|The Communications Specialists TP-38 Shared Repeater Tone Panel is an earlier (and now discontinued), less sophisticated version of their current TP-3200 repeater controller. It was built for the commercial two-way radio market but can easily be adapted for Amateur repeater use. The TP-38 provides all the interface functions needed to control and to operate an Amateur VHF/UHF voice repeater. I am using one in an upgrade/replacement 70 cm. voice repeater now under development, and it is working very well.|
[For background, from the 1960s onward in the U.S. commercial land mobile radio service (typically on the 450 - 470 MHz band) multiple customer groups were licensed for and cooperatively used common ("community") repeaters. Every customer group using an individual repeater was assigned a different tone from a group of thirty-eight standard sub-audible CTCSS ("PL") tone codes for their user transmitters, and the steering of a particular repeated transmission into the intended group of user receivers was done on the basis of the repeater's retransmitted tone frequency. Unless their mikes were taken off-hook, the users heard only those repeated transmissions intended for their specific group. The TP-38 facilitated this style of community repeater operation.]
The TP-38 operates from an external 12 volt d.c. source, is microprocessor-controlled, and occupies just one rack unit (1.75 inches) of height in a conventional 19 inch relay rack. Operation of the TP-38 is completely independent of the frequency band used by the repeater. Excellent documentation was produced for the TP-38 and is still available on the Communications Specialists Web site.
The TP-38 allows the repeater operator to program which one(s) of the thirty-eight tones will authorize and enable operation of the repeater transmitter. Any number of tones, up to all thirty-eight, may be used. The chosen tones are programmed into and out of the TP-38's non-volatile memory registers from a front panel keypad and LED display (an access code/password is required for all programming). There is no RS-232 interface port, but almost all of the programming and data retrieval work can also be done remotely by radio if an auxiliary DTMF board has been installed.
When operating, the tone panel filters and decodes tones included in the repeater receiver's raw discriminator output, validates them against its programmed tone list, regenerates the tones for sending to the transmitter, couples (filtered) repeat audio from receiver to transmitter, and provides the push-to-talk signals to operate the transmitter. However PTT is derived only from the TP-38's detection of register-programmed PL tones; this is not a "carrier squelch"-operated controller! PTT will not occur if an unauthorized tone is used. The TP-38 also includes user-adjustable electronic timers for carrier drop-out delay and repeater time-out functions, and analog adjustment pots for transmit audio and PL tone levels.
Twenty-four programming commands and five PC board jumper options provide a considerable amount of operating flexibility. The PC board layout is open and easy to work on. The radio hardware I/O signals are brought to an eight pin barrier strip on the rear of the case and the required I/O voltages are specified. Interface wiring plans for some commercial radios (typically the classic Motorolas, General Electrics, RCAs, and Johnsons) are available.
Additionally, the panel will collect and report (upon operator command) the repeater usage statistics (total number of accesses and total elapsed usage time) for each authorized tone.
The "community repeater" style of operation is disappearing as former commercial customers have moved on to more advanced private and public trunked radio systems. The old repeaters are coming out of service and these TP-38 panels will be showing up on the surplus equipment market. They will make excellent low-cost, high-reliability Amateur repeater controllers for repeater operators who are willing to seek them out and to work with them. Similar comments apply to the TP-3200, still currently available from the manufacturer at an attractive price.