On Tue, 24 Oct 2006 17:35:41 GMT, Tauno Voipio
wrote:

wrote:
Tauno Voipio wrote:

The localizer signal is a combination of three signals


Whoah. Hang on. I've learned (from appropriate FAA publications) that
the localizer was made up of two signals, one modulated at 150 Hz and
the other at 90 Hz, each sent in lobes on either side of the centerline
and the localizer reciever just compares the relative strength of each
signal. Is that right, wrong, or overly simplified?

That's right - after the three components are combined in
the receiver antenna.

All the three components carry both 90 Hz and 150 Hz modulation,
but they are all different in such a way that being off the
centerline causes an increase of the modulation depth (sound
stregth) one modulation frequency and a decrease of the other.
This is where the phase differences are needed.

A very interesting discussion and nice to have a technical
explanation. It makes more sense as a simple signal strength change
would be likely to be unreliable.

Thanks for the explanation of the glideslope antenna. I always thought
it was the ground reflection that caused the unwanted lobe and had not
appreciated the ground was deliberately used to simulate the
underground antenna as well as introducing the extra unwanted lobe(s).