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satellite passbands

P

Philip Newman

Jan 1, 1970
0
I would like a definition on what is meant by satellite passbands in reagard
to communication systems

thanks,

Phil
 
A

Anthony Fremont

Jan 1, 1970
0
Philip said:
I would like a definition on what is meant by satellite passbands in
reagard to communication systems

Allot of satellites contain linear transponders. These are basically
wide banded frequency convertors, they listen on one band of frequencies
and retransmit on another offset from the listening frequency by a fixed
amount. Usually the input frequency is in a different RF band than the
output. Low earth orbit satellites travel so fast (with respect to the
surface of the Earth) that doppler shift is a big problem. Rather than
trying to adjust transmit frequency to account for the doppler, the
transponder is wide enough to allow for some drift due to doppler.

One amateur radio satellite that I used to talk thru listened on 2mtr
VHF and transmitted back on 10mtr HF. The transponder was about 20khz
wide IIRC. This allowed several SSB conversations to occur
simultaneously without interference to one another.

michael brown
 
P

Philip Newman

Jan 1, 1970
0
thanks. another question that has cropped up, are the definitions for
x-band, c-band etc

what are the frequency ranges for these? is there any difference for UK or
US? I am in the UK so those would be preferable, so far I have:
X-band: 520GHz
S-Band: ?
D-Band: 660-692GHz
C-Band: 430-510GHz

thanks

Phil
 
R

Rene Tschaggelar

Jan 1, 1970
0
Philip said:
thanks. another question that has cropped up, are the definitions for
x-band, c-band etc

what are the frequency ranges for these? is there any difference for
UK or US? I am in the UK so those would be preferable, so far I have:
X-band: 520GHz
S-Band: ?
D-Band: 660-692GHz
C-Band: 430-510GHz

I'd assume these definitions to be global.
AFAIK, the
S Band is 2.5 GHz,
X Band is at 10GHz,
Q Band is at 35GHz
W Band is at 90GHz

Rene
 
J

Joe McElvenney

Jan 1, 1970
0
Hi,

Take a look at this -

http://www.packer.dsl.pipex.com/images/
radar_band_designations.gif

Don't forget to string it all together. This won't give you
the exact band edges but will give you the general idea. I once
read the reason behind the use of these particular letters but
can't now remember what it was.


Cheers - Joe
 
K

Ken Taylor

Jan 1, 1970
0
Anthony Fremont said:
Allot of satellites contain linear transponders. These are basically
wide banded frequency convertors, they listen on one band of frequencies
and retransmit on another offset from the listening frequency by a fixed
amount. Usually the input frequency is in a different RF band than the
output. Low earth orbit satellites travel so fast (with respect to the
surface of the Earth) that doppler shift is a big problem. Rather than
trying to adjust transmit frequency to account for the doppler, the
transponder is wide enough to allow for some drift due to doppler.

One amateur radio satellite that I used to talk thru listened on 2mtr
VHF and transmitted back on 10mtr HF. The transponder was about 20khz
wide IIRC. This allowed several SSB conversations to occur
simultaneously without interference to one another.

michael brown
Hmmm, a satellite doesn't have a wide passband to get around Doppler shift -
in the case of simple satellites, the Doppler is ignored because, as you
say, there's enough room for all (or because interference can be tolerated).
Passband is broad so as to allow for the number of carriers to be
transported. Also, a highly inclined geostationary satellite can exhibit
significant Doppler shift which requires correction if the bandwidth of the
carrier is low enough that the Doppler shift is significant wrt it.


Ken
 
A

Anthony Fremont

Jan 1, 1970
0
Ken said:
Hmmm, a satellite doesn't have a wide passband to get around Doppler
shift - in the case of simple satellites, the Doppler is ignored
because, as you say, there's enough room for all (or because
interference can be tolerated). Passband is broad so as to allow for
the number of carriers to be transported. Also, a highly inclined
geostationary satellite can exhibit significant Doppler shift which
requires correction if the bandwidth of the carrier is low enough
that the Doppler shift is significant wrt it.

If a LEO satellite contained a repeater listening on a specific
channelized frequency, it would be nearly impossible to use without some
kind of computerized compensation at the transceiver tweaking the
transmit and receive frequencies accordingly. The passband eliminates
some of this fuss, until you run off the end of the passband anyway. ;-)

I'm curious as to how a stationary satellite might experience
significant doppler shift problems. With virtually no relative motion
to the land based station, how could it happen? Now with a LEO at
1000km altitude traveling at >30,000 km/h, doppler is significant and
constantly changing. You can't really ignore that. ;-)

I made allot of QSO's on RS-10/11 before it croaked. It really took
some practice to be able to communicate with someone effectively,
especially when a good pass was good for less than 15 minutes of talk
time. It's kinda ironic that most of the QSO's were with a friend of
mine that only lived about 2 miles from me. It's a real hoot though the
first time you actually hear your voice coming back delayed. ;-)

michael
 
K

Ken Taylor

Jan 1, 1970
0
Anthony Fremont said:
If a LEO satellite contained a repeater listening on a specific
channelized frequency, it would be nearly impossible to use without some
kind of computerized compensation at the transceiver tweaking the
transmit and receive frequencies accordingly. The passband eliminates
some of this fuss, until you run off the end of the passband anyway. ;-)

I'm curious as to how a stationary satellite might experience
significant doppler shift problems. With virtually no relative motion
to the land based station, how could it happen? Now with a LEO at
1000km altitude traveling at >30,000 km/h, doppler is significant and
constantly changing. You can't really ignore that. ;-)
'Geostationary' is a relative term - they are not 'stationary'. The amount
of drift in the orbit varies - some of the Inmarsat satellites (which I work
with) have several degrees of inclination, which can cause several kHz of
Doppler drift. With small (<~10kHz) carriers, this is very significant. The
corrections are done in the ground stations (as ditinct from the consumer
end of the link).
I made allot of QSO's on RS-10/11 before it croaked. It really took
some practice to be able to communicate with someone effectively,
especially when a good pass was good for less than 15 minutes of talk
time. It's kinda ironic that most of the QSO's were with a friend of
mine that only lived about 2 miles from me. It's a real hoot though the
first time you actually hear your voice coming back delayed. ;-)

I only tried on AmSat a few times - I heard myself coming through a few
times, but never had a QSO. :)

Cheers.

Ken
 
A

Anthony Fremont

Jan 1, 1970
0
Ken said:
'Geostationary' is a relative term - they are not 'stationary'. The
amount of drift in the orbit varies - some of the Inmarsat satellites
(which I work with) have several degrees of inclination, which can
cause several kHz of Doppler drift. With small (<~10kHz) carriers,
this is very significant. The corrections are done in the ground
stations (as ditinct from the consumer end of the link).

OK I knew that the "stationary" satellites moved around a bit, but what
I didn't know was that carriers in the khz range were used on
satellites.
I only tried on AmSat a few times - I heard myself coming through a
few times, but never had a QSO. :)

Which satellites did you do it on? I never really messed with the ones
that required 440 transmit ability or circularly polarized antennas. My
amsat setups were quite crude as I lived in an apartment at the time.
;-) The Russian RS satellites were the only ones I played with, but
they were a blast. You had to really stay on top of things to make sure
you didn't lose the other guy as the doppler was really pronounced.

Satellites and chasing weather balloons (google on south texas BLT's)
before they all started carrying GPS, were probably the most fun I've
had in amateur radio. Of course working russians while only running
five watts into a 300' high kite antenna is pretty neat too. ;-)
WARNING: don't try this at home, I'm not responsible for others idiotic
behavior, only my own. ;-D
 
K

Ken Taylor

Jan 1, 1970
0
Anthony Fremont said:
OK I knew that the "stationary" satellites moved around a bit, but what
I didn't know was that carriers in the khz range were used on
satellites.


Which satellites did you do it on? I never really messed with the ones
that required 440 transmit ability or circularly polarized antennas. My
amsat setups were quite crude as I lived in an apartment at the time.
;-) The Russian RS satellites were the only ones I played with, but
they were a blast. You had to really stay on top of things to make sure
you didn't lose the other guy as the doppler was really pronounced.

Crikey! I *think* it was one of the Russki ones, but it was mid-eighties, so
my memory isn't too flash on the subject. I could hear myself whistling
through it despite just whip antennas at 440 and 144. One of my mates was
driving through a valley in a fairly remote part of Australia and could hear
the beacon for the satellite clear as a bell as he drove through, but once
he came out of the valley it faded into the noise. Lots of nice effects out
there! :)
Satellites and chasing weather balloons (google on south texas BLT's)
before they all started carrying GPS, were probably the most fun I've
had in amateur radio. Of course working russians while only running
five watts into a 300' high kite antenna is pretty neat too. ;-)
WARNING: don't try this at home, I'm not responsible for others idiotic
behavior, only my own. ;-D
LOL! That was something we always wanted to do, but the Air Force used our
area as a low-altitude training area for many years after getting F111's, so
it was out of the question.

Cheers.

Ken
 
M

Michael A. Terrell

Jan 1, 1970
0
Joe said:
I once
read the reason behind the use of these particular letters but
can't now remember what it was.

Cheers - Joe

The letters were assigned out of sequence for military usage so the
enemy would have a harder time figuring out what was going on. Of
course, this was in tube days when even UHF was difficult to use
reliably. Only key people knew what the operating frequencies were, and
you didn't have good LNAs, accurate frequency counters, or a microwave
spectrum analyzer you could carry aboard an airplane to look for the
Enemy's radio signals. The early military HF and VHF radios used regen
and super regen receivers that emitted enough noise they could be
tracked by the enemy. The poor quality also allowed the use of
broadband jammers to wipe out an entire range of signals to keep the
enemy from talking to other units.
 
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