On Aug 6, 1:56 am, wrote:


Someone mentioned secondary surveillance. This is mode-s. It is also
on 1030/1090Mhz. However, the reply from the transponder is more
detailed. It contains a unique code for each aircraft. The older
transponders simply return the squawk code that was assigned by ATC
and entered by the pilot. Some mode-s can return airspace and
location.

http://mit.edu/6.933/www/Fall2000/mo...sb.tc.faa.gov/



Secondary "radar" is any type of system where the target is an active
particpant in the radio direction and ranging system. In the US civil
airways system this can be mode a/c/s and it is all the same (more or
less) technical description...

aka the main Secondary system sends out an interrogation pulse on one
frequency and the target replies on another. The times are measured
(ie time main pulse went out and secondary pulse recieved) and hence
range is achieved. Direction is based on the pointing of the primary
interrogator.

"Beacon" Antennas are commonly (but not always) co located with main
primary radar...they will generally be the "flat" rectangle on top of
the main (larger) antenna. They can stand alone...and that is common
in places like Canada and Austrailia...they require far less power
then primary or skin paint radars.

Beacon (ie secondary radar) was a US invention in WWII...It was called
"IFF" identification friend or foe".

What seperates a primary radar for ATC and one for WX are the
characteristics of the radar. Frequency is important but more so are
pulse repetition rate (PRR), polarization, and antenna rotation rate.
Most people think that there is one "echo returned" from a
target...this is not correct.

The PRR and antenna rotation rate are designed to maximise the number
of "Paints" of a target on a particular sweep.

Robert