[Namaste-dev] Re: DVB-S downlink format

Bob McGwier rwmcgwier at gmail.com
Tue Jul 15 15:05:15 PDT 2008


Please forgive my having missed this.  It was a little hectic around July 1.

;-).

There is nothing that prevents us from using any standard so long as it is
not covered by protections (patents, etc.) that prevent us from implementing
it openly, using it openly, and so long as it is not deemed by the FCC as
being encryption or some such nonsense.

We have been attempting to close the link at 10 Mbps.

The demonstration of the link calculation given by Michelle and company at
Dayton was very useful in sensitizing people to the way these kinds of trade
offs are done.  Michelle has published on Namaste's site the link budget
calculations as updated recently with all of the assumptions that have gone
into the calculations.  

I am quite interested in doing a DVB-S demodulator for all sorts of reasons
even if a cheap card is available in an SDR setting.  Let me say that
personally, I have limited real time to devote to this development so others
may wish to take it on if it is not chosen by this group.  I would
personally prefer working on something we can come to a consensus is a way
forward to make the best use of the time I have available.

I am proposing as a personal project, not as the AMSAT way, just as a
demonstration,  using GnuRadio and USRP or USRP-2. The job I set for myself
has just been made a lot easier by Eric, K7GNU, in a new scheduling approach
inside GnuRadio.

73's
Bob
N4HY

ARRL SDR Working Group Chair
Member: ARRL, AMSAT, AMSAT-DL, TAPR, Packrats,
NJQRP, QRP ARCI, QCWA, FRC.
"Trample the slow ....  Hurdle the dead"


-----Original Message-----
From: namaste-dev-bounces at amsat.org [mailto:namaste-dev-bounces at amsat.org]
On Behalf Of William Blair
Sent: Monday, July 14, 2008 10:54 AM
To: namaste-dev at amsat.org
Subject: [Namaste-dev] DVB-S downlink format

I don't recall seeing a direct response to this suggestion.  Perhaps, I
missed it?  Specifically, I like the low-cost, receive-only earth station
using COTS hardware portion of the suggestion:

> Date: Tue, 1 Jul 2008 14:39:51 -0500
> From: "Howie DeFelice" <howie at aosusa.com>
> 
> I couldn't agree more with Bob's assessment of the
> uplink. Giving the transponder a channelized appearance will
> certainly make operation easier to understand and use. Since the 
> receivers are SDR, there is no reason channel bandwidths couldn't be
> changed individually so that high performance class ground stations > had
access to a larger variety of bandwidths (channels) than lower
> performance earth stations. 
> 
> Along those lines, I was thinking there might be a benefit
> to adopt a standard DVB-S downlink format, mapping channels 
> into PIDs in the downstream frame. The largest single benefit of
> this is that it allows beginners to assemble a receive only earth
> station using very low cost parts; i.e. PCI bus DVB receive card
> (under $100), C-band LNB (under $50), small antenna (under $50).

> What would be needed is the magic software that pulls the data out
> of the PIDs and sends them to the appropriate codec or socket. I 
> did a link budget based on a 2Mbps downlink using 3/4 rate viterbi
> with 188/204 Reed Solomom, QPSK modulation and the link closed into
> a .6 meter antenna. I used some of the worst case parameters
> discussed on the message board.  When I needed to estimate
> parameters, I used typical Intelsat specs for global beam
> edge of coverage.
> 
> OK, I know that build-it-yourself ground stations was not part of 
> the design criteria, but I thought it was worth putting out there
> for discussion...
> 
> Howie
> AB2S


      
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