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HAMSAT Polarization Posted by PE1RAH, 4 July'05:Hi AMSATs,
The Indian Space Research Organisation (ISRO) has
informed me that the best way to work HAMSAT is with
linear antennas.
ISRO who made the satellite has designed the HAMSAT
with circular up and downlink.
With the use of linear antennas the loss with be
always 3dB, even with polarization changes due to
faraday rotation.
When the ground station uses circular polarization the
losses will be in the order of 0 to 20dB.
0 dB when polarization is same, and up to 20dB when
polarization changes totally.
When using circular polarization the groundstation
need to be able to change between RHCP and LHCP.
Because this is not in the power of most hams, a
linear antenna is a very good option.
It will give only a 3dB loss over a more high-tech
switcheable station.
With the high level downlink signals, and the
sensitive uplink the 3dB loss should be not a problem
at all.
Just enjoy HAMSAT, as I enjoyed to develop on of its
transponders :o)
73
William
PE1RAH
HAMSAT Polarization Posted by PE1RAH, 1 July'05: *Hi AMSATs,
This morning I received the answer from ISRO about my
question for the uplink polarization, and why they
used LHCP on the downlink.
The uplink of HAMSAT is in RHCP, opposite of the 2m
downlink that is in LHCP.
I was also supprized to hear that the downlink is in
LHCP, as most amateur sats use RHCP.
The reason that ISRO used RHCP and LHCP is to avoid
interaction between the uplink and downlink signals.
By using opposite polarizations the output of the
satellite would less interact on its 70cm input.
Personaly I think the antennas are at such close range
that this will not really help...
At least we know the right polarizations, and the
reason why it is done.
Myself I have fixed RHCP antennas, and actually have
had never any problems with the HAMSAT.
On the other hand the signals are that strong that it
should be no problem, and most of the hams I hear on
HAMSAT are in aligator mode and can use some
polarization attenuation on the uplink :o)
73
William
PE1RAH
HAMSAT Polarization Posted by PE1RAH, 30 June '05:
Hi AMSATs,
I was away for a few days and arrived back home
yesterday. When I checked my email I see an answer
from ISRO on my question to confirm the polarization.
I think I remembered that it was said to be RHCP, but
this is wrong...
ISRO confirmed in the email to me that the downlink of
HAMSAT is LHCP. They advise to use linear antennas to
avoid fluctiations in downlink signal level due to
polarization changes. The downlink is strong enough to
overcome the 3dB losses you have with a linear antenna
to an circular antenna.
About the uplink they didn't mention. I request them
also to confirm about the downlink polarization.
When I get the answer I will post it...
73
William
PE1RAH
HAMSAT telemetry, Posted by William, 25 May'05
Hi,
The HAMSAT gives only telemetry to the ISRO groundstation on none ham
frequencies.
ISRO use it to check the status and to switch on/off the transponders and
change attitude when needed.
The telemetry will only be activated by ISRO groundstation and is not for
public use.
The frequencies are secret and only for ISRO.
73 pe1rah
William HAMSAT launch, posted by PE1RAH, 5May'05 Hi AMSATs around the world,
I am just back from a 2.5hr drive from Shriharikota
launch place.
There I witness the launch of the PSLV-C6 with with
the naked-eye at 5km distance and the launch went
successfull for all 100% :o)
All four rocket stages ignited and seperated as
planned, and without any deviation from the predicted
plan. It was very interresting to see how my radio
finally went into space. It is the best hamradio
experience I ever done in my life.
The latest news I have is that the onboard computer
showed that the batteries and solar panels work
normal. HAMSAT is spinning at 1.5RPM and will be
increased to 4RPM. When this is done the main
transponder will be switched on, and a few days later
the Dutch transponder will be switched on.
We just are a few days away from "CQ CQ HAMSAT" qso's.
When HAMSAT is released for ham use, the ISRO will
open a webpage and publish the actual data and
keplers.
This will be known to the world...
Tommorrow morning I leave to Bangalore where is the
ISRO groundstation. There I will wait to hear the
first signals from my radio...
I hope HAMSAT will work okay and for long time, so it
can be in service for the world-wide ham community.
I am looking forward to any report from you...
73,
William Leijenaar
PE1RAH ,with my radio in space now :o)
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