[Hackrf-dev] Visualising 1090 MHz ADS-B

[Andrew Rich]

Ok I have just watched a video 

I is an amplitude sample in time
Q is an amplitude sample in time

They are just a little bit apart

So what does an SDR program do with the I and Q ?

How does it know when to start sweeping across the screen ? 

Sent from my iPhone

> On 9 Jul 2017, at 11:01 am, Andrew Rich <vk4tec at tech-software.net> wrote:
> 
> Ok my center frequency is 1090 MHz
> 
> The on off rate is 1 MB/s I think from memory
> 
> I have noticed the sampling rate determines the frequency span 10 MHz = 10 MHz
> 
> So there is a stream of I and Q coming out 
> 
> What is I and Q telling me ? 
> 
> Is I how far along the scan it is ?
> 
> And is Q telling me how big the signal
> Is ? 
> 
> Would an IQ file contain a whole heap of scans ? 
> 
> I = X axis
> Q = Y axis
> 
> I would need to sample fast enough as to not miss an amplitude change I want to see 
> 
> I guess an IQ file is not plain text but 8 bit numbers packed ?
> 
> Does it go IQIQIQIQ ?
> 
> What relationship is I and Q to the center frequency ? 
> 
> I think the signal amplitude resolution is described as 8 or 12 bits ? 
> 
> So as the ADC is pumping out numbers, which it has no control over , it is just sampling the signal.
> 
> Why does it not just out put values of amplitude ? Or is that what the I is about ? 
> 
> I am just trying to work out if I record 1090 MHz which is basically OOK on off keying, what would be contained in the file ? 
> 
> Am I right with the 8 bits , IQIQIQ ? 
> 
> Andy
> 
> Sent from my iPhone
> 
>>> On 9 Jul 2017, at 5:18 am, Cinaed Simson <cinaed.simson at gmail.com> wrote:
>>> 
>>> On 07/08/2017 06:44 AM, Gregory Ratcliff wrote:
>>> Great request!  I would like to see this also.
>>> 
>>> Greg
>>> Nz8r
>>> 
>>> Sent from my iPad
>> 
>> A flowgraph as in gnuradio?
>> 
>> Don't know.
>> 
>> How about a python script using qt and gnuradio?
>> 
>> Try
>> 
>>  https://github.com/bistromath/gr-air-modes
>> 
>> You'll need to build it - might need a development environment.
>> 
>> If you know what you're doing then you could probably build a flow graph
>> from gr-air-modes python scripts.
>> 
>> -- Cinaed
>> 
>> 
>> 
>> 
>> 
>> 
>>> 
>>> On Jul 8, 2017, at 6:23 AM, <vk4tec at tech-software.net
>>> <mailto:vk4tec at tech-software.net>> <vk4tec at tech-software.net
>>> <mailto:vk4tec at tech-software.net>> wrote:
>>> 
>>>> Hello Guys
>>>> 
>>>> 
>>>> 
>>>> I have a hack rf, GNURadio and MacBook Pro
>>>> 
>>>> 
>>>> 
>>>> Can someone point me towards a flow graph that would show me the
>>>> pulses on 1090 MHz 
>>>> 
>>>> 
>>>> 
>>>> Showing the preamble and 56 and 112 bits please
>>>> 
>>>> 
>>>> 
>>>> Andrew
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
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>>> 
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>> 
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