[Boatanchors] SpaceShip One uses AM

[sdaitch at ibb.gov]

Perry,

I understand what you are saying, but I thought that ARINC 
was later in the picture than ATC/tower operations, and 
the holdover was for actual ATC transmissions, that with AM,
it was very evident when two stations transmitted, and for
safety of flight purposes, the heterodyne indicated that
perhaps someone did not hear an ATC order/request, and 
could ask for a repeat.

The ARINC "method" you described might work, but if the two carriers
were more than, say 10 kHz apart, you aren't going to hear much
of a beat note anyway, and certainly not, if they are 20 kHz or more
apart.

Anyway, thanks for the additional input.

73
Sheldon
WA4MZZ

----- Original Message -----
From: w8au at sssnet.com
Date: Thursday, October 7, 2004 3:15 am
Subject: Re: [Boatanchors] SpaceShip One uses AM

> 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
> 
> 
> 
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