NHRC-4/M2 Repeater Controller
Installation Instructions
Rev. A Boards (shipped before January 1999)

These instructions will guide you in the installation and adjustment of the NHRC-4/M2 repeater controller.


  1. MASTR II Preparation
  2. Secondary Radio Port Wiring
  3. TS-32 Hookup
  4. Installing the NHRC-4/M2 in the MASTR II
  5. The LED status indicators
  6. Installing the NHRC-DAD Audio Delay
  7. Using the Digital Output
  8. Adjusting the Audio Levels

Board Layout
  1. MASTR II Preparation
    The NHRC-4/M2 operates using the MASTR II as the "primary" radio. The primary radio must operate in full-duplex mode. If your MASTR II is not already converted for full-duplex operation, consult the NHRC MASTR II infosite for duplexing information.

    There are two options for interfacing the CAS and TX audio to the controller. These signals do not normally appear on the the P908 plug on the system board of the MASTR II.

    Option 1: Use an interface cable

    Transmit audio and CAS appear on the controller at J1, a 3-pin header. Wire an interface cable as shown in the table below:

    J1 Connections
    Pin #
    1MIC HI
    J902 #6
    J904 #9
    3MIC LO
    J902 #5

    Option 2: Modify the MASTR II System Board.
    By cutting one trace and adding two wires to the MASTR II system board, the jumper described in option 1, above, can be avoided.

    Add a wire that connects P908 pin 2 to J902 pin 6 (the exciter's MIC HI input). Cut the trace that leads to P908 pin 3 on the system board, and add a wire that connects P908 pin 3 to J904 pin 9 (the CAS signal from the IFAS board). Install 0 ohm resistors (jumpers) R22 and R38 on the NHRC-4/M2 board, enabling the TX audio and CAS signals on the J908 connector. Note that these jumpers may already be populated on your board. If you plan on using the local microphone on the MASTR II's control head, install a 1.5K resistor in location R22.

  2. Secondary Radio Port Wiring
    The controller provides the secondary radio port on the F2 through F7 frequency select leads, using the P909 connector. In mobile MASTR II radios, these control lines are often subject to the installation of diodes and jumpers for sharing of channel elements on multiple channel selections. These diodes and jumpers must be removed from the system board for proper operation of the controller. Consult the MASTR II service manual for information on these jumpers.

    In base stations and repeaters, the P909 connector is unused. Individual wires must be attached to P909 to break out the secondary radio port.

    P909 Secondary Radio Port Connections
    Pin #
    Pin #

    It is extremely important that the radio attached to the secondary radio port be provided with a common ground from the MASTR II. The "A-" lead (J901 pin 30) is a good spot. If this common ground is not provided, erratic operation or distorted audio on the secondary radio will result.

  3. TS-32 hookup
    Connector JTS32 is a 5-pin header that allows the easy installation of an optional Communications Specialists TS-32 for CTCSS decode and encode. Wire JTS32 to the TS-32 as follows:

    JTS32 Connections
    Pin #
    1+V POWER
    5- GROUND &

    The TS-32 must have the JU-2 jumper cut. If you want to be able to disable the CTCSS requirement, install a switch on the HANGUP lead. The TS-32 will supply CTCSS encode tone to the exciter through the NHRC-4/M2.

    Adjust the CTCSS deviation with the R29 on the TS-32 board, with the "CG LEVEL" pot on the MASTR II exciter set to midrange. The ideal deviation for the CTCSS tone is 750 Hz.

    Consult the TS-32 INSTRUCTION SHEET for details on setting the CTCSS frequency.

  4. Installing the NHRC-4/M2 into the MASTR II
    The controller installs in the MASTR II where the MASTR II "Channel Guard" board normally belongs, plugged into the top of the systems board in the front of the radio. If you have not already removed the Channel Guard board, do so now by pulling it straight up and out of the radio. The NHRC-4/M2 installs with the component side of the board facing the control head cable connector. Carefully line up the P908 (left side) and P909 (right side) connectors with the pins on the system board. Push the board down firmly until the connectors are right against the system board. The controller is now installed.

  5. The LED Status Indicators
    The NHRC-4 repeater controller is equipped with five status LEDS that aid in setup and troubleshooting. There are green LEDs for each radio port that indicate that the controller has getting a valid CAS (carrier operated switch) and, if a CTCSS decoder is connected, a a valid CTCSS decode signal. The appropriate green LED should light when itsreceiver is active, and, if a CTCSS decoder is present, the correct CTCSS tone is present. The yellow LED indicates that a DTMF signal is being decoded on the primary receiver. This LED should light for the entire duration that the DTMF signal is present on the primary receiver. The red LEDs indicates transmit. These LED will light when its respective transmitter is transmitting.

    The LEDS can be disabled to reduce the power consumption of the controller. Remove jumper JP2 to disable the LEDS.

  6. Installing the NHRC-DAD with the NHRC-4/M2
    J-2 Primary Radio DAD
    J-3 Secondary Radio DAD
    1+13.8 Volts to delay board
    2Audio to delay board
    3Audio from delay board
    4Ground/Audio Return

    The audio delay for the primary radio simply plugs in to J2. The audio delay for the secondary radio plugs in to J3. If the audio delay is not installed, a jumper between pins 2 and 3 of the port's delay connector must be installed, or the controller will not pass audio.

  7. Using the Digital Output
    The NHRC-4 Repeater Controller has a digital output that can be used for various remote control applications or to control a fan on the repeater's transmitter. The digital output is an open-drain into a power MOSFET, which is capable of sinking quite a bit of current, but we recommend a maximum load of about 500 mA. Use a relay to drive larger loads. The open-drain output can be used to gate the HOOKSWITCH signal to a TS-32 or other CTCSS decoder, to enable or disable CTCSS. Software allows the output to be enabled, disabled, or pulsed. In fan control mode, this output will be turned on when the transmitter is turned on, and turned off a programmable amount of time after the transmitter is turned off.

  8. Adjusting the Audio Levels
    Audio Level Adjustments
    VR1Primary Receiver Level
    VR2Secondary Receiver Mix Level
    VR3Primary Receiver Mix Level
    VR4Beep Tone Mix Level
    VR5Primary Transmitter Master Level
    VR6Secondary Transmitter Master Level

    Preset all potentiometers to midrange. Key a radio on the primary input frequency, send some touch-tones, and adjust VR1 (the primary receiver level) until DTMF decoding is reliably indicated by yellow LED D5.

    The primary radio's transmit deviation is set with VR5 (the primary transmitter master level) on the controller board and the transmitter's deviation/modulation control. The key to properly adjusting these controls is to remember that the limiter in the tranmitter is after VR5 but probably before the transmitter's deviation/modulation control. The transmitter's deviation/modulation control will set the actual peak deviation, and VR5 will set the level into the transmitter. You do not want excessive limiting on normal speech going through the repeater; it sounds bad and tends to "pump-up" background noise. On the other hand, some limiting is desirable. An oscilloscope connected to the audio output of a receiver tuned to the transmitter's frequency will show limiting as the audio gets "flat-topped" or clipped by the limiter. Ideally, a 4.5KHz deviation signal input to the repeater should result in a 4.5 KHz deviation output, and 5.5 KHz of input deviation should result in just under 5.0 KHz of deviation out of the repeater. A service monitor (or two), deviation meter, and/or a signal generator are necessary to do this job right.

    The secondary radio's transmit deviation is set with VR2 (the secondary transmitter master level). Enable the secondary transmitter, and adjust VR2 for proper transmit deviation, similarly to VR5.

    Enable the secondary receiver, and adjust VR6 for reasonable deviation on the enabled transmitters when a signal is received on the secondary receiver.

    Adjust VR4 (the beep level) to set the courtesy tone and CW tone level.

    VR3 is used to set the primary receiver's audio mix level, and may not need to be adjusted from midpoint.

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