Use of VFO in transmitters

[demetal]

Hi,

What is the main purpose of using Variable frequency Oscillator in transmitters and receivers.... What is the dependency of its frequency to the system...?


Thank you

 

[betwixt]

The VFO is normally the part you adjust to set the frequency you transmit or receive on. It's the "tuning control".

Brian.

 

[demetal]

Can you please elaborate it ... Is VFO and Local Oscillator same....?

 

[betwixt]

Usually yes although it is possible in some systems that there is more than one local oscillator. In most cases VFO = variable frequency local oscillator, one you adjust to set the frequency rather than being fixed frequency.

Brian.

 

[demetal]

So which is the best method for generating Variable frequency... analog type or Digital type like DDS .....

 

[betwixt]

As far as RF goes, it doesn't really matter. Each type has it's good points and bad points, analog can give better noise performance but it more prone to mechanical effects such as vibration and expansion/contraction as temeperature changes, these cause drifting of the frequency. DDS is more stable because it is referenced to a quartz crystal timing source but being digitally controlled it needs additional computing power to set the frequency.

Brian.