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.
