[Ground-station] Baseband => decimation - questions
Ron Economos
w6rz at comcast.net
Fri Jan 25 16:27:21 PST 2019
Okay. De-multiplexing is a much better and less confusing terminology.
As you stated, decimation is a DSP thing and channelizing the downlink
payload has nothing to do with DSP (all the DSP has already been down in
order to deliver payload packets).
Ron W6RZ
On 1/25/19 16:17, Michelle Thompson wrote:
> To me, decimation is what we do in order to channelize in the payload.
>
> I don't think that's exactly what I'm being asked about in the ground
> station receiver, though.
>
> -Michelle W5NYV
>
>
>
>
> On Fri, Jan 25, 2019 at 4:14 PM Ron Economos <w6rz at comcast.net
> <mailto:w6rz at comcast.net>> wrote:
>
> 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>
>> <mailto: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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