UK 5MHz Beacon Chain

The orginal UK 5MHz experiment used three time-multiplexed propagation studies beacons, operating on 5.290 MHz and became operational in mid-2003

The official 5MHz Experiment they supported has concluded, but two beacons continue to operate.

Regarding the current status of the UK 5MHz Beacons—

  • GB3WES is operational as per its original configuration below
  • GB3ORK was repaired and upgraded in July 2017 and now adds JT9A to its transmission
  • GB3RAL had local site issues and its licence has now lapsed

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Background

GB3RAL became operational in mid-2003, located at the Rutherford Appleton Laboratories, Oxfordshire, at IO91IN.

GB3WES, located in Cumbria at IO84QN, went live on 30 October 2004 and GB3ORK located on the Orkney Isles at IO89JA, went live at 0000z on 3 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.

For the first 30 seconds the three beacons follow the transmit sequence described by the following diagram:

5 mhz beacon sequence

GB3RAL the transmissions started on the hour, 15, 30 and 45 minutes past the hour with the call sign 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 nine steps the power resumes to 10W and the nine step sequence begins again.

From this point onwards the three beacons are different:

  • GB3RAL transmits a PSK31 identifier
  • GB3WES finishes transmission
  • GB3ORK transmits a 0.5mS pulse sequence at a prf of 40 Hz at full power. 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 one minute later than GB3RAL, and GB3ORK two 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 Call sign
00 GB3RAL
01 GB3WES
02 GB3ORK
15 GB3RAL
16 GB3WES
17 GB3ORK
30 GB3RAL
31 GB3WES
32 GB3ORK
45 GB3RAL
46 GB3WES
47 GB3ORK

The beacons have several features that were innovative when they were designed in 2003.

They include GPS time and frequency synchronization as well as fairly accurate 6dB transmit stepping.

A full write up of the design and construction can be found in the June 2005 (3-page/188KB PDF) and July 2005 (2-page/154KB PDF) editions of RadCom.

Auto-monitoring software

Peter Martinez, G3PLX wrote a freeware Windows program in 2003, which automates the process of monitoring and logging the reception of the three beacons.

The program carries out the function of a 1Hz bandwidth audio filter but can compensate for moderate amounts of frequency drift in the receiver and timing drift in the computer clock.

The monitoring program can either process audio from a conventional receiver or else the two I & Q audio channels from a direct conversion receiver.

The program also provides COM port switching for external devices, e.g. aerial switching, WSPR beacon, etc.

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 hosting GB3RAL,
  • John Linford, G3WGV for hosting GB3WES and
  • John Grieve, aka Donnie, GM0HTH for hosting GB3ORK
  • Andy Talbot, G4JNT, also needs special mention for designing and building the beacons—and…
  • 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 with the initial phase of the beacons, and not least to Ofcom for the necessary unattended beacon licences to enable these beacons to operate.