In article Bob Kuykendall writes:
On Apr 11, 2:33=A0pm, "Paul Remde" wrote:
... =A0At a recent soaring
seminar someone stated that they thought the FAA was
going to require radios with the 8.33 MHz spacing starting in 2020.

If they said that, they were confused. Especially since 123.3 and
123.5 are only 0.2 MHz apart. It's 8.33 kHz.

I see it as taking quite a while before it would become mandatory.
How long did it take to make the tighter frequency tolerances mandatory
when 720 channel radios became the norm? Quite a few years, as I recall.


I will be someewhat surprised if we get to 2020 and we are still using
what we think of today as "aircraft radios." I think that by then we
will find that the bandwidth dedicated to those old grampa boxes will
have been divided up and auctioned off, and we will be communicating
over a system based on mobile phone infrastructure.

This I don't believe. First off, auctioning off the bandwidth would
not work, since aviation is international, and includes those airliners
that come from other countries that are not into auctioning off spectrum.
A major change would involve international agreements and take some time.

Second, a mobile phone infrastructure system would be using ground
based cell towers (which are not reachable in much of the world, and
not even at an airstrip where I have flown). Also, cellular systems
work by frequency reuse, which requires the limited range of the cell
sites to the mobile phones to make reuse possible within a reasonable
distance. When you are at 10,000 feet, the horizon is about 120 miles
away, so those radio signals will go a long ways, and frequency reuse
becomes more difficult.

Third, there are folks who will reasonably not want their aircraft
communications to be dependent on ground based resources. Presently
even with no functioning ground resources for hundreds of miles, an
aircraft radio on the ground can communicate with one in the air.

Alan