How can a capacitor be used to capture rf signals?

Hello Sir,
I would like to understand how a capacitor is used to capture the rf signals.

where did you get that notion?

maybe what he meant is the varicap used in am/fm radio

This question is too vague to answer correctly but I think you may be talking about a sample and hold circuit wherein a capacitor is used to momentarily store an instant in time of a signal, perhaps to be read by an A-D converter. However ac capacitor cannot "capture an RF signal" per se.

What is RF ?
What is a Capacitor ?

What is the function of a Capacitor ?

What is a Tuned Circuit ?
What is Tank Circuit ?

What is an Inductor ?

Explain how you would utilise an Inductor and Capacitor in an RF Circuit ?

Provide a simple circuit for the detection of RF frequencies ?

Im not saying anymore to this except read through my questions and go and do some research

You can not capture RF but you can capture the data that are modulated on it and you can capture the power of the received RF signal and store it in a capacitor after detecting (rectifying) it. You can even charge a battery with that rectified RF signal.provided that the received signal is strong.

Hi Mark, look like nobody could answer you, let me try.
1. RF = Radio Frequency

2. A Capacitor is two metal plates close to each other, separated by air or other non conductive material.

3. Not possible to state all functions here: smoothing, timing, DC insulating, tuned circuits etc.

4. A Tuned circuit is normally a Inductor and capacitor in parallel.

5. A tank circuit is a tuned circuit in a metal box.

6. An inductor is a coil made of conductive wire, normally copper wire it can also be a printed line on a PC Board in ultra high frequencies it can be in the form of a metal tube.

7. As a tuned circuit, as oscillator, filter etc.

8. Diagram

The capacitor can be used to capture rf signal, only if its incorporate a coil across the capacitor to form a tuned circuit. Make the tuned circuit in resonance to capture desired rf frequency signal.

I am pretty sure there is no use of inductor in the circuit, rather it has something to do with the leads of the disc capacitor. I coudn't find anything on it yet. But thanks for helping.

Suyash RF is an alternating signal at high frequency and there is no way to capture it and by capture I'm talking about recording it. Who ever told you that it is possible to capture RF don't know what he is talking about, Remember a capacitor consist of two metal plates connected to two leads, one plate charge positive and the other negative and if you apply an alternating current to it, it will charge and discharge on one plate positive when the signal go positive and it will discharge as soon as the signal go negative and will charge negative on the negative sickle. See the diagram that I posted, after the diode you connect another capacitor of a much higher value than the one in the tuned circuit and this one will then eventually charge up to the RMS value of the received RF signal.

On the other hand, if you connect the two leads of a capacitor together it will form a tuned circuit and it will resonate at a very high frequency depending on the value of the cap. and the shape of the leads, if it is a say 12pF then it will resonate at about 400MHz.

Well, see... the term "capture" needs to be elucidated.

"Capture" as in:

* received and demodulated?
* collect the energy of, so it can be applied to the powering of something else?
* in a resonate cavity, or some sort of containment field, ala capturing a photon?
* as if it were a living thing that you want to display in some other-worldly zoo along with captured lightening bolts, and captured cosmic rays, to be exhibited on the Dark Side of the Moon [not necessarily the Earth's moon]??!?

Steve I don't think Suyash is so advanced that he can understand your statements, in any case it is not necessary for the RF to be modulated to capture the DC component of the received RF signal, as a matter of fact, an unmodulated RF will give you a more stable DC after it's rectified than a modulated RF. I once designed and build a receiver that was powered by the RF it received and here I'm not talking about a crystal receiver but a super regenerative receiver with amplifier stages.

But, aren't you making assumptions about what Suyash means when he says "capture"?

And, COOL, regarding at super-het receiver powered by the signal! That's amazing. I'm assuming headphones, right? Or did you manage to acquire enough energy to drive a speaker?

I really don't think it is necessary for me to answer that sarcastic question and read again there is a difference between a super-het and a regen, Oh sorry that was before your time in the days of the cathodes grids and anodes and what I meant are, you are talking in riddles that very few people can understand "dark side of A moon" is it full moon yet?

Sorry, I didn't mean for it to sound sarcastic -- I am truly impressed :)

And, sadly, I DO go back to the days of grids and filament heated cathodes--just barely
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[Once a month, roughly, {or is that once a 'moon'} the dark side of the moon directly faces earth. But this can only be seen by the bare eyes of us 'animals' during a total solar eclipse--at least that's true on this planet--to me that is eerily poetic]