GB3HM
Holbrook Moor

A six meter repeater located north of Derby serving Derbyshire, Nottinghamshire and beyond. 
Output on 50.82 MHz, input on 51.32 MHz with a CTCSS of 71.9Hz group B. 

Also, check out the new 70CM repeater MB5HM at the same site on Holbrook Moor.
This is a FX5000 with the same G8LMX logic board as GB3HM.
Output on 430.875 MHz, input on 438.475 MHz (7.6 MHz split) with a CTCSS of 71.9Hz group B.

Status: fully operational.

A little bit of information about GB3HM.
A low band Philips FX5000 repeater has been modified from 70 MHz down to 50 MHz.  This gives us a receive sensitivity better than 0.18uV for 12db SINAD and a programmable output power from ten to fifty watts. Our output power is currently set at 14dbW (25W).  The logic board has been developed by G8LMX to fit in place of the original RCM PCB inside the control unit, consequently no external logic is required.  The microprocessor is a Microchip 16F1947 running at 32MHz.  This has sufficient power for a multitasking environment and concurrently serves the repeater logic, IIC clock module, two bi-directional serial ports, two independent software Morse code generators, 1750Hz tone decoder and a host of internal time-slice and timed functions.   All logging, configuration, status and functional commands are done via the serial RS232 connector on the rear of the repeater chassis. The receiver and transmitter driver modules each have their own processor controlling the synthesisers.  Operation of the repeater is completely stand-alone but an attached PC gives logging, control and other functionality.  All add-on boards use the existing connectors so few modifications need to be done to the raw units to produce a fully functional repeater.  The modifying of a low band (E0 66 - 88MHz) unit down to 50MHz is another story (definitely not for the faint of heart).

The duplexer is constructed using six quarter wave cavities giving an isolation in excess of 100db for a forward loss of ~ 0.5db.  The cavities have been designed by G8LMX and built from scratch by G8LMX and G8OAD using 150mm construction grade aluminium for the outer tube with 45mm diameter resonators and 25mm thick end caps making a very rigid construction.  Tuning rods are invar steel alloy for temperature stability and a unique plunger design prevents noise even after prolonged usage in a damp, hostile environment.  The coupling loops, made from 4mm silver plated copper tube, are tuned and designed for temperature stability.