Description

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.
A 4dB attenuator allows the VCO to drive the MSA1105 RF power stage without exceeding the 1dB gain compression.

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.
_+17dBm output power level (50mW).

Conclusion:

This new FM transmitter is definitely more simple to assemble but more expensive than the previous versions.

 

VCO/PLL Schematic PDF File