19th June 2013
On a clear night, this beacon is easy to find using 4"
optics at the Fulbourn Hill site (regularly used by the
CDARC and Camb-hams)
There were two reasons for installing an IR beacon -
firstly to provide an alternative beacon, this time
aimed at Fulbourn hill, which is way off the red
beacon main beam, and secondly to have one running
at a sufficiently different wavelength that the
effectiveness of receive filters could be
investigated. It was also felt that an IR beacon
might be more tolerant of day-time light levels.
The nominal beacon beams are:
a) Red - circular +-10 degrees centred on 122
degrees from Wyton
b) IR - elliptical beam, +-10 deg azi, +-2 deg
ele, centred on 135 degrees
The elevation beamwidth was reduced because it was
felt that cloud/forward scatter propagation at the
power level involved was not a very useful mode to
Target erp is further increased by running the 10
LEDs at fives the current of the red beacon. LED
efficiency figures are only available for the IR
emitters, but assuming that they are roughly equal,
the on-beam signal level some be about 15 dB greater
for the IR beacon. It will be interesting to
discover if this is so in practice!
This beacon is baseband modulated with a simple
two-tone square wave drive source, the two two tones
being nominally 1 kHz and 1.05 kHz. The
repetition rate is approximately 250 msec.
********** REPORTS OF BEACON RECEPTION GRATEFULLY