LF: Multi-function beacon

[Andy Talbot <andy.g4jnt@googlemail.com>]

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.

The software can be downloaded from  http://www.rsgb.org/spectrumforum/hf/beaconauto.php .   PSK31 data can be copied with Digipan, Fldigi, PSK31SBW or a host of other packages.

 

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.

 

Andy  G4JNT

www.g4jnt.com