Comments on: How does a RLC circuit work, and how do FM receivers use RLC circuits to tune into a radio station? http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station Mon, 30 Jan 2012 17:05:59 -0500 http://wordpress.org/?v=2.8.4 hourly 1 By: Roger http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station/comment-page-1#comment-334 Roger Tue, 02 Mar 2010 15:13:59 +0000 http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station#comment-334 The RCL circuit is tuned to resonate (XL = XC) at the frequency in question. Above resonance XL is greater than XC, while below XC is greater than XL. In a tank circuit the inductor and capacitor are connected in parallel, maximum signal is developed when XC = XL.The tank circuits in the front end is tuned to pass the desired station. Then the signal is converted to an if signal using an oscillator that also has a LC tank circuit to tune its frequency above the FM signal by 10.7 MHz. The oscillator and RF beat together in the mixer to make the IF signal.The IF signal is amplified by an IF amplifier tuned with tuned IF transformers circuits consisting of capacitors and coupled inductors. The FM detector uses a tuned transformer with capacitors. As the frequency in the detector's tank circuit changes the the current leads voltage at lower frequencies (below 10.7 MHz) and the detectors output will be negative. If the frequency is above 10.7 MHz, the detectors output will be positive. The voltage at the output is audio. This is basically how it is done.<br><b>References : </b><br> The RCL circuit is tuned to resonate (XL = XC) at the frequency in question. Above resonance XL is greater than XC, while below XC is greater than XL. In a tank circuit the inductor and capacitor are connected in parallel, maximum signal is developed when XC = XL.The tank circuits in the front end is tuned to pass the desired station. Then the signal is converted to an if signal using an oscillator that also has a LC tank circuit to tune its frequency above the FM signal by 10.7 MHz. The oscillator and RF beat together in the mixer to make the IF signal.The IF signal is amplified by an IF amplifier tuned with tuned IF transformers circuits consisting of capacitors and coupled inductors. The FM detector uses a tuned transformer with capacitors. As the frequency in the detector’s tank circuit changes the the current leads voltage at lower frequencies (below 10.7 MHz) and the detectors output will be negative. If the frequency is above 10.7 MHz, the detectors output will be positive. The voltage at the output is audio. This is basically how it is done.
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]]> By: billrussell42 http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station/comment-page-1#comment-333 billrussell42 Tue, 02 Mar 2010 14:38:59 +0000 http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station#comment-333 Forget the R, it's the LC part that is important. And it's not used to demodulate the signal, it's used to select and amplify the signal. Very simplisticly: An older FM radio has a variable capacitor and fixed inductor. The cap enables the user to adjust the C so that the parallel resonant frequency of the LC is at the frequency of the station you want to listen to. Actually there are two ganged variable caps, the first tunes the LC of the RF amplifier at the input the second adjusts the frequency of the local oscillator which beats against the amplified RF signal to form the IF frequency of 10.7 MHz, which is ampllifed further. If you don't understand parallel resonant circuit, this is meaningless, so read up on that first. .<br><b>References : </b><br> Forget the R, it’s the LC part that is important. And it’s not used to demodulate the signal, it’s used to select and amplify the signal.

Very simplisticly: An older FM radio has a variable capacitor and fixed inductor. The cap enables the user to adjust the C so that the parallel resonant frequency of the LC is at the frequency of the station you want to listen to. Actually there are two ganged variable caps, the first tunes the LC of the RF amplifier at the input the second adjusts the frequency of the local oscillator which beats against the amplified RF signal to form the IF frequency of 10.7 MHz, which is ampllifed further.

If you don’t understand parallel resonant circuit, this is meaningless, so read up on that first.

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]]> By: Chris K http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station/comment-page-1#comment-332 Chris K Tue, 02 Mar 2010 14:12:59 +0000 http://www.whksradio.com/fm-radio/how-does-a-rlc-circuit-work-and-how-do-fm-receivers-use-rlc-circuits-to-tune-into-a-radio-station#comment-332 Actually, FM receivers usually use phase-locked loops to demodulate the radio station. AM receivers use RLC circuits to demodulate the signal though... As far as how they work... it all depends on what specifically you want to know... Resistors drop voltage. Inductors resist changes in current and will make dramatic changes in voltage to keep it that way. Capacitors resist changes in voltage and will make dramatic changes in current to keep it that way.<br><b>References : </b><br> Actually, FM receivers usually use phase-locked loops to demodulate the radio station.

AM receivers use RLC circuits to demodulate the signal though…

As far as how they work… it all depends on what specifically you want to know…

Resistors drop voltage. Inductors resist changes in current and will make dramatic changes in voltage to keep it that way. Capacitors resist changes in voltage and will make dramatic changes in current to keep it that way.
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