Uild the NHRC Linking Repeater Controller

,..AjuI gel with The program.

Jeff Otterson N1KD0 3543 Tritt Springs Way Marietta GA 30062

Peter Gailunas KA10KQ 444 Micol Road Pembroke NH 03275

Rich Cox N1LTL 452 Brown Road Candia NH 0303^

The unexpected success of our earlier repeater controller project ("Build a $60 Talking Repeater Controller," QST. February 1997), including user feedback, prompted us to design another low-cost controller project. NHRC-2 users wanted another simple repeater controller with linking capability. We thought about their requests for a while, and then we designed this project: the NHRC-4 Linking Repeater Controller. You'll find information about kits and assembled and tested units at the end of this article.

The NHRC-4 controller will easily integrate to any repeater. It has two radio ports: primary and secondary. The primary port supports a normal full-duplex repeater, while the secondary one can be used for a remote base, a link radio, or a "slave* repeater.

The controller supports all the standard controller features: CW ID. courtesy tones, and timers for Lhe ID; "hang" or "tail" tinier; and an individual timeout timer lor each port* The

28 73 Amateur Radio Today * September 19

CW messages, timer values, and other parameters are all programmed over the air with DTMF command sequences. The controller has LED indicators for PTT and CAS for each port, and a DTMF indicator for the primary port. There are expansion connectors for both ports to support external digital delay boards, which can eliminate squelch tails and the leading edge of DTMF sequences.

Each port can have a distinct courtesy tone to indicate to repeater users which receivers are active. There are five different events that can trigger a courtesy tone, and each tone can be programmed independently. The live events are: the primary port's receiver dropping; the primary port's receiver dropping while the secondarv port s receiver is active and "alert mode is selected; the primary port's receiver dropping when the secondary port s transmitter is enabled; the secondary m port's Deceiver dropping; and the secondary ports receiver dropping when the secondary port's transmitter is enabled.

There are lour different modes for the secondary porL The secondary port can be off, where nothing is received, transmitted, or otherwise indicated from the secondary port. It can be in "alert mode," where activity on its receiver is indicated by a distinctive courtesy tone on when the primary port s receiver drops. (This mode is particular I \ useful in the remote-base environment to indicate channel activity without having to actually listen to the channel activity on the remote base ) The secondary port can also be in "monitor mode." where its receiver audio is transmitted over the primary port's transmitter. A unique courtesy tone indicates that the repeated signal originated from the secondary port. The fourth mode is the "transmit" mode, where the secondarv port transmits the signal received on the primarv port's receiver, and the primary port's transmitter repeats both the primary and secondary port's audio.

The secondary port's PTT (push-to-lalk) signal can he programmed to follow the primary port's C AS {carrier-activated switch) signal, or the primary port's PTT signal. Following the CAS signal is typical for remote base and linking applications, and following the primary port's PTT signal is typical for a slave repeater

The controller also has one digital control output. This output can be turned on or off or he pulsed by DTM i-remotc control, or the output can be configured to operate a transmitter fan. which will be turned on when the transmitter is turned on, and run for a programmable amount of time after ihe transmitter turns off.

Circuit description

The controller's circuitry is quile simple, consisting of some digital level conversion networks for Ihe CAS and ITT interfaces, audio mixing and gating, and DTMF reception, all orchestrated by a Microchip PIC 16F84 microcontroller. The 16F84 manages all controller functions. It provides internal EEPRGM to store the controller's program, as well as the user-programmabte CW messages, timer values, and so forth, and RAM for ihe program's operating variables,

DTMF is decoded by a Tci-Tonc M8870 DTMF receiver, which also supplies the 16F84 with a clock signal. A quad op amp. a voltage regulator, and a handful of discrete components round out the design.

The circuit alone would do nothing without the custom software programmed into the 16F84. The control program contains approximately 9tH) instructions. The software provides all the logic, and generates the timers and programmable courtesy tones for the controller*

Electrical connections

The controller uses an eight-pin. 0.100 header for all ihe primary radio's signals and DC power; a six-pin, 0. \ 00 header for the secondary radio's signals; and a six-pin. 0.100 header for an external TS-32 CTCSS encoder/decoder for the primary radio. In addition, it has two four-pin, 0.100 connectors to support optional NHRC-DAD digital audio delays for both radio pons.

i^ach radio port requires audio and a signal present indication (CAS) from its receiver, and supplies transmit audio and P IT to its transmitter. The controller requires 13.8 VDC for power, which is provided on the primary radios connector (Be very careful when wiring DC power to the controller-reverse polarity will severely damage the controller.)

Receiver audio can typically be taken from the high side of the squelch control. This audio must be de-cmpha-sized with ihe controller's de-emphasis circuit, which provides a -6 dB/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 can be built with a de-emphasis circuit populated on the printed circuit board, for "flat" audio response. To insiall ihe de-emphasis filter, two 100 k resistors must be removed, and 51 k and 510 k resistors added, as well as a .0068 |iR Consult the NHRC-4 Repealer 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" signaling available, a simple inverter can be constructed with a 2N3906 and a 4.7 k 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 4,7 k resistor.

Transmitter audio can be led 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 Iimiter (sometimes called IDC) should

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