GB3UHF Beacon Technical Details

The heart of the beacon is the frequency generator based on the OZ2M next generation beacon (NGB) system.

The 1 GHz PLL/VCO synthesiser reference is a G3RUH 10MHz GPSDO (Global Positioning System Disciplined Oscillator). This beacon includes some of the latest technology and modulation methods.

The 1 GHz VCO/PLL synthesiser uses an ADF4107 PLL that is controlled by an Atmel ATmega328 and a Crystek CVCO55CX-1000-1000 ultra low noise VCO using the 10MHz GPSDO reference and generates a signal of which the output is applied to the DDS. The DDS generates a signal at 432 MHz by using sampling techniques of an AD9912 which is controlled by an Atmel ATmega128A. The output at low level is low-pass filtered (using a filter suplied by Sam Jewell G4DDK) and amplified by a Class-A MCL RF amplifier and then level adjusted before passing to the PA. The G3RUH PLL reference 10MHz oscillator that has an oven controlled crystal oscillator (OCXO) which is disciplined by reference to GPS signals. A spare 10MHz OCXO (not GPS disciplined) is now kept on site for emergency use only if the main GPSDO fails. If this is brought into use then the beacon will send only the CW ident and a notice will appear on this site giving the current status.

The beacon frequency reference accuracy after warm up is better then 1010 after 30 mins with increasing improvement in accuracy. The frequency of the CW carrier (mark) being exactly on 432.430000MHz.

Both the frequencies used for CW FSK and JT65B are controlled by the DDS that also takes the GPS NMEA data to give the identification timings.

The beacon sends its callsign and locator in Morse, and uses F1B keying (FSK) with a 400Hz standard shift.

To enable the beacon to be monitored at extreme ranges, the beacon also transmits its callsign and locator using WSJT JT65B mode.

The GPS also provides for the precise timing of the keying sequence, such that the Morse sequence will start at every odd minute past the hour and for 14 seconds duration and the JT65B sequence will start at every even minute past the hour for 48 seconds duration. The keying software uses the same sequence as GB3VHF.

In the event of GPS lock being lost, the beacon will continue operation but with reduced frequency and timing accuracy until such time as GPS lock is re-established. When this occurs the JT65B sequence is suspended and replaced with the Morse sequence until GPS lock is re-established.

The component parts of the driver unit

The driver front panel indicators

Listen to the complete keying cycle

Full details of the Next Generation Beacon system can be found on Bo Hansen OZ2M's website

The beacon’s PA unit is based on the Mitsubishi RA60H4047 power amplifier module for the PA with components supplied by Chris Bartram GW4DGU and Grant Hodgeson G8UBN. The use of extensive RF filtering throughout ensures that the beacon complies with the most stringent CEPT regulations for transmitters operating in the UHF frequency range. Both in-band and out-band spurious signals are suppressed to better than -65dBc. The PA uses only heat sink convection cooling and no extra fan cooling is provided or needed under any environmental conditions.

The output from the driver unit is 13dBm (20mW). This drives the PA unit to produce a beacon maximum final power output of up to 15dBW (30Watts). This is further filtered by a high power low-pass filter which was built by Sam Jewell G4DDK and then monitored with a Bird Thruline power monitoring panel that shows both forward and reflected power simultaneously. Finally the RF is routed through a circulator that is used to protect the PA from high SWR fault condition and also to prevent intermodulation occuring in the PA due to the close proximity of the 2m beacon antennas

The PA unit and PSU

The beacon’s power supplies delivering 12 Volts, were sourced by David Bowman, G0MRF. The 12 volt PSU for the beacon driver unit uses a Mean Well RS25-12 2.1A RF proof medical grade switched mode PSU, and is followed by a conventional 8 volt regulator for the NGB VCO/PLL and the NGB DDS. The 12v is used for the G3RUH GPSDO. The 12v PSU for the PA is a low noise and RF proof Mean Well 709-NES350-12 SMPSU that can deliver up to 29A . All PSU’s use only convection cooling and no extra fan cooling is required under any environmental conditions.

Chris Whitmarsh, G0FDZ, the beacon keeper, integrated both the driver and PA units, and produced the metalwork and housing facilities for the beacon. The beacon was designed so that the driver and PA were built as separate units to ease access and maintenance. All connections are brought to the front on the units for the same reason. External connections to the beacon are simply mains power, GPS antenna and the main antenna system. Like most commercial systems, all the beacon units are built in 19 inch rack mount style, and the whole beacon which occupies a rack space of 9U shares a rack of 18 U, together with the GB3VHF 144MHz beacon.

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