-----Original Message-----

From: Mxsmanic ]

Posted At: Saturday, January 20, 2007 8:09 AM

Posted To: rec.aviation.ifr

Conversation: How wide is an NDB approach course?

Subject: How wide is an NDB approach course?



Matt Whiting writes:



That is pretty neat. Yes, I used 1490 in Wellsboro for practice at
N38.

It isn't exctly aligned with the runway, but is close and we made
up a

little home-made approach for practice. It worked well.



I think the NDB concept was deliberately designed with this in mind,

so that ordinary radio stations could be used for emergency navigation

in a pinch. The frequency range is the same as AM radio, and I hardly

think that a coincidence.



--

Transpose mxsmanic and gmail to reach me by e-mail.



Think back even further to the low frequency radio ranges. This is the
bottom range on the old Bendix coffee grinder ADFs. The LF signal could
be "heard" over an extraordinarily long distance with relatively low
power. LF was around for navigation before AM radio really found its way
into aircraft. From Wikipedia:



"These radio aids became the navigation resource for enroute airways
flying in clear and clouded weather, and for airport letdown approach
patterns in limited ceiling and visibility conditions. Fixed emplacement
of low frequency, non-directional radio beacons came into use as
distance checkpoints along airways and along airport approach patterns.
Many, but not all of these low frequency systems were superseded after
World War II by higher frequency (hundreds of megacycles instead of
hundreds of kilocycles) radio wave emitting installations known as
"omni-range" and "localizer" facilities. This changeover to higher
frequency constituted an advance in degree but not in kind."