Re: [Discuss-gnuradio] Modulation question

[Andrew Rich]

When you demodulate ads-b it becomes just square waves 

Sent from my iPhone

> On 30 Jan 2014, at 8:01 pm, Marcus Müller <address@hidden> wrote:
> 
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> Basically, yes, but that's communication theory. I'd refer you to
> Kammeyer -- Nachrichtenübertragung, but that's a German book. I guess
> Proakis would be a fine source, too, but I don't have his book at hand
> right now.
> 
> Anyway, ADB-S should *define* the pulse shape. Best look into Nick's
> gr-airmodes code for matched filtering; the matched filter directly
> gives you the transmission filter. (But that's even more signal theory)
> 
> Greetings,
> Marcus
> 
>> On 30.01.2014 10:44, Andrew Rich wrote:
>> Thanks Marcus
>> 
>> Pulse shape and repetition frequency determine bandwidth then ?
>> 
>> Square is the worst - gausian is better ?
>> 
>> - Andrew -
>> 
>> 
>> ----- Original Message ----- From: "Marcus Müller"
>> <address@hidden> To: "Andrew Rich" <address@hidden> 
>> Cc: <address@hidden> Sent: Thursday, January 30, 2014
>> 5:27 PM Subject: Re: Modulation question
>> 
>> 
>> Hi Andrew,
>> 
>> just a quick heads-up: I nearly missed your message because it was 
>> hidden in another thread, since you seem to have hit reply and
>> changed subject and text; however, my mail client recognized the
>> In-Reply-To header, and sorted you in - please directly write mails
>> unless you actually mean to reply.
>> 
>> So now for your question
>>>>> Ads-b uses a 1 MHz pulse position modulation scheme
>> On 30.01.2014 01:22, Andrew Rich wrote:
>>>>> Ads-b uses a 1 MHz pulse position modulation scheme
>>>>> 
>>>>> Is this possible to create on gnu ?
>> GNU Radio is only a software radio framework. Basically you can do 
>> anything with it that can be done in baseband signal of a sample
>> rate that your ADC/DAC and mixers (and analog filters, amps and so
>> on) support. With gr-air-modes there is a comfortable receiver
>> implemented in GNU Radio, and as a not-to-rough simplification you
>> can transmit everything with a software radio that you can receive
>> with one.
>> 
>>>>> 
>>>>> Is it the data rate that makes the spectrum wide ? 7 MHz ?
>> Ok, I don't really understand your question, could you please
>> elaborate? Reception of ADB-S works quite well with a 4MHz sampling
>> bandwidth, but I'm not quite sure on the technical requirements of
>> ADB-S transmission.
>> 
>> The actual bandwidth of PPM systems of course depends on pulse
>> shape and pulse frequency.
>> 
>> Hope I was able to help a little, Marcus
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