VOR is line of sight so the same frequency can be used over
and over as long as there stations are located far enough
apart and the "service volume" is protected. If you look at
the useable distance for a VOR signal, you will see that
very high altitudes are shorter range than lower and middle
altitudes because the interference is greater at high
altitudes.

Better quality radio receivers can reject interference,
radio band width can't be increased because all the
available frequencies have been assigned. But by making a
channel narrower, you can double the number of possible
channels each time you narrow the channel. Going from 100
KHz to 25 KHz quadrupled the number of channels. Forty
years ago, 90 comm. channels and 50 VOR was common and now,
Comm. channels are in the thousands. VOR is less suited to
adding more and more channels because of the location
issues.

If you have 108 to 117 for channels and you can only tune
whole numbers, you get ten channels. If you can tune 108.5,
you get 20 channels. If you tune 108.1 you get 100 channels
and 108.010 gets a 1,000. But if the power is high, it is
harder to reject the nearby station.

The FAA flight tests naviads and one of the issues is clear
radio reception.


--
James H. Macklin
ATP,CFI,A&P

"thejim" wrote in message
ups.com...
| This question relates to VOR.
| I read that when VORs where increasing continuously in
number in the
| beginning of their "career" there was a lack of available
frequencies.
|
| So they increased the frequencies by increasing the
number of chanels
| and they did that by decreasing the chanel width e.x from
100kH width
| to 50kH width.
|
| Can you explain me please how this(meaning increase of
channels by
| reducing their width) will increase the number of
available frequencies
| for the increasing number of VOR stations.
|