Posted by Paul Coffman on
URL: https://www.es-forum.com/metal-does-block-fm-radio-tp1545429p1545441.html

Here's the descriptions from wikipedia of the 2 things they have at the
airport: ILS and VOR. Doesn't anything in these explanations stand out to
you as being particularly problematic, moreso that a normal fm radio wave?
For the ILS, I live near a small regional airport, so the beam is NOT
locallized to allow for a backcourse, which means I am exposed to it:

ILS:

A localizer (LOC, or LLZ in Europe)
antenna<http://en.wikipedia.org/wiki/Antenna_%28radio%29>
array <http://en.wikipedia.org/wiki/Phased_array> is normally located beyond
the departure end of the runway and generally consists of several pairs of
directional antennas. Two signals are transmitted on a carrier
frequency<http://en.wikipedia.org/wiki/Carrier_frequency>between
108.10 MHz and 111.975 MHz. One is
modulated<http://en.wikipedia.org/wiki/Amplitude_modulation>at 90 Hz,
the other at 150 Hz and these are transmitted from separate but
co-located antennas. Each antenna transmits a fairly narrow beam, one
slightly to the left of the runway centerline, the other to the right.

In addition to the previously mentioned navigational signals, the localizer
provides for ILS facility identification by periodically transmitting a 1020
Hz morse code <http://en.wikipedia.org/wiki/Morse_code> identification
signal. For example, the ILS for runway 04R at John F. Kennedy International
Airport <http://en.wikipedia.org/wiki/John_F._Kennedy_International_Airport>transmits
IJFK to identify itself to users whereas runway 04L is known as
IHIQ. This lets users know the facility is operating normally and that they
are tuned to the correct ILS. The glideslope transmits no identification
signal and therefore airborne ILS equipment relies on the localizer for
identification.

Modern localizer antennas are highly
directional<http://en.wikipedia.org/wiki/Directional_antenna>.
However, usage of older, less directional antennas allows a runway to have a
non-precision approach called a localizer back course. This lets aircraft
land using the signal transmitted from the back of the localizer array. This
signal is reverse sensing so a pilot may have to fly opposite the needle
indication (depending on the equipment installed in the aircraft). Highly
directional antennas do not provide a sufficient signal to support a
backcourse. In the United States, backcourse approaches are commonly
associated with Category I systems at smaller airports that do not have an
ILS on both ends of the primary runway.

VOR:

VORs are assigned radio channels between 108.0 MHz (megahertz) and 117.95 MHz
(with 50 kHz spacing); this is in the VHF (very high frequency) range.

The VOR system uses the phase relationship between a reference-phase and a
rotating-phase signal to encode direction. The carrier signal is
omni-directional and contains the amplitude modulated (AM) station Morse
code or voice identifier. The reference 30 Hz signal is frequency modulated
(FM) on a 9960 Hz sub-carrier. A second, amplitude modulated (AM) 30 Hz
signal is derived from the rotation of a directional antenna array 30 times
a second. Although older antennas were mechanically rotated, current
installations are scanned electronically to achieve the same result with no
moving parts. When the signal is received in the aircraft, the FM signal is
decoded from the sub carrier and the frequency extracted. The two 30 Hz
signals are then compared to determine the phase angle between them. The
phase angle is equal to the direction from the station to the airplane, in
degrees from local magnetic north, and is called the "radial."




On 10/21/07, Bill Bruno <[hidden email]> wrote:


--
Paul Coffman


[Non-text portions of this message have been removed]