[Ground-station] Baseband => decimation - questions

Ron Economos w6rz at comcast.net
Fri Jan 25 19:14:21 EST 2019


I'm not sure we are talking about the same thing yet. So what exactly do 
you expect to decimate and why?

Ron W6RZ

On 1/25/19 16:07, Michelle Thompson wrote:
> The beginning of wisdom being the definition of terms and all, it 
> would be good to make sure we're all talking about the same thing.
>
> So far, I've used LNBs and USRPs for receive, with the LNB doing an IF 
> at 618MHz (LNB-on-a-Stick) and giving reasonable performance.
>
> Decimation to me is a DSP thing, or used to reduce power consumption 
> when you don't need to sample as high as you can.
>
> -Michelle W5NYV
>
>
>
>
> On Fri, Jan 25, 2019 at 3:52 PM Ron Economos via Ground-Station 
> <ground-station at lists.openresearch.institute> wrote:
>
>     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>
>>     <mailto: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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