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Mike,<br>
In regard to your need for a receiver that will demodulate signals
< 200Ksymbols, The DATV-Express group makes a tuner/receiver that
will receive a DVB-S/S2 signal as low as 70Ksymbols/sec on a
frequency of 144 to 2420MHz. I designed the hardware part of it and
sell it for $75 + shipping. Check out the specs at
<a class="moz-txt-link-abbreviated" href="http://www.DATV-Express.com">www.DATV-Express.com</a>. Let me know if I can help.<br>
Regards,<br>
Art Towslee<br>
WA8RMC<br>
<br>
<div class="moz-cite-prefix">On 12/8/2019 8:05 PM, Mike Parker via
Ground-Station wrote:<br>
</div>
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A team headed by the University of Arizona is working on a 6-U
satellite that will fly at 500 km altitude. The satellite, named
CatSat after the UofA wildcat mascot, was described in a paper
presented at the Amsat Annual Meeting. We are shooting for a
launch that could be as early as one year from now. The plan is
to have a downlink using DVB-S2 modulation generated by an FPGA on
the AstroSDR card provided by Rincon Research. This modulation
was chosen so that hams that have been working phase4 ground
DVB-S2X might receive and demodulate the link. We are planning to
transmit a limited number of ModCod’s. Modcod 7, QPSK 3/4, and
modcod 17, 8-PSK 9/10 are likely choices.
<div class=""><br class="">
<div class="">Two experiments plan to use DVB-S2 modulation on
the downlink. One involves transmitting high quality video,
and the other will capture and retransmit narrowband pieces of
the HF ham bands containing WSPR and FT8 signals. Closing the
link to our 6.1 meter diameter ground station is no problem,
and we are planning on a modulation bandwidth up to 20 MHz and
bit rates over 50 Mbps when using the satellite’s inflatable
directive antenna provided by FreeFall. But closing the link
to a ham 0.6 meter dish when operating with an
onmi-directional transmit antenna poses a very different
problem. We will likely require small downlink bandwidths on
the order of 200 kHz.</div>
<div class=""><br class="">
</div>
<div class="">We are looking for a demodulator to assist in
testing the satellite, and also a demodulator for use in the
ground station. So we are reaching out to you for
suggestions. We hope that an available commercially for an
affordable price, or perhaps something designed by a member of
this group. We have neither the desire or time to reinvent
the wheel.</div>
<div class="">Several things concern us we would appreciate
advice on.</div>
<div class="">1) We read with interest a paper by Downey, Evans,
and Tollis, “DVB-S2 Experiment over NASA’s Space Network”. It
said “ typical commercial DVB-S2 receivers are not designed
for symbol rates below 300 kbaud”. That is consistent with
our observation that many commercial demodulators do not seem
to have a lowest bandwidth specification. Anyone know of one
that goes lower in bandwidth while having a high bandwidth
capability?</div>
<div class="">2) We need to have a demodulator that will output
raw DVB-S2 frames, bypassing any transport layer protocols
which are normally used with DVB-s2 such as Multi-protocol
Encapsulation(MPE) or Geeric Stream Encapsulation (GSE).
Downey, Evans, and Tollis used a Newtec MDM6000 modem. Is
there a better or cheaper solution? (I haven’t priced one
yet).</div>
</div>
<div class="">3) Doppler shifts are also a concern, especially at
a low data rate, but we have a plan to solve that if necessary
using a local oscillator in the ground station that is swept
according to ephemeris predictions to de-Doppler the signal
before demodulation.</div>
<div class=""><br class="">
</div>
<div class="">Oh yes, some good news. The first of our 6.1 meter
dishes has been reassembled in Rincon’s parking lot in
Centennial, CO. A picture with assembly in progress is
attached. I’m flying up tomorrow with a 10 GHz feed horn and
LNA to see if we can hear signals!</div>
<div class="">Mike Parker, KT7D</div>
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