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
to communication systems
thanks,
Phil
Philip said:I would like a definition on what is meant by satellite passbands in
reagard to communication systems
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
Hmmm, a satellite doesn't have a wide passband to get around Doppler shift -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
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.
'Geostationary' is a relative term - they are not 'stationary'. The amountAnthony 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. ;-)
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. ;-)
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).
I only tried on AmSat a few times - I heard myself coming through a
few times, but never had a QSO.
no_one said:here is one source of definitions
http://www.jneuhaus.com/fccindex/letter.html
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.
LOL! That was something we always wanted to do, but the Air Force used ourSatellites 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
Joe said:I once
read the reason behind the use of these particular letters but
can't now remember what it was.
Cheers - Joe