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Voltage controlled oscillator- help

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whiz115

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Hi i have some questions about the stages and anything else required for a descent FM transmition... as far as i know we need a VCO and a linear (amplifier)...i understand that the VCO produces a stable frequency so we can broadcast without frequency rolling...

1) Are there any other stages needed for broadcasting?
2) where do i apply my audio signal?
3) What is bridge?

also i would like if someone has time to explain with simple words...the way a VCO functions...

thank you.
 
1) An audio amplifier is normally required with pre-emphasis. A buffer amplifier on the output of the voltage controlled oscillator is also a good idea to prevent the frequency from drifting too much.

2) To the input of the VCO, obviously.

3) A means to cross a road, river or train line? It depends on the context, an h-bridge, a bridge rectifier, a bridged output on a aduio amplifier? This question is meaningless on its own.

Here's a VCO and output buffer with the waveform is shown below. Note that this circuit lacks a preamplifier or pre-emphasis.
 
The audio is generally applied to the varactor diode and causes the FM modulation. The responce of the loop filter has to be wide enough to allow the audio to shift the frequency of the VCO.
 
what is pre-emphasis?

this link shows some devices which i referred before when i said bridge..
**broken link removed**

it is supposed to measure a returning signal from the antenna but i don't
know what what that means.
 
FM stations equalize the audio with pre-emphasis which is treble boost. Then FM radios have de-emphasis which is treble cut so the audio is back to normal but any hiss is also cut.
Cheap toy FM transmitters don't have pre-emphasis so they sound very muffled when heard on an FM radio.

The amount of pre-emphasis and de-emphasis is less in Europe because they developed FM radio after it was in North America.

A SWR (standing-wave ratio) meter measures fairly high power transmitters. It uses a bridge circuit to measure how much signal is reflected from an impedance mis-match at the antenna. The reflected signal is power that is wasted because it is not transmitted. If the impedance match is very bad (disconnected or broken antenna) then the output transistor could be destroyed.
 
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