Michel P Website
FM Synthesizer N°2


synthèse rapide du RDS

This new FM transmitter is very easy to make and doesn't need any RF tuning.

First of all ,we have used an integrated VCO: The POS150 from Mini-circuits.
This excellent RF circuit covers all the FM Band in a voltage range of 4V to 8V.
The Kvco factor is very stable all over the FM band, consequently, we have applied the AF signal directly on the control voltage line coming from the PLL.
The VCO drives directly a new RF stage amplifier in order to get 23dBm at the output.
To reach this target, we have used a BFG135 transistor with few components to adapt the input and output impedances to 50 ohms.
All the components have been determined by using Genesys software tool.

Finally,a low pass filter ensures a good harmonics rejection.(H3<-60dBc).

This new design conducts to new RF performances like:

_Phase/noise equals to -103dBc/Hz at 10KHz from the carrier.
_+23dBm output power level (200mW).




Power Output
Frequency Output
87.5MHz to 108 MHz
Frequency Step
Phase Noise
Frequency Stability
+/- 200Hz
Harmonic Filtering (Except H2)
Spurious Emissions
Direct Frequency Modulation
MPX Input Response
+/-0.5dB 40Hz to 80KHz
MPX Input Level
450mV RMS Min
Power Supply
14 to18V
Consumption current



This new FM transmitter is definitely simple to assemble but more expensive than the old version.


Présentation détaillée RDSVCO/PLL Schematic PDF File

Measurements (PDF File)

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