when
transmitting and receiving is quite simply the Doppler principle. It
also has nothing to do with linear.
Of course, these two frequencies are different, mirroring each other
around the frequency of the Greencube.
The aim must be to feed the satellite's QRG. When receiving, you
have to adjust in one direction; when transmitting, it's the other
way round.
Only if the satellite is directly above you or if its movement path
is exactly at a 90° angle to you, then both frequencies are
identical (in my case 435.308400 MHz).
73, Tom, DJ6TB
Am 21.10.2023 um 12:03 schrieb Spence
M0STO via groups.io:
toggle quoted message
Show quoted text
Hi Tom,
? ? ? ? ? ? ?I am totally confused on this matter as I have
spoken to a well known source that tells me if the transponder
is linear then the uplink and downlink frequencies are the same
on a Digipeater satellite on the same band. As GC is 435.310mhz
then transmitting (assuming the correct Doppler is employed)
whatever the RX frequency is then the TX should be the same?
? Now I dispute this as I’ve tried RX and TX without split
and I’ve never had a single packet received or an ACK from GC.
If the other spice is correct then it should send packets that
are received from me without issue. Either GC has some kind of
audio band pass filter (I always use 1500hz as my CF) or
something else is afoot here.?
? Re: sub-VFO. Yes you’re correct and after much research I
found that the sub VFO cannot be adjusted with CAT commands,
there was never a provision for it.
? Now my mind is really scrambled because every program I’ve
used eg: HRD, PSTrotator, Sat-PC32 all try to implement Doppler
shift for RX and TX on different frequencies. For example, if
the satellite is just over the horizon on 435.313mhz RX then the
TX is set at 435.307mhz and all programs follow this trend, non
seem to think that the satellite is linear and thus should be on
the same frequencies. As the satellite comes close the RX moves
close to 435.310mhz on RX and that same for TX with RX going
down in frequency and TX going up in frequency. When the
satellite is overhead at say 90 degrees the RX and TX should be
both at 435.310mhz and then when it’s going away from me the RX
goes down past 435.310mhz towards 435.307mhz and the TX goes up
to towards 435.313mhz and eventually the satellite disappears
beyond the horizon.
? I don’t claim to be an expert in satellite and until GC
came along I had never worked a DigiPeater satellite so this has
been a steep learning curve for me. I have worked VK from the UK
using 6700 delay and successfully made a 10,700 mile QSO of
sorts.?
? Using my FT991A which does allow Sub-VFO changes via CAT I
can work GC easily and have many USA and Japanese contacts (of
course Europe too) with little effort and the Doppler was set
and the Downlink frequency was 435.312mhz and Uplink 435.308mhz.
So that sort of debunks the totally linear idea unless GC has a
really wide audio passband.?
? Again, satellite is very new to me and I’m trying to get my
head around it as the physics say up and down are the same on a
same frequency DigiPeater, however, GC seems to defy this
convention and I’m curious why?
?Sorry to burned the group with this but I’ve looked hard
into resolving g this but I just get conflicting information.
The kindest regards,
De Spence M0STO?
Sent while portable! please excuse typos.
?
Hi Spence,
I am working the GC since 6 month and I did not find a
solution for that problem so long
So I drive the main vfo by gpredict (via cat) and adjust
the sub-vfo manually by those values gpredict shows in the
TX-qrg window.
I think the FT-847 has no option to adjust sub-vfo in
split mode on the same band.
There are videos on youtube which show hints by using
satpc-32. But you have to trigger rx/tx/rx/tx manually and
so you (normally) miss the reception of your own
transmission digipeated by the satellite.
73, Tom, DJ6TB
Am 01.10.2023 um 23:49 schrieb
Spence M0STO via groups.io:
?
Dear group,
? ? ? ? ? ? ? ? ? ? ?Perhaps if I explain a little
background and what I’ve tried it may help to prevent
things I’ve done being repeated.
GreenCube is my problem! Working GreenCube is a
nightmare because of one reason, it’s a satellite and
it’s also a digipeater.
? Every program I’ve tried will happily tune the
main VFO but will not change the sub VFO. PSTrotator,
HRD etc. OmniRig does not seem to like to change the
sub VFO while it’s tuning the main VFO.?
? The FT847 has a major drawback though. In
satellite mode split mode this is achieved easily
because the bands are V/U or U/V uplink and downlink
and full duplex but GreenCube sits on the same
frequency (bar Doppler correction). So the radio will
“error” when trying to TX on the same band, that’s
common knowledge.?
? The issue is when in split mode (the only real
way to work GreenCube and Doppler shift), as above,
all software shows the VFO change in software but not
on the radio. I’ve had extensive conversations with
Codrut (PSTrotator) and after many adjustments to his
software he can’t manage to get the sub VFO to alter
with the main VFO. The nearest I’ve been to achieving
this was in HRD and setting the Uplink and Downlink
manually but as above only the “main” downlink VFO
would alter.
? I know that some versions of the FT847 had some
issues with asynchronous communications but this
wouldn’t affect the communication when altering the
frequency.?
? I plan to inspect the bit data and see if sub-VFO
commands are actually being sent. I’ve successfully
sent manual commands to turn on sat mode, LSB/USB
mode, enter frequencies etc.?
? I wonder if anyone has any thoughts on this?
