gb3naChannel : RV53
Repeater Output : 145.6125 MHz
Repeater Input : 145.0125 MHz
CTCSS : B-71.9Hz
Locator : IO93HO
Echolink : N/A
Coverage map : click here
Latitude/Longitude: 53.585743 / -1.358101


GB3NA was updated in April 1999 to replace the ageing Storno 9000 repeater that has been in use for the past 10 years.

The repeater GB3NA is the first one of three to be upgraded. The site where GB3NA is located has a harsh RF environment. The receiver is designed for outstanding performance. With 7 large helical filters in the front end and 12 poles of IF filtering the receiver is immune to desense at interference levels greater than 75,000 uV. Two of the resonators are placed ahead of the RF pre-amplifier for exceptional overload resistance. The 21.4 MHz first IF and shielded oscillator/multiplier chain make it difficult to even measure an image, and its double-balanced first and second mixers reject intermodulation products by 80 dB. Feedback, damped-Q tuned circuits and de-coupling are used so that gain stages operate conservatively – not wide open. NPO and mylar capacitors keep the performance consistently high over temperature extremes.

The receiver’s operational features: automatic fast/slow squelch to lock in on weak signals and virtually eliminate squelch tails on strong signals. Full metering provisions for signal strength, deviation, and discriminator are available.


The Receivers

Frequency: 145.0125 MHz.
Sensitivity: .25 – .35uV (typ.) for 12dB SINAD.
Selectivity: -105dB at +15KHz.
Spurious response: -85dB and Image response -125dB Image.
Overload/Desense: 75,000uV + 600KHZ.
Intermodulation: -80dB (EIA method).
I.F. 21.4MHz first, 455KHz second.
I.F. Filtering 8-pole crystal at 21.4MHZ 4-pole ceramic at 455KHz.
First oscillator stability: +.0005% (-10 to + 60C).
Squelch Circuit Schmitt trigger with 6dB hysteresis.
Squelch Threshold: .1-.15uV, automatic switch to fast mode with signals greater than 10uV.
Modulation acceptance: + 7KHz.
Audio de-emphasis: -6dB/octave (EIA).
Audio out 1.5W into 4ohms (local) 0.4Vrms,1000ohms (line/repeat).
Logic output open collector, selectable active high or low.
Voltage required 13VDC nominal (11-14VDC limit).
Current Drain 250mA with full audio output 200mA nominal unsquelched, 180mA squelched.
Crystal specification 136-151MHz Fx = (Fo-21.4MHz) Parallel resonant, third overtone resistance 30ohms max. 12pF load capacity, HC-25/U case.
Physical (modular version) 5″ x 7.25″ x 2.5″ enclosure w/feedthru capacitors and N type UHF connector.

The Logic – G8CUL

The logic itself is a relatively complex piece of electronic design, with a processor containing its own control programme, custom designed for use on all three repeaters.


The Repeater Logic has been designed to provide many features for the control logic of the repeater. Nearly all these features can have their parameters individually programmed and set-up using a normal PC. To avoid all the previously configured parameters being forgotten when the power is removed, an EEPROM device is used to store them. The control logic is controlled by a microcomputer system which operates the repeater itself, as well as controlling many of the operating parameters of the repeater.

System Description

In its simplest form, the logic only requires 5 connections.
These are:

Audio in from the repeater receiver.
Squelch in from the repeater receiver.
Audio to the repeater transmitter.
PTT to the repeater transmitter.
The audio signal from the repeater receiver must have its de-emphasis removed, otherwise the incoming CTCSS low frequency tone will be enhanced by the de-emphasis circuitry. Likewise the repeater transmitter must have its pre-emphasis removed otherwise the outgoing CTCSS low frequency tone will be removed. The through audio tailoring is thus ‘neutral’, with the transmitted audio being the same as that received (within the audio pass band of 300 – 3500Hz).

Audio in from the receiver is split to all devices that need it.
They are:

CTCSS tone detector and generator.
‘Normal’ 1750Hz tone burst detection.
DTMF tone detector.
Computer data to the MODEM.
The squelch line in from the receiver is also used by the processing system. The processor control programme detects the squelch opening and – if a valid CTCSS tone or tone burst is detected – operates the PTT signal to the transmitter, and feeds the incoming audio to the transmitter input. Note that at present, the CTCSS on receive is only used for initial access in a similar way to a tone burst. Once accessed, no further tone (or tone burst) is required to keep the repeater open. The outgoing CTCSS is however, used in a continuous mode (if enabled), except when the repeater is giving its callsign on shutdown or beacon, although the CTCSS may be enabled even for these callsigns if required.

The CTCSS device itself is interesting, and deserves a bit more explanation. Any incoming CTCSS tone is filtered and detected, and the processor is then informed what the actual received tone frequency is. The processor can then decide if it is the correct tone or not, and act accordingly. The through audio is also filtered by the CTCSS device to remove any incoming tone, and an internal audio switch can be used to control the audio input to the transmitter. The transmit tone is generated independently to the receive detection, thus making the device suitable for repeater operation. The CTCSS device therefore has two outputs, through audio and CTCSS tone. Both of these are mixed together with the outputs from the tone oscillator and computer control MODEM before being peak clipped and finally filtered ready for the transmitter input.

Other facilities include the control of a second receiver/transmitter combination which may be used for remote control on a different frequency (or even band) to that of the repeater itself. Control signals are also provided for the synthesised voice unit as well as inputs for repeater linking. The control programme built into the repeater logic contains many commands to allow the simple control of all the parameters that can be varied.


Power requirements: +8 to +20V DC at about 100 mA. Normal or Standby power input. Audio input: 300 – 400 mV P:P (adjustable) into 10k* composite signal.
Through audio (reference):
CTCSS at * -16 dB,
Tone burst at -6 dB,
DTMF at -6 dB,
Data tones at 0 dB.
Audio output: * 0.5V rms. into 1k*, (adjustable) composite signal. Through audio (reference):
CTCSS at * -16 dB, Ack/callsign tone at -6 dB (high) -16 dB (low),Data tones at 0 dB.
Squelch input 5V logic signal, either polarity (other voltage levels possible).
PTT output Diode protected open collector output, 100 mA max. (ON), 25V max. (OFF).
Control 9 pin RS232 connector for direct connection to PC for logic set-up and fine-tuning. Data tone decoder/encoder for limited ‘on-air’ control. N.B., the DTMF and data signals can be linked to a separate RX/TX combination if required.
Shutdown: Local (via switch) or remote (DTMF or computer data).
Voice Control signals to and audio input from external synthesised voice unit (Maplin board).
Repeater linking: Extra squelch and audio input for second (link) receiver.
Configuration: All configurable parameters held in non-volatile EEPROM for easy modification via built-in serial port.

Temperature Range: Standard 0 C to 50 C, Extended -20 C to 50 C.

Operational Characteristics

To provide simple control and versatility for a wide variety of uses, a 128 byte EEPROM is included to store all the configuration data which give the repeater its characteristics.
These data include the following:-

DTMF tone sequence for shutdown/start-up.
Beacon time.
Option selection.
Various timings etc.
All modifiable features are stored in the EEPROM, so are relatively easy to change. All features are accessible via a direct connection to the logic board itself (RS232), some may also be changed ‘on-air’ while the repeater is operational by using the datalink and a ‘BayComm’ modem. These latter changes are only simple ones, and do not affect the fundamental operation of the repeater. All modifiable features are controlled by a set of simple commands via the built-in RS232 serial port. A normal PC is suitable for this control.


During normal use, the Repeater Logic gives the repeater the normal repeater characteristics. The intention is to provide a control system which makes the repeater simple for users to operate through, yet versatile for set-up purposes. All the normal features are available; tone burst minimum length, input carrier minimum length before the repeater will stay up, etc. Long over time-out is also provided if required. If this is enabled, the repeater will shut off the incoming audio if required, replacing it with the normal time-out ‘pips’.

This stage of time-out can also be set to eventually time-out itself, when the repeater will give its callsign and shutdown. In this situation, when the incoming signal eventually goes away, the repeater transmitter will briefly come on, and send ‘OK’ on CW, to inform all the bored listeners that the talkative operator has finally let go his/her PTT! During the normal time-out ‘pip’ phase, the time-out may be reset, and the incoming audio re-enabled, by a tone burst of the correct length detected on the input. This signal will, of course, have to be stronger than the ‘timed-out’ signal.


The hardware design is based around a single-chip micro-controller from Motorola, the MC68HC705. This device contains up to 32 Input/Output lines, a timer, a serial port, RAM and about 7k bytes of EPROM to contain the programme. The processor is interfaced to other devices within the circuit design to provide the required functions. Other features incorporated are implemented by the usual NE567 for tone burst detection, an FX805 for CTCSS, MT8870 for DTMF decoding and TCM3105 for serial data input and output. Non-volatile parameter storage is provided by a 128byte EEPROM.

Analogue Sheet

Incoming audio from the receiver is amplified by one half of a IC (TLC272). This signal is then split to feed all the devices which require it. To a NE567 tone burst detector, MV8870 DTMF decoder and a TCM3105 data decoder. The remote control signals to may be routed from a separate receiver. The received audio signal is also fed to an FX805, for the audio path and the CTCSS tone, a 300Hz high pass filter to remove the incoming CTCSS tone.

The audio is then added to the outgoing CTCSS tone as well as all other outgoing audio signals. This outgoing information consists of through audio, CTCSS transmit tone (generated by the FX805), CW ident and data tones. This combined audio is then peak clipped to guard against over-deviation of the transmitted signal, and filtered by a 40dB per decade low-pass filter (IC20). The output of this filter is fed to the repeater transmitter.

No de-emphasis or pre-emphasis is included in the logic. In fact, the repeater transmitter must have its pre-emphasis removed to avoid attenuation of the outgoing CTCSS tone. Likewise on receive, any de-emphasis in the repeater receiver must also be removed, to give neutral audio tailoring and avoid excessive received CTCSS amplitude. The overall effect of not having any in-built audio tailoring is that signals are transmitted as they are received, with the exception of the peak clipping and subsequent low pass filtering.

The tone burst detect frequency is set and has a nominal bandwidth of about 100Hz.

When MT8870 detects a valid DTMF tone it produces an interrupt signal to the processor, and puts the DTMF tone binary code on its output for the processor to read. A TCM3105, detects the standard Bell 202 tones, producing the decoded serial data into the processor serial input. The serial output from the processor is routed to which gives either a 1200Hz or 2200Hz tone on its analogue output which is switched on and off into the transmitter input under processor control.

The ‘ack’ and CW ident tones are produced by the usual phase shift oscillator, buffers the oscillator output, is used to vary the gain under processor control, which has the effect of stopping and starting the oscillating action. The tone output level can be switched between a high and low level, (depending upon input signal presence) The tone frequency is set to a nominal 1700Hz .

At the heart of the logic is the micro-controller, or processor – a MC68HC705C8. This contains all the usual micro-processor hardware elements, CPU, clock, timer, I/O, EPROM (for the control programme), RAM, and serial interface. All these features are used by the control programme. Two squelch signals are buffered by 74HCT14, and fed to the processor. These are for the main and (optional) auxiliary receivers. Another squelch input is available for an extra link receiver, which may be used for repeater linking. An extra audio input to the transmitter summing amplifier is also provided for link receiver use (or synthesised voice).

The RS232 interface is connected via PL1, a 9 pin ‘D’ type, via the RS232 interface device, an LT1080, to the serial in and out of the processor. These signals are fed via 2 ‘gates’ of an analogue multiplexer – 74HCT4053. This allows the serial input and output of the processor to be switched between the RS232 interface and the MODEM IC. The control for this switching is also applied to the processor so the control programme can ‘know’ when LK1 is removed for set-up. It generates its own ?10V (not exact figure) for the RS232 interface levels by a simple internal charge-pump system. Outputs to the two PTT signals, for the main and (optional) auxiliary transmitters, is via open collector transistors to operate conventional PTT type controls. These signals also drive two LED’s – LED3 and LED4, via two inverters to give an indication when the transmitter(s) are on.

The repeater may be shut down by the remote commands.

Incoming power at a nominal +12V is applied to a regulator, from either the main power, or battery back-up. The application of +12V on the main power is used to select the main or backup ‘ack’ character. If a battery supply system is used, this facility will give indication of mains failure. Power for the analogue circuitry, at ?5V is generated by a NMA0505S, which is a low power isolating switching power converter. Inputs and output are filtered to reduce interference from the digital to the analogue circuitry.

XLS93C46P, is a 128byte EEPROM connected to the processor by a serial data link. The DATA_OUT and SER_CLK signals are shared by the CTCSS IC, each having separate Chip Select (CS) and DATA_IN signals. All of the configuration data is held in this EEPROM, which does not forget its contents when power is switched off.

The Transmitters

MODULATION is accomplished by true FM. A variable gain cell amplifier is used for low distortion audio without clipping (less than 2%). Compression begins at 4.8 KHz and hard limiting will occur at a level of 5 KHz. In hard limiting the modulation is held constant for input levels of greater than 30 dB. Unlike most transmitters today, the transmitter uses a MOS FET for the final transistor. The MOS FET has a much lower noise floor ( typically 3 times lower ) and is not subject to thermal runaway as bipolars are. The MOS FET used in this transmitter is capable of withstanding up to a 30:1VSWR. When configured for high power operation, the transmitter is supplied with a multiple section lowpass filter to suppress harmonics.

Power Supply voltages are decoupled in all stages to prevent noise pickup using ferrite beads for high frequency and capacitors for low frequency rejection. The circuit board also has copper ground planes on the top and bottom with multiple feed through points for excellent R.F. grounding. The receiver is mounted in an R.F. tight enclosure with feed-through capacitors for both audio and power supply lines. The R.F. out is supplied to an N type UHF connector.

Frequency: 145.6125 MHz.
Power Output at 24V High Power 30 Watts @13.8V High Power 15 Watts. We run 14DBW.
Crystal Multiplication 12x.
Frequency Control: Parallel resonate crystal (22 pf load capacitance, HC-25/U holder. Proportional oven used in FCC type accepted units.
Output Amplifier: MOS FET capable of withstanding 30:1 VSWR.
Modulation: Direct FM. Variable gain cell amplifier for audio compression and limiting with low distortion. Adjustable from 0-7 KHz.
Frequency Stability: +/-.0005% (-30c to 60c) +/- .0001% with optional proportional oven.
Harmonic Output: Greater than 65 dB below rated output.
Spurious Output: Greater than 90 dB below rated output.
Noise Output: Greater than 90 dB below rated output in high power mode at 600 KHz from output

Audio Response: Within +2/-3 dB of EIS standard 6 dB/octave pre-emphasis from 300 Hz to 2700 Hz. Less than 2% distortion.
Duty Cycle: Continuous.
Emission Designator: 5F3.

ProComm 6 cavity VHF purpose built giving 92.5db isolation.
Feeder cables

11 meters Westlake W150.

1 W300 Watson antenna to give a 6.5db. Waters and Stanton
Power Supplies

30 Amp 13,8V solid state.
10 Amp 24 Volt solid state.

Remote Control

The MoTron AK-16 DTMF Controller Board is used for the remote control operation of the repeater GB3NA and is capable of remotely operating 16 perimeters. It has 16 relay driver outputs. The AK-16 can address all 256 house/unit codes. The AK-16’s 0-12 digit security code and CW ID are easily programmed (or re-programmed) using your DTMF keypad! Five modes of operation allow various combinations of real-time control, on/off/momentary output control, and CW response tones. For relay control, the AK-16 can easily be mated to either the RB-16/10 or RB-8/10 via ribbon cable. Additional features include CW report back when relay status is polled, a watch-dog timer reset, and a serial output that converts incoming DTMF to ASCII for input into your computer.

Fingerprint Hardware and Software

The MoTron TxID? Transmitter FingerPrinting System fitted to GB3NA, identifies individual transmitters using a patented technique based on the principle that carrier operated radio transmitters exhibit a unique frequency versus time start-up characteristic before stabilizing on the operating frequency. Carrier operated radio transmitters exhibit a unique frequency versus time start-up characteristic before stabilising on the operating frequency – even radios of the same make and model. This ‘FingerPrint’ can be captured, stored and analysed. Our exclusive TxID? Software, which can automatically match and compare up to 256 FingerPrints, and the patented technology of the TxID-1? IBM/Compatible circuit board will help us to identify the abusers on the repeater. An onboard fast squelch starts the FingerPrinting process. The voltage on the receiver’s discriminator is sampled, digitised and stored. The leading edge of the carrier is then captured, stored and displayed. Other information about the signal is also captured, including DTMF, CTCSS and DCS signals with separate peak deviation readings, and displayed with the FingerPrint. The TxID? System can optionally control a tape recorder, capturing all or part of the transmission on audio tape along with the digitally encoded FingerPrint data. Deviation measurements and Spectrum Occupancy features further enhance the system. The TxID? System works with the Receiver, the TxID-1? can also capture the frequency of operation, as well as set the frequency.

Bandpass Filter

DCI Communications Ltd 2Mhz Bandpass filter.

The DCI-145-2H (144-146 MHz) has a 2MHz filter fitted with silver “N” Type connectors.
Passband: 144 to 146 MHz
Passband Loss: less than 1dB
Selectivity: -68 dB at 135 MHz -55 dB at 155 MHz
Power Rating: 200 watts
VSWR: 1.3:1
Connectors: SO-239 silver-Teflon?
Dimensions: 12″ x 3″ x 5″
Weight: 2 lb. 11 oz.

3 comments on “GB3NA
  1. D J Long says:

    Is this the repeater on R3 that is being abused on 2m ?
    What I am in search of is a station that stays open with hum and White noise? through it.
    You MAY being deliberetly abused because sometimes where I am on the side of the M2 there is a blank carrier on the input which has “vehicle” QSB on it.
    Never the less the presence of this racket stopping the scan it getting a nuisence!
    All the best

  2. 2E0BLF says:

    I think what you are possibly hearing is GMSK data from GB7YD.

  3. kay says:

    I know this is an old post but I don’t think you will be receiving GB3NA at the side of the M2. GB3NA has good coverage, but don’t think it’s THAT good!!

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