Jim wrote:
Well, thanks for the replies so far. Obviously I won't be able to
hear NSA or AF1 etc even though they use the same frequency spectrum
for communication. Most likely they'd use spread spectrum and/or some
other kind of encryption. Theoretically any type of signal that can
be encoded can be decoded. So, am I correct that scanners can't
receive and decode ALL signals even if they are in standard AM, FM,
SSB modes?

I'd be dumbfounded if AF1 broadcasts in standard AM mode on 126.5 MHz
for instance. Thus, having a scanner that covers airband wouldn't be
able to receive AF1 communication.

You WILL, repeat WILL hear AF1 broadasts in the clear in standard AM on
the VHF and UHF aviation bands. You will NEVER hear AF1 calling ATC
(Air Traffic Control) in anything but standard AM modes on VHF, if they
did ATC would never hear them as ATC has no form of "kaptain krunch
encoding/decoding rings" in their facility.

Listen to this: http://www.milaircomms.com/audio/032603airforceone.mp3
This is AF1 in "standard" AM in Florida on March 26, 2003 I caught these
comms between Airforce One and Jacksonville Center (ATC). You'll hear
AF1 contacting several different sectors in the JAX Center area.
Frequencies this was recorded are 126.3500, 134.0000, 133.3250 MHz.

I guess your "dumbfounded" now....just kidding

George
http://www.MilAirComms.com