# Type of Oscillator used in FM stations

#### sagarin

Joined Mar 27, 2007
6
Greetings to all.......

As you know there are many types of oscillators like crystal oscillators, R-C, R-L, which dont produce a freuency in the FM range(88-108MHz), What is the kind of oscillator used in FM stations? Can you explain?

#### Dave_

Joined Mar 22, 2007
28
In the Armstrong FM System for example, the crystal oscillator, at for example 10.8MHz, is mixed with the carrier frequency (12.8MHz). The difference in frequencys (2MHz) is then fed into a frequency multiplier (x48)
Which is how you get the higher frequency range.

#### Dave_

Joined Mar 22, 2007
28
We would generally use combinations of x2 and x3 to boost the signal up to its required frequency.

Here's some blab about the frequency multiplier from my course notes:

A frequency multiplier is a combination of a nonlinear element and a bandpass filter. A transistor operating in class c mode (less than 50% conduction) and a tuned LC circuit to an nth harmonic of the input modulated signal are commonly used for multiplication factors n from 2 to 5. In principle, we may tune the LC circuit to any integer number of the fundamental frequency, but efficiency drops off significantly for n>3. Where higher orders of multiplication are required, multipliers may be cascaded.

#### antseezee

Joined Sep 16, 2006
45
Greetings to all.......

As you know there are many types of oscillators like crystal oscillators, R-C, R-L, which dont produce a freuency in the FM range(88-108MHz), What is the kind of oscillator used in FM stations? Can you explain?
Typically a crystal oscillator is used, in conjunction with Mixers & Frequency Multipliers to get the same effect. 2's & 3's are stacked to get the multiplied frequency. For example, if you want a higher FM radio station, you need a VERY high oscillator amount which can be a smaller value crystal, sent through multipliers (a 3, 3, 3, 3 = 81). Then, you would need a slightly smaller mixer tuned to a portion of the Oscillator's frequency, since the difference of the Oscillator & Mixer is the resulting frequency that gets aired.

Armstrong is a great example of a FM transmission system. It's better if you saw a block diagram showing the process. Sometimes they throw in 90 degree phase shifters depending upon the system.