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RE: UO36's 38k4 Downlink!

Just to clarify this....  The downlink on 437.025MHz is on 38k4 and is only
on while in view of the groundstation at this stage.  This may change soon,
but we are still power limited at the moment.  This downlink is transmitting
~10W into a quadrifilar antenna.

The 437.400MHz downlink is on permanently using 9600BPS.  The downlink is on
~3W and the antenna is not optimised for the nadir pointing attitude.

The 437.025MHz downlink will ultimately be switched to 437.400MHz and the
9600 downlink on this frequency will be switched off.  So, if you're making
a 38k4 system and need to crystal something up, the 437.400MHz is the
UoSAT-12 frequency.

Chris G7UPN

-----Original Message-----
From: Peter Guelzow [mailto:pg@tasma.aball.de]
Sent: 23 May 1999 13:49
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] UO36's 38k4 Downlink!

38k4 reception of UOSAT-12 OSCAR-36

UO-36 is transmitting on 437.025 MHz with 38400 baud. Usually this
downlink is operational in addition to the 9k6 downlink on 437.400 MHz,
when the spacecraft is in sunlight or in range of the command station in
Surrey. Since I almost share the same footprint, I was able to 'grab' a
couple of thumbnails and a few hires images over the last week. 

I use an TNC31S with 38k4 g3ruh modem and SYMEK's TRX4S highspeed data
transceiver with excellent performance. The TRX4S is capable of 153k6
using an 300 kHz Filter. My version uses an 110 kHz filter, which is
still fine for 76k8 operation and also works great at 38k4. Indeed, no
doppler correction is needed. The TNC31S was modified to support 9k6
uplink while receiving at 38k4. For 9k6 Uplink on 2m I use my old

UO-36 70cm downlink is pretty strong from it's quadrifilar antennas and 10W
output power, but since the TRX4S was originally designed for terrestrial
use, it's necessary to have a preamplifier for better receiving. 

I can grab even large files without any missing packet. I get about 1.5 MB
data per pass, depending on how actively Surrey is downloading pictures.
Downloading these many and large image files at 9600 baud is nearly
hopeless and I'm even looking forward to see the downlink running at
76.8 Kbaud.  :)

Colin Hurst, VK5HI is currently modifying his CCD Display software
to also support the UO-36 format. The Thumbnails can already be displayed
after renaming the UTxxxxx.imt files into TMxxxxx.imt files and loading
them into CCD Display by clicking on them in the Explorer. Some of the
.imi files can also be displayed partially.
We may expect a newer version from Colin, when he gets all the necessary
picture format information and enough time to develop this software, so
please be patient with him.

English written information about the TRX4S can be found here:

Best wishes
 Peter, DB2OS

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