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RF TUNING

Anum Ahmed Pirkani

Int roduct ion:

An RF tuner is a circuit module or standalone equipment that detects radio-

frequency (RF) signals of low amplitude and amplifies and converts them to a form

suitable for further processing.

In RF, the term tuning is

1) Adjusting the RF receiver to receive only the desired RF signal frequencyon

which, that particular circuit operates on

2) Then amplifies it to the level that signal processing is possible for the initiallyweak signal.

Since the antenna picks up thousands of radio signals at a time, a radio tuneris

necessaryto tune into a particular frequency (or frequency range). This is typically

done via a resonator (a circuit with a capacitorand an inductorform a tuned circuit).

Working:

The simplest RF tuner consists of an inductor and capacitor connected in parallel,

where the capacitor or inductor is made to be variable.

This creates a resonant circuit which responds to an alternating current at one

frequency. It is often followed by a diode which is used as a detector (detects and

allows the RF signal of a particular frequency to pass on to further stages of

receiver).

http://en.wikipedia.org/wiki/File:Tuned_circuit_animation_3.gif

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The capacitor stores energy in its electric field E and the inductor stores energy in

its magnetic field B.

An LC circuit can store electrical energy oscillating at its resonant frequency (the

desired frequency).

A capacitor stores energy in the electric field (E) between its plates, depending on

the voltage across it, and an inductor stores energy in its magnetic field (B),

depending on the current through it.

If a charged capacitor is connected across an inductor, charge will start to flow

through the inductor, building up a magnetic field around it and reducing the voltage

on the capacitor. Eventually all the charge on the capacitor will be gone and the

voltage across it will reach zero.

However, the current will continue, because inductors resist changes in current. The

energy to keep it flowing is extracted from the magnetic field, which will begin to

decline. The current will begin to charge the capacitor with a voltage of opposite

polarity to its original charge.

When the magnetic field is completely dissipated the current will stop and the charge

will again be stored in the capacitor, with the opposite polarity as before. Then the

cycle will begin again, with the current flowing in the opposite direction through the

inductor.

The charge flows back and forth between the plates of the capacitor, through the

inductor. The energy oscillates back and forth between the capacitor and the

inductor until no new signal is received.

The oscillation frequency is determined by the capacitance and inductance values.

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Where is RF Tuner used?

RF Tuner is used in high frequency RF circuits which operate at a narrow bandwidth

and receives a very weak signal which cannot be passed through signal processing

stages (demodulation/ decoding) until amplified to a certain extent.