This is the Motorola outdoor cabinet that the receive site is mounted in. This photo was taken when it was located in the office at the Range Township Firehouse in Sedalia (Midway) Ohio.
Here are two views inside of the cabinet - front and rear. The GE transmitter is at the top, the Motorola receiver and controller card in the middle, and the monster power supply on the bottom.
This is a close-up of the GE Mastr-II transmitter mounted onto a 19" rack panel. Below that it the Motorola Spectra-TAC chassis that holds the Micor receiver, audio-squelch board, and controller card.
This is the new microprocessor-controlled controller card that is installed in the Spectra-TAC chassis. It was under development for 6 months. The goal was high performance, low cost and simplicity. There is only one adjustment to calibrate. It contains a DTMF decoder, CTCSS decoder, and a PIC microcontroller to run the whole show. The complete schematic and layout is here. (PDF -1MB). The controller has several modes, such as carrier access, CTCSS access only, carrier access with CTCSS boost, and others. During periods of interference, it is possible to put the site into CTCSS protect or disable it completely for 1 hour, then it will automatically return to its previous mode.
The CTCSS decoder is also a PIC microcontroller, using a specialized version of a FFT (Fast Fourier Transform) called the Goertzel Algorithm to detect the CTCSS tone.
This is the antenna configuration at Mt Sterling. The tower is about 70 feet high, and our antennas are side mounted at about 55 feet. The 2 meter receive antenna is a Hustler G6-144B, and the UHF link antenna is a PC-Tel BMOY-4450.
The Tri-County Firehouse #491 in Mt. Sterling, OH, located on SR-56 at US-62 in the center of town. The tower is directly behind the firehouse, as seen here in the middle of the photo.