[Boatanchors] SpaceShip One uses AM

[w8au at sssnet.com]

Sheldon Daitch, WA4MZZ, said:

> I was told years ago that one of the reasons for
> aircraft staying on AM was related specifically to the
> heterodyne effect, that is, one could almost always tell
> if two (or more) stations were transmitting at the same 
> time, so information could be repeated, if necessary.

Not quite that way.

>From working at ARINC, (Aeronautical Radio, Inc) years back, I found this 
was intentional.

ARINC had/has a national network of ground based VHF AM remote stations, 
all tied to their dispatch center via landline network.  Frequency was 
typically 130.4 mHz.  Each consecutive ground remote transmitter was tuned 
to a variation of the 130.4 channel, such as 129.996, 130.400, and 130.404.
(I don't remember the exact spacing, but this is an example)
When calling a commercial aircraft, all remote xmts would come up at the 
same time. So, to avoid massive QRM, the aircraft would copy mainly the 
one that was closest to him, and the others would be a minor high pitched 
heterodyne.
The aircraft receivers were wide enough to accomodate this.

Old technology, but effective...

Perry    w8au