[Ground-station] Baseband => decimation - questions

Ron Economos w6rz at comcast.net
Fri Jan 25 18:51:08 EST 2019


The standard IF for DVB-S2 receivers is 950 to 2150 MHz.

DB6NT was selling a down-converter from 10489-10500 MHz to 1129-1140 MHz 
for P4A.

https://shop.kuhne-electronic.com/kuhne/en/shop/new/MKU+LNC+10+OSCAR+P4A/?card=1832

I'm not sure what decimation has to do with receiving DVB-S2. The entire 
10 MHz signal needs to be demodulated. Individual baseband frames will 
be selected for processing, but I call that de-multiplexing.

Ron W6RZ

On 1/25/19 15:32, David Vieira via Ground-Station wrote:
> Michelle - Thanks for posting.  I'll frame some of the questions.
>
> Typical 10 GHz terrestrial contesting rigs are Heterodyne; that is a 
> Mixer works with a Local Oscillator (LO) to take the RF down to an IF 
> (Intermediate Frequency).
> For an SDR, that IF can be digitized by an Analog-Digital Converter.
>
> The most popular IF for contesting/SSB rigs is 144 MHz.
> For a data BW of 10 MHz that may or may not be a fast enough IF 
> carrier.  If we can digitize and recover the data, it would allow a 
> lot of re-use of existing equipment.
>
> I've heard suggestions/proposals up to the 1.2 GHz Ham band.
> In some sense, the IF carrier could be 144/220/440/915/1200 MHz, or 
> even any Non-Ham frequency in between.
>
> There are a lot of proof of existence designs for a 10 GHz Mixed down 
> to an IF; and lots of off the shelf ADC dev-boards.  (catch me off 
> thread for details).
>
> Some questions I have are:
> ---from an FPGA side of the SDR, what data rate(s) can the FPGA absorb 
> in to a decimator?
>
> Must we decide upfront on a single frequency; or
> preferably allow flexibility in the RF front end design (ie, Mixer, 
> PLL and Local Oscl hardware choices) by allowing a wide and 
> programmable variety of ADC and decimation rates?
>
> {This is where RF and Digital folks must communicate across walls.}  ;-)
>
> Comments welcome.
>
> regards,
> David
> KI6CLA
>
>
> On Friday, January 25, 2019, 2:41:54 PM PST, Michelle Thompson via 
> Ground-Station <ground-station at lists.openresearch.institute> wrote:
>
>
> While we are striving to enable all sorts of wonderful designs by 
> putting prototypes into GNU Radio, a central goal is to design our own 
> hardware.
>
> We've had a lot of progress on the protocol and algorithm front (GSE, 
> LDPC, some of the polyphase).
>
> Some fundamental decisions about our own hardware need to be made.
>
> When we receive, we expect to have to decimate. This is because we are 
> receiving at a relatively high frequency (10GHz).
>
> Our bandwidth is (up to) 10MHz. For DVB-S2/X, we fix our sampling 
> rate, depending on what bandwidth we want to support. We have a lot of 
> freedom here.
>
> Picking the right frequencies for the receive chain is therefore 
> important.
>
> What are our options?
>
> What options make the best sense?
>
> I'd like to build and test as soon as possible, so let's get some 
> discussion going.
>
> -Michelle W5NYV
>
>
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