NHRC-4/M2 Repeater Controller
Installation Instructions
Rev. B Boards (shipped after 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/TS-64 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 R38.

  2. Secondary Radio Port Wiring
    The controller provides the secondary radio port on the F3 through F8 frequency select leads, using the P909 connector. These leads are routed to the front panel control cable connector on the systems board. In mobile MASTR II radios, these control lines are sometimes subject to the installation of diodes and jumpers and cutting of traces to share channel elements across more than one channel selection. These diodes and jumpers must be removed, and the cut traces must be jumpered to for proper operation of the controller. Consult the MASTR II service manual for information on these jumpers.

    Dissecting an old control cable makes an easy job of attaching your secondary radio to the MASTR II. In an E-chassis MASTR II, a bit of clever wiring in the systems board can allow a repeater on the "top deck" and the secondary, remote-base radio on the "bottom deck".

    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 #
    J901 (control cable)
    Pin #
    1Secondary port CASF815
    2Secondary port PTTF714
    3Secondary port CTCSS detectF613
    4Secondary port receiver audioF512
    5Secondary port transmitter audioF411
    6Digital outputF310
    7no connectionF29
    8Unused, grounded to select F1F18

    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/TS-64 hookup
    Connector JTS32 is a 7-pin header that allows the easy installation of an optional Communications Specialists TS-32 or TS-64 for CTCSS decode, encode, CTCSS audio filtering, and reverse-burst. (Reverse burst is only available with the TS-64.) Wire JTS32 to the TS-32/TS-64 as follows:

    JTS32 Connections
    Pin #
    1 +V POWER +10 volts to CTCSS board
    2 CTCSS DECODER INPUT receiver audio to CTCSS decoder
    3 TO AUDIO FILTER INPUT receiver audio to audio filter input
    (separate lead for TS-64)
    4 FROM AUDIO FILTER OUTPUT filtered audio to controller
    5 CTCSS DETECT decode signal from CTCSS decoder
    See important warning below!
    6 CTCSS ENCODER OUTPUT CTCSS tone to transmitter
    7 - GROUND & HANG-UP Ground.

    This input is pulled low by the CTCSS decoder when CTCSS is NOT PRESENT.
    It will float high when CTCSS is detected.
    Application of voltage to this input will destroy Q4 and render the controller inoperative.
    Damage of this nature is not covered by the NHRC Limited Warranty.

    The TS-32 and the TS-64 both have a high-pass filter to remove the CTCSS tone from the repeated audio. By removing jumper JP3, the controller's audio can be passed through the audio filter on the TS-32/TS-64.

    Note: If the audio filter is not used, then jumper JP3 must be installed in order for audio to be passed through the controller.

    The Communications Specialists CTCSS boards are not supplied by NHRC. Contact Communications Specialists at 800-854-0547 directly to order these boards.

    TS-64 Notes

    Consult the NHRC-4/M2 TS-64 Application note for detailed connection instructions.

    The TS-64 has a reverse-burst/PTT delay feature that can be used with the NHRC-4/M2. This feature is useful to eliminate the squelch crash received by the user's radio when the repeater transmitter drops. Note that the user's radios must have CTCSS decoding enabled for this to work. The NHRC-4/M2 provides support for the PTT delay through jumper JP4. JP4 pin 1 is the controller's PTT signal, and JP4 pin 2 is PTT to the MASTR II. If the reverse-burst/PTT delay feature is not used, then a jumper must be installed on JP4 so the controller can key the MASTR II.

    Adjust the CTCSS deviation with R20 on the TS-64 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-64 INSTRUCTION SHEET for details on setting the CTCSS frequency and the reverse burst.

    TS-32 Notes

    The TS-32 must have the JU-2 jumper cut. Use the OUT-2 signal from the TS-32 into the CTCSS detect of the NHRC-4/M2. 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.

    It is strongly recommended that the CTCSS filter be used, as described above, if both CTCSS encode/decode and the audio delay are used.

    See the Operation Instructions section on programming the flag bits to tell the controller the delay is present.

  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.

    Note: If VR1 is set too high, a crackling noise may be heard in the transmitted audio during the hang time. Reduce the level set by VR1 until this noise goes away. Any repeated audio level reduction caused by adjusting VR1 can be compensated for by adjusting VR3 (primary receiver level) or VR5 (primary transmitter output level.)

    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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