I've now started transmitting a timed beacon signal on
503.7kHz that is identical in format to that of GB3SSS operated over
the winter months of the last two years from Poldhu on 1.9 and
3.5MHz, and has a similar signal structure to the 5MHz beacons,
GB3RAL, WES and ORK. These all have an initial CW ident
and stepped power levels for aural reception, and a precisely
defined period of full-power plain carrier for S/N
measurements.
See
http://www.rsgb-spectrumforum.org.uk/5mhz%20beacons.htm
for the complete 5MHz signal structure. For this MF
transmission, as on GB3SSS, the pulsed sounder sequence of the 5MHz
beacons is replaced with a PSK31 message which lasts from 30s to
approx 48 seconds after the start
Auto Monitoring software writen by G3PLX is available for monitoring
these beacons, it measures signal to noise during the carrier period and
saves to file as well as plotting the last 40 hours worth of
measurements.
TIMING
The 503.7kHz transmission takes place every 15 minutes at 4 minutes
past the quarter hour.
ie each transmission starts at xx:04, xx:19, xx:34 and
xx:49 This time slot has been selected so
that the transmission do not interfere with my continuous ongoing
reception of the 5Mhz beacons - the active antenna used for these is
overloaded by the 500kHz signal and I have already lost data when the WSPR
beacon transmission coincided with one of the monitoring windows.
NOTE If using the G3PLX software, this
only monitors for the three 5MHz beacons at 00, 01 and 02
minutes.
SO IT WILL BE NECESSARY TO FRIG THE SOFTWARE
to monitor this transmission at the 04 minute
point. The necessary alteration can be done by firstly
setting your PC clock accurately to the correct time, then setting
the Track Time box to -240 (minus 240 seconds). This will make the
software look for this transmission during the time window it thinks
it would be receiving GB3RAL, and log the MF transmission during the
first minute, on the red trace, as if it were GB3RAL
The beacon uses the identical hardware to the WSPR transmissions
of the last few weeks, with the the only change being
a reprogramming of the controller PIC. In fact the very
same hardware was previously loaned to the Poldhu club for their beacons,
with the only difference being a change to the final Low Pass filter on
the output of the broadband PA.
