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1 Watt PLL FM Transmitter Circuit by Veronica Kits

This 1 Watt Crystal-Controlled FM PLL Transmitter was designed by Veronica Kits in the UK. It features very stable frequency output (Phase Locked Loop) with approximately 1 Watt power.

Screenshot: 1 Watt PLL FM Transmitter Circuit by Veronica Kits

I've built this transmitter kit MANY times in my career (used to get them from Stephen Moss at NRG Kits, which is also in the UK), and apart from one or two small problems, I can definitely attest to the fact that it is a fantastic PLL FM transmitter or exciter.

The circuit is comprised of a varicap VFO, which is controlled by the PLL section, which keeps the output frequency extremely stable. There are a total of 7 integrated circuits (8 if you want to include the 7805 voltage regulator), along with lots of resistors and capacitors, inductors, etc.. Overall, the circuit is very easy to build, but you will need to make some effort to get the right PCB built (or buy it - this page provides a link to buy one).

There are 2 LED's which indicate whether or not the transmitter's crystal-controlled PLL section is in or out of a locked state. Unfortunately, one of the problems with this FM transmitter is that it can jump out-of-lock if it is given a very heavy low-bass frequency, since it's only single-speed PLL. Dual-speed PLLs generally do not suffer from this low-bass problem, which occurs when the bass interferes with the PLL feedback filter, I believe.

Another slight annoyance is that the VFO and power amplifier sections require tuning (alignment) whenever there is a change in operating frequency. This means that you will do yourself good by having an RF power meter in your toolbox. Even without a power meter, tuning the transmitter is pretty easy because the two lock LEDs tell you when the VFO section is tuning, and there is an output-power LED that gives you a bit of a helping hand in tuning for max power. the brighter the LED, the more RF power. It doesn't indicate SWR though.

Frequency tuning of this transmitter is done through DIL/DIP (Dual-In-Line) switches. A frequency switching table is provided - so you can easily adjust the FM transmitter to your frequency of choice.

  • Freq. range : 100KHz steps from 87.5 to 108Mhz
  • Freq generation : Crystal Ref. Phase Locked Loop
  • Freq. stability : +- 1KHz max. Typ. +- 500Hz
  • Lock Time : 3 sec.
  • Spurious emission : Better than -45dB rel. to carrier
  • RF Power Output : 900 mW min. (50 ohm)
  • RF Output connector : SO239
  • Power supply : 13.8v DC regulated
  • Audio input sensitivity : 0.775V rms for 75Khz dev.
  • Signal to noise ratio : 75dB
  • Audio freq. response : flat from 20Hz to 76KHz
  • Pre-emphasis : none or 50us
  • Audio distortion : better than 0.2% THD
  • Audio input connector : Phono socket
Alternate References:
harriet06 says: (January 16 2008, 4:37am)

this is so great.it can help us a lot in our research problem about electronics.

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