change the frequency of the transmiter

Put on the oscillator pin ( say pin 11 ) a varicap and drive it witha DC voltage.

Mandi

Wrong information...

Pin11 serves as resonator input of Main Oscillator but synthesizer output is corralated by divider ratio and the reference oscillator frequency. Synthesizer frequency 32 or 64 times of the reference oscillator frequency so it's fixed by divison ratio and reference frequency.
To change the output frequency, the reference frequency that consists of a crystal oscillator ( or maybe similar external source ) should be changed and output frequency will be changed 32 times or 64 times of the reference depending on divison ratio..

BigBoss ( As name says ) is right. Just change the pin from 11 to 15 or 16 to change the frequency of the reference oscillator.
Just a Type mistake.

Mandi