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AMSAT: 38K4



From: "Stacey E. Mills, M.D." <w4sm@cstone.net>
Subject: [amsat-bb] 38k4 baud satellites
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If you're tired of the "slow" 9k6 baud sats, now may be a good time to look
into what it takes to go to the 38k4 downlinks.  At least two of the
current satellites, TO-31 and UO-36 have this capability.  P3D's RUDAK has
multiple high speed modems and is likely to be very active at 38k4, as
well.  Several of us have been working with Chris Jackson to tweak WISP to
function best with these new satellites, and I believe that they (at least
UO-36) will be widely available soon.  Even now UO-36 is often transmitting
at 38k4 baud over the US (437.025) during daylight hours.

The uplink on these satellites is 9k6 baud, so if you're active on
UO22/KO25, etc., no changes are needed on the transmit side.  However, the
extreme bandwidth of the downlink at 38k4 necessitates some receiver
changes as all of the current ham rigs are too narrow banded to handle
this.  There is very good, relatively inexpensive solution, however.  Symek
(www.symek.com), a German company in Stuttgart, makes a small
receiver/demodulator board that intercepts the data stream from your
transceiver's IF.  These IFD boards cost DEM 235 (about $122).  They come
with excellent installation instructions (in English if appropriate) and
are available for most of the major satellite transceivers and receivers
used by amateurs.  If you don't see your rig listed, drop them a note and
they'll work with you to get you an IFD board.  I ordered using a credit
card over the internet and my modules were received in a few days.  I've
installed one in a Yaesu FT-736R and another in a Kenwood TS-790A.  The
Yaesu installation is very simple and the Kenwood is only a little more
involved.  Anyone comfortable making the 9k6 baud modifications should
easily be able to handle this.  Importantly, normal function of the radio
is not affected.

With regard to a modem that will handle 38k4 downlinks, there may be
several options.  I've been told that a standard G3RUH 9k6 FSK modem can be
adapted to run at this speed.  There's also been discussion that a
DSP56002EVM board is capable (just) of running at this rate and some
software may be available for this modem on the TAPR web site. I have not
pursued either of these solutions, so I can't comment further.

Symek has two very high speed modems (up to 614K baud!) that work extremely
well.  One is a two port version (TNC3S) and the other, less expensive one
is single port (TNC31S).  These can be ordered from the factory in any
specified configuration.  I have the less expensive TNC31S.  Mine is set up
to wake up in KISS mode with 38k4 downlink, 9k6 uplink, and a 57k6 PC
connection.

The downlink at 38k4 on UO-36 is really spectacular! Watching the byte
counter fly by is quite a treat. Efficiencies of 90-100% are easily
obtained with directional antennas and a preamp.  Doppler tuning is not
really necessary on the widebanded 435 Mhz downlink.  Downloads of 1.5 Megs
are possible on single passes, and all three components of a color image
can be captured in short order.  I used to think 9k6 was fast, at least
compared to 1k2 on AO-16, now when I look at KO-25/UO-22, the byte counter
seems to be moving in slow motion!

To me at least, this high speed (internet level) transfer rate, and the
ability to grab images on a single pass, really brings some excitement back
to the digital sats.

STANDARD DISCLAIMER:  I am not an employee of Symek and I receive no
compensation from them... just a very satisfied customer wanting to spread
the word.

Hope to see you in the queue(s) soon.


--
 ________________________________________________________________________
 Stacey E. Mills, W4SM    WWW:  http://www.cstone.net/~w4sm/ham1.html
   Charlottesville, VA    PGP key:      http://www.cstone.net/~w4sm/key
	
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