NHRC-4 Repeater Controller
Installation Instructions

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


  1. Electrical Connections
  2. The LED status indicators
  3. TS-32 Hookup
  4. Installing the Audio Delay
  5. The Digital Output
  6. Adjusting the Audio Levels

Board Layout
  1. Electrical Connections
    The controller uses a 8 pin .100 header for all the primary radio's signals and DC power, a 6 pin .100 header for the secondary radio's signals, and a 6 pin .100 header for an external TS-32 CTCSS encoder/decoder for the promary radio. In addition, it has two 4 pin .100 connectors to support optional NHRC-DAD digital audio delays for both radio ports.

    Each radio port requires audio and a signal present indication (CAS) from it's receiver, and supplies transmit audio and PTT to it's transmitter. The controller requires 13.8 volts DC for power, which is provided on the primary radio's connector.. Be very careful when wiring DC power to the controller, reverse polarity will severely damage the controller. The connector pinouts are shown in the tables below.

    J-1 Primary Radio Port
    1+13.8 Volts
    2CAS (active high)
    3PTT (active low)
    4Receiver Audio
    5Transmitter Audio
    6Fan/Digital output (active low)
    7Ground/Audio Return
    8Ground/Audio Return

    J-2 Secondary Radio Port
    1CAS (active high)
    2PTT (active low)
    3CTCSS detect (active high)
    4Receiver Audio
    5Transmitter Audio
    6Ground/Audio Return

    J-3 Primary Radio Port TS-32 Connector
    PinUseTS-32 Signal
    1+13.8 Volts to TS-32+V POWER
    2Receiver AudioDECODER INPUT
    3Receiver AudioAUDIO FILTER INPUT
    4Filtered AudioAUDIO FILTER OUTPUT
    5CTCSS DetectOUT-2
    6Ground/Audio Return- GROUND & HANGUP

    J-4 Primary Radio DAD
    ("MN DLY ")
    J-5 Secondary Radio DAD
    ("RB DLY ")
    1+13.8 Volts to delay board
    2Audio to delay board
    3Audio from delay board
    4Ground/Audio Return

    Receiver audio can typically be taken from the high side of the squelch control. This audio must be de-emphasized with the controller's de-emphasis circuit, which provides a -6dB/octave slope. Optionally, audio can be taken from later in the receiver's audio chain, where it is already de-emphasized. Care must be taken that this source of audio is not subject to adjustment by the radio's volume control. If the receiver audio has not been properly de-emphasized, either in the receiver itself or on the controller board, the repeater will have a very "tinny", unnatural sound to it. The NHRC-4 repeater controller is shipped without the de-emphasis circuit populated on the printed circuit board, for "flat" audio response. To install the deemphasis filter, two 100K ohm resistors must be removed, and a 51K ohm, a 510K ohm, and a .0068 microfarad capacitor must be installed on the board. Consult the NHRC-4 Repeater Controller (Audio) schematic for modification instructions.

    The receiver must provide a signal present indication (also called CAS, COR, RUS) to the controller. The controller requires an "active-high" signal here. If your radio only has "active-low" signalling available, a simple inverter can be constructed with a 2N3906 and a 4.7K resistor. Connect the emitter of the transistor to a source of positive voltage, the collector to the controller's CAS terminal, and the base to the active-low signal through the 4.7K resistor.

    Transmitter audio can be fed directly into the microphone input of the transmitter. VR5 is the master level control for the primary radio, used to set the audio level into the transmitter. VR2 is the master level control for the secondary radio. The transmitter's deviation limiter (sometimes called IDC) should be set such that the transmitter cannot overdeviate, regardless of input signal level. One way to adjust transmitter deviation is to set the transmitter deviation limiter wide open (unlimited), adjust the controller's master output until the transmitter is slightly overdeviating, then set the transmitter's deviation limiter to limit just below 5 KHz deviation. Then reduce the controller's master output until the transmitted audio does not sound compressed or clipped. Transmitter deviation should be adjusted with a service monitor or deviation meter.

    Transmitter keying is provided by a power MOSFET (Q2/Q6) configured in an open-drain circuit. This can be used to key many transmitters directly. The MOSFET essentially provides a closure to ground for PTT. For other transmitters, the MOSFET can drive a small relay to key the radio. Although this MOSFET can handle several amps, we recommend that no more than 500 mA of current be drawn through it.

  2. 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. This LED should light when the repeater's receiver is active, and, if a CTCSS decoder is present, that 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 the each transmitter is transmitting.

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

  3. TS-32 hookup
    Connector J3 is 6-pin header that allows the easy installation of an optional Communications Specialists TS-32 for CTCSS decode and possibly encode. Consult table J-3 "Primary Radio Port TS-32 Connector ("TS-32")" for hookup information.

    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, or you could wire the HANGUP lead to the J1 Fan/Digital Output pin to allow remote enable/disable of the CTCSS requirement. If you like, you can wire the TS-32's ENCODE OUT pin into your transmitter's CTCSS input to encode PL on the repeater's output.

    The TS-32 is normally configured with it's high-pass filter in-circuit to remove received CTCSS tones. Jumper JP1 on the controller board must be removed when the TS-32 high-pass filter is used. If the TS-32 is not installed, then jumper JP1 must be installed in order for audio to pass through the controller.

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

  4. Installing the Audio Delay
    The audio delay for the primary radio simply plugs in to J4. The audio delay for the secondary radio plugs in to J5. 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.

  5. 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. 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.

  6. Adjusting the Audio Levels
    Audio Level Adjustments
    VR1Secondary Receiver Mix Level
    VR2Secondary Transmitter Master Level
    VR3Primary Receiver Mix Level
    VR4Primary Receiver Level
    VR5Primary Transmitter Master Level
    VR6Beep Tone Mix Level

    Preset all potentiometers to midrange. Key a radio on the primary input frequency, send some touch-tones, and adjust VR4 (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 VR2 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 VR1 for reasonable deviation on the enabled transmitters when a signal is received on the secondary receiver.

    Adjust VR6 (the beep level) to set the courtesy tone and CW tone level.

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

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/nhrc-4/installation.php, version 1.02, last modified 02 January 2005 12:20
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