5MHz Beacons   
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The Beacons
There are three identical propagation-studies beacons operating on 5.290MHz.  GB3RAL has been operational since mid-2003, and is located at the Rutherford Appleton Laboratories, Oxfordshire, at IO91IN.  GB3WES, located in Cumbria at IO84QN, went live on 30th October 2004 and GB3ORK located on the Orkney Isles at IO89JA, went live at 0000z on 3rd December 2004.  All three beacons transmit at a nominal power of 10W. GB3RAL employs a dipole aerial, GB3WES and inverted V dipole and GB3ORK uses a 90ft long inverted V dipole, 21ft high in the centre, feed with a 1:1 current balun, orientation E-W.  All three transmit the sequence described by the following diagram: 

For GB3RAL the transmissions start on the hour, 15, 30 and 45 minutes past the hour with the callsign being sent by CW at full power.  This is followed by a short period at full power (10W) before the transmission steps down by 6dB every second.  After 9 steps the power resumes to 10W and the 9 step sequence begins again.  Following that there is a period of full-power and the last 30 seconds of the transmit sequence is completed with a 0.5mS pulse sequence at a prf of 40Hz.  This is to allow a specialist measurement of multipath and Doppler shifts to be measured along the path.

The transmit sequence for GB3WES and GB3ORK is similar except that GB3WES starts transmissions 1 minute later than GB3RAL, and GB3ORK 2 minutes later than GB3RAL.  Note that the short 100mS gaps between steps has only been implemented in the keying sequence for GB3WES and GB3ORK. The short transmission gap is there is improve readability of the steps.   Thus the transmit sequence for the beacons are: 

                                                                       

Minutes past each hour

Callsign
00 GB3RAL
01 GB3WES
02 GB3ORK
15 GB3RAL
16 GB3WES
17 GB3ORK
30 GB3RAL
31 GB3WES
32 GB3ORK
45 GB3RAL
46 GB3WES
47 GB3ORK

 

In due course it is planned to have calibrated field-strength measurements of all three transmissions.

Acknowledgements

In putting together this beacon chain it is important to recognise the efforts put into the project by the three Beacon Keepers:  Mike Willis, G0MJW and RAL for building and hosting GB3RAL, John Linford, G3WGV for hosting GB3WES and John Grieve, aka Donnie, GM0HTH for hosting GB3ORK.   Andy Talbot, G4JNT, needs special mention for designing and building the PIC control unit for GB3RAL and for designing and building the complete systems for GB3WES and GB3ORK.  Peter Martinez, G3PLX, for his untiring work to support the beacon project with free automated beacon-monitoring software, as well as the more specialist work involved in the study of Doppler and multipath propagation from the beacons.  Our thanks are also due to Yaesu(UK) and SMC for their support, and not least to the RSGB and OFCOM for their swift processing of the necessary un-attended beacon licence paperwork to enable these beacons to get on-air!

 
Copyright 2005 RSGB. All rights reserved.  
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