[Ground-station] Need advice on DVB-S2 modem

[Art Towslee]

Mike,
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 www.DATV-Express.com. Let me know if I 
can help.
Regards,
Art Towslee
WA8RMC

On 12/8/2019 8:05 PM, Mike Parker via Ground-Station wrote:
> 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.
>
> 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.
>
> 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.
> Several things concern us we would appreciate advice on.
> 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?
> 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).
> 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.
>
> 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!
> Mike Parker, KT7D
> image001.jpg

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