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

[Rick Parrish]

Martin Dvh wrote:

> 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)

I'll jump in on the air-band example:

108-118 Mhz is aero navigation; 50 khz spacing. The potential to 
construct a receiver with a 10 + mhz wide front-end that could 
simultaneously track up to "N" number of VOR or VORTAC ground stations 
would be very useful for classic "old school" aero navigation (old 
school meaning non-GPS). Traditional cockpit mounted NAV receivers only 
follow one signal at a time. A single VOR only gives you bearing 
information ... with two or more VOR signals you can triangulate. Some 
VOR stations also offer DME - a sort of distance ranging "ping" 
protocol. I think DME is up in the 300 mhz range so it would likely 
require a second receiver to capture this additional band. The VOR 
signal carries two components - a 30 hz reference and a 30 hz bearing 
signal. Comparing the phase of the two gives bearing (eg. 0 to 360 
degrees) to the VOR site.

118-136 Mhz is aero voice communication. Listening to a half-dozen 
simultaneous conversations isn't very useful for a pilot but being able 
to simultaneously scan dozens of air-band channels is a dream come true 
for many scanner enthusiasts. Fifteen years ago, channel spacing was 50 
khz, then split to 25 khz. The FAA and FCC may be working to split the 
band yet again (I'm way out of touch on some of this).

1030 - 1090 Mhz is the range for primary radar interrogation and 
aircraft transponders' replies. Some transponders provide only altitude 
information; others provide GPS XYZ coordinates. By capturing all of the 
transponder replies in a given area, you could build your own collision 
avoidance system.

-rick