plot
Predicted coverage area


spare
        Main and standby 3cm beacon units


pa
              1W PA and driver module


ant
 3cm Waveguide slot antenna and location


East

south

west
north

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3cm beacon keyer:  IK0WRB

GB3CAM    Cambridge microwave beacons
IO92WI          Wyton           Cambridgeshire                                                                                                         
 
3cm:  10368.755 MHz                                1.2cm:   24048.870 MHz

reports always welcome, either direct ( gb3cam[at]earf.co.uk ) or via www.beaconspot.eu                       
                                                                                                                                                                                      


     The two beacons had their first annual maintainance on the 22nd July, and both frequencies were reset to their nominal frequency



The first of the two Cambridge microwave beacons came on-air on 11th June 2008. This was the 10 GHz
beacon.  Although Wyton is only some 35m asl, the beacon antennas are 30m above ground level - well
above the local tree cover. There is some obstruction due to other antennas on the same site however.
.
beacon-details
 

beacon antennas		 LHS:  24 GHz multiplier/PA/antenna.                         
RHS:  10 GHz antenna.

These units are mounted on the eastern side of the  tower (the camera is looking SE).

cabling
 The antenna's are located about  
15m from the rack.

On 3cm, the transmitter power
is 3W, but this is reduced by loss
in the cable to 0.5W at the
antenna.
 



      3cm 'Spots' added to www.beaconspot.eu                          3cm Beacon     -     1st year frequency error
                during the first year of operation
beaconspot             1sy year drift  



 
3cm beacon frequency error history during 2nd year, following re-netting
ie, latest  measurements
  (measured every Wednesday against a rubidium standard):
Measurement date
 22.07.09
 29.07.09
   05.08.09 
12.08.09
 19.08.09
         drift
Error
 -30Hz
 -95Hz
 -70Hz
 +115Hz
 -120Hz






Measurement date 26.08.09 02.09.09
 10.09.09
 16.09.09
 23.09.09
Error -70Hz
 -90Hz
 -180Hz
 -110Hz
 -105Hz






Error
 30.09.09
 07.10.09
 16.10.09
 20.10.09
 28.10.09
Measurement date
 -95Hz
 -75Hz
 -175Hz
 -120Hz
 -140Hz






Error 11.11.09
 18.11.09
 25.11.09
 02.12.09
 09.12.09
Measurement date -175Hz
 -160Hz
 -175Hz
 -185Hz
 -185Hz







Error 16.12.09 23.12.09
 30.12.09
 06.01.10
 13.01.10
  20.01.10    27.01.10      03.02.10
Measurement date -230Hz -205Hz
 -195Hz
 -246Hz
 -205Hz
   -205 Hz        -250Hz         -195Hz

  The reference oscillator used in this beacon is a 25 year old Racal 9420 unit. It operates at 5 MHz.

  There is short term drift in the order of +- 10 Hz, due to the combination of controlled oscillator drift and high loop
   time-constant, and as can be seen from these graphs, a long term stability of about +- 75 Hz, due to drift in the
   5 MHz reference.

  Something to think about: A 500 Hz error at 10 GHz equates to a clock that gains or loses 1.5 seconds per year.
For more 1.2cm details see:  http://homepage.ntlworld.com/john.g4bao/page12.htm         For more 3cm details see: http://www.earf.co.uk/3cm_proposal1.htm