|As of 26.09.12, this page becomes
the home page for the 3cm Mow Cop .....................................receiver
running via WebSDR
|The same antenna and LNB combination that was used
for the Bawdsey receiver is used here, but a different IF
is employed, based on an '80m Finningley SDR' board. In a
bit of a Heath Robinson arrangement, the on-board 15 MHz
crystal oscillator is replaced with an
oscillator/multiplier board using a 12.570 MHz crystal
multiplied by a factor of 6 to 75.420 MHz (in fact, it's
another of the same multiplier boards used in the
front-end 'Berniebox'). This results in an IF
coverage of 18.855 MHz +- 48 kHz.
Output from the SDR feeds an SoundBlaster AudigyZS sound card fitted to the server.
There are 12 pairs of slots resulting in a gain
of 13.5dBi. Extensions, or wings, added to the
narrow waveguide face reduce the variation
in azimuthal gain to about +-2.3dB.
(view radiation pattern picture in a seperate)
(antenna pics/plot courtesy of David Wrigley)
||This particular LNB is
manufactured by WNG, and
the 22mm coupler is a good tight intereference fit,
which means that the mating copper tube wave-
guide can be rotated without having to worry about
the coupler itself rotating or coming loose, which is
actually quite a useful feature.
Probe skew (relative to the eliptical feed horn)
ensures that it is not obvious what the correct
alignment is for the copper tube waveguide, so
being able to rotate this for best signal-to-noise
ratio is very useful.