Digital Synthesis FM Transmitter

This FM transmitter project was started back in 1991 and completed sometime around 1993, long before IT Group was legally registered as a company in Romania. The original business idea was to target the east-European FM radio stations market which at that time was totally untapped, but the project eventually succumbed to the perennially corrupt Romanian bureaucracy (and, sure enough, Marconi, Philips and the likes happily seized the opportunity and hit the jackpot all over eastern Europe). Interestingly enough though, FM technology didn't really change at all since the early nineties (except only for the disappearance of the eastern-block OIRT standard), so the modules developed for this project remain technologically valid to this day.

Digital synthesis exciter, programmable frequency, dual band OIRT/CCIR

• programmable frequency (decimal rotary switches, or up/down/set buttons with 7SD)
• wide band PLL
• 10 KHz increment
• direct synthesis (no frequency multipliers from FM oscillator to output)
  
• dual band
• OIRT: 66.00 - 73.99 MHz
• CCIR: 88.00 - 107.99 MHz
• stereo encoder
• PWM optical coupling between audio and RF modules (ground noise proofing)
  
• RF output: 1 Watt / 50 Ohm
  

Wide band tank, CCIR band

• wide band RF amplifier
• CCIR: 88.00 - 108.00 MHz
  
• RF input: 1 Watt / 50 Ohm
  
• RF output: 100 Watt / 50 Ohm
  
• VSWR and thermal protection
  

Digital synthesis exciter, factory-preset frequency, OIRT band (obsolete)

• factory-preset frequency
• narrow band PLL
• narrow band analog RF multipliers (two stages, x3 each stage, x9 total)
  
• analog tuning of the RF stages
• OIRT band: 66.00 - 74.00 MHz
• mono, but accepts stereo MPX
  
• RF output: 1 Watt / 50 Ohm