Display board
Display board
The display layout shows the transmit frequency (T) on the top line. At the end of the top row there is a +/- symbol which indicates the type of modulation, and the bottom line displays both sound sub carriers frequencies. The A and B indicate not just sound channel A or B, but by changing the letter to display a X, will turn off the selected sound channel. If the display starts to flash and starts showing the letter L, then the PLL is out of lock. The letter L will replace the T, A, B on the display to show which device is out of lock.
The display is based on the Motorola MC68HC908QY4 Microcontroller. The PCB is designed to fit in behind the front panel of a 1U-rack bin. On the front panel there are three push buttons, and a rotary encoder. The Display itself is a commonly sourced 2 x 16 LCD display, the EEPROM is a 24LC64 which is the location where the modulator settings are stored. The 10 MHz TTL referance oscillator is also mounted on this board. The serial communications, 10 MHz referance and common 13.8 volt supply are fed down a 10-way ribbon cable that is looped though all the printed circuit boards, with each alternative wire grounded to minimise signal radiation.
