Re: [Discuss-gnuradio] Over the Air Signal Capture

[Martin Dvh]

address@hidden wrote:
> If anyone needs some more sample data captured, please let me know.  I 
> should have my USRP board today.  I'm in the Phoenix, AZ metro area and 
> would be happy to capture signal that may help in development of 
> processing blocks.
>
> Provide frequency, bandwidth, and sample length information.  I'll try to 
> help out.  I have antennas for DC - 3GHz.  Right now I'm thinking of a GPS 
> snapshot, 2m (144-148MHz), 70cm (440-450MHz) ham bands, and maybe a public 
> service band (455-465MHz) has a lot of narrow band FM activity.
If you are at it. A NTSC television channel would be nice. (I found a NTSC capture at http://comsec.com/data/ but it seems to have a high power 
interference signal at about 1 MHz)

RF Frequency: don't know what is in your area, just pick one.
bandwith:     6 Mhz
sample length: 0.15 seconds is enough for a few video-frames. a few second 
would be nice for audio.

Make sure you have at least 6 Mhz bandwidth to get the whole television 
channel. (Including audio)

Also know that The frequency of a  Television channels is most of the time said 
to be the frequency
 of the Video carrier which is NOT at the centre of the channel.
You can check with a fft graph.
The high peak is the video carrier. The whole channel is from 1.25 Mhz below 
that and  3.75 Mhz above.
So if you set the centre freq at:
rf_centrefreq = video_carrier_freq + 1.75 Mhz
and have a bandwith of at least
bandwidth =  6 MHz
you will be fine.

See the chart below for specifications of NTSC channels:
http://www.mastervideo.com/ntsc_chart.htm

NTSC-example
BROADCAST-channel#     MHz        VIDEO-carrier    SOUND-carrier
21                     512-518    513.25           517.75


Also nice would be air-traffic control samples.
These are narrow AM-modulated in the 120-130 Mhz band.
I think a bandwidth of 10 or 20 kHz should do (didn't check for exact specs yet)
length: if there is a transmission 10 seconds would be enough.

I think the following should be receivable in your region:
Phoenix Sky Harbor Airport:
Automated Traffic Information Service
121.2 MHz (current airport conditions)

Approach Control
North - 119.2 and 120.7 MHz
South - 123.7 and 124.1 MHz

Control Tower
North runway - 118.7 MHz
South runway - 120.9 MHz

Ground Control (controls aircraft on the taxiways and ramps)
North - 119.75 MHz
South - 132.55 MHz

Clearance Delivery (gives airlines their final routings and clearances)
118.1 MHz

thanks and greetings,
Martin