GB3OK Technical Specifications
GB3OK Repeater


Frequency Output 439.5125 MHz, Input 430.5125 MHz 70CM ( DVU41) ANALOGUE
TX RX Split Plus 9 Mhz Split
Location Chelsfield, Kent. J4 M25
Locator JO01BI or NGR TQ497643
CTCSS Tone "D" 82.5hz (CTCSS access only)
Station ID Morse GB3OK D sent interval 15 minutes at 18 words per minute "OK" for Orpington, Kent borders.
Mode of Operation Wide-Band FM (25 kHz)
Timeout 3mins, The time-out will be indicated by a “beeping” tone
Hang Time 6sec, To re-accessed with a carrier supporting a proper CTCSS tone and speech
Anti-Kerchunker 2sec keep weak signals from chattering repeater
Power 25W ERP
Antenna Diamond X-300 Fixed Base Station Vertical 5x5/8 @ 9dB
Antenna Height AGL 8 Metres or 27 Feet above ground level
Base of Mast ASL 284 Metres or 600 Feet above sea level
Repeater Controller Zetron 38
Duplexer Procom UHF duplexer - Model DPF70/6


The hardware is based on modified Nokia BSR450 UHF Repeater Base Station, transceiver & receiver comprise of separate modules & the PA Unit all enclosed within their own die cast housing, and the PA is directly mounted on the large rear heat-sink. The RF Power Output is 1 - 40 Watts on a continuous duty basis.

The Nokia BSR450 is supplied with an "N" Type connector for the transmitter, and a BNC connector for the receiver to allow easy connection to the diplexer or feeder cables. The rear panel includes a 9 and 25 way D sub connector that allow easy connection to external accessories such as other radios, control equipment or shared tone panel. All housed within one 4RU equipment cabinet.


Station Mode Duplex Base Station Repeater
Duplex Tx-Rx Frequency Separation 0.5 MHz Minimum
Antenna Impedance 50 ohms unbalanced
Duty Cycle Continuous
Temperatures -30’C to +80C


Transmit Frequency Output 439.5125 MHz
RF Power Output Minimum 1Watt Maximum 40Watts (Continuous Duty Cycle)
Frequency Deviation Wide-Band + or - 2.4KHz
Oscillation System Direct PLL Synthesizer System
Type of Crystal Unit TCXO
Frequency Stability + or - 0.0005% with Standard TCXO, + or - 0.0002
Frequency Response Within +1, -3db of 6db/octave pre-emphasis from 0.3 to 3kHz, 1khz reference
Signal to Noise Ratio More then 50dB at 1kHz 70% Modulation


Receive Frequency Input 430.5125 MHz
Receiver Type Double Conversion Super Heterodyne
Intermediate Frequency 1st IF 21.6MHz, 2nd IF 455kHz
Frequency Stability + or - 0.0005% with Standard TCXO, + or - 0.0002
Sensitivity Less than 0.5uV for 20dB noise quieting, Less than 0.35uV for 12dB SINAD
Squelch Sensitivity Less than 0.25uV
Modulation Acceptance + or - 7.0kHz
GB3OK Logic Controller


The Zetron Model 38A is a flexible repeater panel that provides individualized repeater service interface between BSR450 Repeater Base Stations

The Model 38A Logic controller providing all the functions that can easily be customized from 50 CTCSS encode/decode, repeat audio processing, Automatic morse code station identification , courtesy beeps and tail bips and all timers from PC from the front RS-232 9 way serial port.


Connections Rx audio, Tx key, CTCSS / DCS encode, Tx audio (mic), 12 VAC or DC power, ground. Optional carrier detect, alarm input and aux output.
Rx input Impedance 50 K? AC coupled. For connection to unsquelched discriminator audio.
CTCSS / DCS Level 0 to 4 Volts p-p. Impedance: Less than 1 K? AC coupled.
Transmitter Type Direct FM, or phase modulation. Flat or de-emphasized CTCSS encode.
Carrier Detect Internal noise detector or external carrier detect input. External input threshold adjustable 0 to 7 VDC.
Adjustments Four adjustments from rear panel: Rx input gain, CTCSS / DCS encode gain, Tx audio output gain, and carrier detect threshold.
Configuration Eight switches on rear panel: Rx audio gain high/low, repeat audio flat/de-emphasized, encode gain high/low, encode flat/de emphasized, tx audio gain high/low, COR source internal/external, COR polarity positive/negative, COR pull up on/off

Nokia BSR450 Repeater Base Station, Inside Out:

TX and RX Modules Transceiver & receiver comprise of separate modules all enclosed within their own die cast housing modules on the top side of the base station.
TX and RX Modules  
TX and RX Modules

Transmitter and receiver lids removed from the modules top left main double conversion super heterodyne receiver unit VCO/Direct PLL synthesizer system., on the right main transmitter unit VCO\Direct PLL synthesizer system and transmitter driver.

TX and RX Modules  
Logic Control Module Logic control module on the under side of the base station which is overall interconnections of transmitter, receiver and PA modules.
Logic Control Module  
PA and RX Module UHF 40 watt PA module comprise of separate modules enclosed within their own die cast housing at the rear of the base station.
PA and RX Module  
PA Module UHF continuous duty basis 40 watt PA module with lid removed from the module rear of the base station.
PA Module  
The Duplexer Procom Duplexer DPF70/6 is terminated with N-Type female connectors on Antenna, HI and LO jacks.

Frequency Range 406-470 MHz
Continuous Input power 50 watts
Insertion Loss TX-ANT and ANT-RX, <1,2dB
TX Noise Rejection >85dB
Duplex spacing DPF70/6-5/7 = 5-7 MHz

The Duplexer  
Low Noise Amplifier

The Low Noise Amplifier for 432 MHz band this special device and its unique circuit design it provides unequalled performance with weak signal.

Selective Gain 20 dB preamplifier included double helical band-pass filter with low noise figure and high gain

Low Noise Amplifier  
RMC Computer Generated Predicted Coverage
GB3OK Coverage
Colour Key   RMC Computer Generated Predicted Coverage
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