GB3HM
Holbrook Moor

Specification (subject to change).

Receiver frequency 51.32MHz.
Transmitter frequency  50.82MHz.
Transmitter stability 80°C ovened crystal giving better than ±2ppm from -30 to +60°C
Peak deviation 2.4KHz.
Audio compression 4:1 above 1.5Khz limited @ 2.4Khz.
CTCSS frequency 71.9Hz group B.
CTCSS deviation 240Hz.
CTCSS sensitivity  (required deviation for access) ~120Hz @ 12db SINAD and better than 70Hz above 1uV input
Morse deviation 1.2KHz reduced to 450Hz with talk through.
RF output power 14dbW at antenna connector.
Spurious emissions better than -75db before the duplexer.
Receiver sensitivity better than 0.12uV for 12db SINAD (Signal-to-noise and distortion ratio).
Squelch sensitivity 2 stage 0.45uV falling to 0.12uV once open above noise floor.
Supply 240VAC mains with 55AH battery backup giving up to 60 hours standby and 9 hours active operation.

Cavities:
Receive chain forward loss 0.5db for a total notch of 113db
Transmit chain forward loss 0.5db for a total notch of 114db

Operation (subject to change).

A beacon consisting of the repeater's call sign, tone group and locator are sent in Morse code at intervals of ten minutes.  This beacon is sent independently of repeater status but can be modified by the repeater control software to reduce the audio level and shorten the transmitted string to call sign and tone group only.

To open the repeater a valid CTCSS tone and a signal stronger than 0.45uV must be detected. Once detected the transmitter and talk-through audio path are enabled and squelch sensitivity is increased to 0.12uV to aid weak or fluttery signals.  This signal condition must exist for more than three seconds for initial latch otherwise the repeater will immediately close.  Once latched a further 2 seconds of valid signal will fully latch the system.  On partial latch the removal of the signal will cause six pips to be transmitted, the first two pips will be at a slightly different frequency to the following four.  The change in pitch signals the timeout timer has been reset.   Fully latched a Morse 'K' character precedes  the pips.  The first two pips should not be interrupted or a timeout will result.  If the signal is lost for more than 0.8 second after full latch the 'K' will be omitted to indicate a broken received signal.  The 'K' is an invitation to transmit not an indication the timer has been reset.  This is a deliberate feature to allow fast turn around of overs but forcing a pause every few minutes to allow a break-in station.

1750 Hz tone operation is available but as this is not a normal mode for a six meter repeater we will see if  it is required and may turn it on at a later date.  As tone operation opens the repeater in carrier mode only the squelch sensitivity is maintained at 0.45uV to reduce the possibility of interfering signals.