New FMTV Modulator

Modulator PCB

Sound PCB

Display PCB

Interface PCB


New FMTV Modulator

Design features:

Made for the PAL colour system
Can be used on more than one band
Adjustable sound sub-carriers frequencies and can be switchable
Frequency agile oscillator- i.e. 1100 MHz to 1400 MHz at the IF.
Uses protocol converter technology
Common serial bus between boards
Software upgradeable
Made for ATV applications

Circuit Description:-

The circuit is based around the Motorola Microcontrollers (MC68HC908 QTI & QY4). The software has been put together by Keith ZL1BQE and the hardware was created by myself Grant ZL1WTT. Most of the television modulator functions are settable from the display board, which talks down a serial communications bus to all of the other boards. Each of the other boards has a protocol converter located on it. The protocol converter has a four byte ASCII name for identification, for example, the soundboard responds to 'KAS1'.

The K is the software designer ident i.e. Keith. The A is for amateur television for this project. And the S1 is for soundboard number 1. This indent works the same way for all of the boards as in the block diagram above. You can also add more then one sound / modulator board for use on more then one band.

Software

The software functions that control the transmitter and the readout can be set to display the IF (23 cm band) or be set with an offset for higher bands. This would be the TX offset of +9.1 GHz L.O. for the 3 cm band. The correct RF frequency would then be seen on the display. Sound sub-carriers A & B offsets are displayed on the second row of the LCD display. Sound sub-carriers A & B are displayed, by changing from A / B to a X will result in that corresponding sub-carrier being turned off. The modulation can be changed from positive or negative going modulation, showing + or - at the end of the top row of the LCD display, and it controls a relay on the modulator board. Video inputs A & B are switchable from internal to external. Video gain is adjustable in steps from 0 to 99 which will let you set your level of deviation.

ATV Modulator user manual

All the information above can be stored in the EEPROM with a 16-character name.

Text / Drawings Copyright (C) 2003 ZL1WTT