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

[Cory Papenfuss]

> 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.

	DME is up by the transponder frequencies...around 1GHz.  The 
glideslope signal is around 300Mhz UHF.

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.

	Some are localizer, not VOR within that frequency band.  Those are 
90 and 150Hz AM out a center line of the runway.  The nav instrument reads 
the strength of each to determine if centered down the runway.... centered 
needle=equal strength=lined up.  The glideslope signal is more or less the 
same (at different frequencies), but vertically oriented as opposed to 
horizontally.

> 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).

	I don't know if the FAA/FCC is working too hard on another split 
in the US.  From what I understand, some/(all?) countries in Europe are 
using an 8.33MHz split already.  I know I'll be pissed if they obsolete 
the radios I just put in my plane.....

 >
> 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.
	... and some do not provide even altitude information.  "Mode-A" 
provides only the 4 octal digit code assigned to them by ATC.  "Mode-C" 
also provides absolute static air pressure (from which ATC can correct for 
altimeter setting and get indicated altitude).


-Cory

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* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
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