GB3JB Hardware and Schematic

Motorola DR3000 Repeater

The image opposite, shows the Motorola equipment now installed at the GB3JB site. Providing the 2m DMR connectivity to the South West Cluster, as well as stand-alone independent coverage across the same 2m foot print.

It is a 25 watt output device which is reduced in output power, so as to comply with our 14 dBw (25w) ERP, NoV.

The rear image shows the standard configuration. Our unit has had the mains PSU removed, and the cooling fans.

It now runs directly from a 13.8v dc supply, and is convection cooled.

The schematic below, will give more detail.

The VHF Cavities

Opposite are the commercial VHF cavities.

On the left are the TX pair with the RX pair on the right.

These devices, along with the VHF circulator, and tuned coaxial interconnections, provide over 102 dB of isolation between the RX input socket and the TX output socket, of the DR3000 repeater.

This level of isolation enables GB3JB to operate with a single antenna being used for simultaneous transmit and receive.

You will note that the cavities are laid on their side and slewed at an angle.  This was the only way we could get them to fit inside the cabinet.

The NEW schematic for the DMR system, is as of May 2022.

The four solar panels each comprised of 72 cells, in a 6 x 12 array, measuring 1.6m x 0.9m.  The top two are rated at 250 watts peak and the lower two at 190 watts peak.

The nominal full load output voltage is 35 volts dc. The off-load fully illuminated voltage rises to approx., 54 volts dc.

As will hopefully be appreciated, 880 watts worth of power even at 35 volts D.C., can give you quite a wakeup call.

These types of panel are not to be played with. Hence they are mounted high up on the tower, well above the anti-climbing panels, the anti-climbing paint.

The wind turbine is rated at 150 watts at a nominal 24 volts dc.  However as with all wind turbines, that rating is when at maximum output, i.e. just before it ‘feathers’ or rips itself to bits.  At the average wind speed at the site, 5 to 6 m/s we see around 40 watts of energy supplied.

It will be appreciated that during peak winter months when there is little direct sunshine and quite often not a lot of wind, we can often suffer from power outages.

The security / CCTV etc., has it’s own separate battery support system.

Power Supply

All the site systems are powered by Solar Panels and a Wind Turbine, which operate at a High Voltages.

These various voltages are regulated down to a nominal 24 volts d.c. to charge the battery banks that power the various systems.

  • The GB3JB Repeater.

  • The GB3USK 23cm Beacon.

  • The Security & CCTV facilities which operate 24 hours a day and have an independent battery bank.

To give some idea of size of the individual solar panels, the image shows the late Clem G3UGR, standing next to our original panel.

Unfortunately, this was stolen.

However we got some solace in the knowledge that the individual who stole it probably thought it was 12 volts, and would have paid a heavy price when he plugged it into what was probably a 12 volt caravan system.

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