# Use of inductor in a receiver

1. Mar 10, 2014

### neeraj kaira

What is the use of inductor in a receiver? It amplifies the signal or it only blocks the high frequency signals?

2. Mar 10, 2014

### PhysicoRaj

The inductor in a reciever is the part of a tank circuit, you may call it a tuning circuit which selects the frequency ( your station).

3. Mar 10, 2014

### neeraj kaira

To tune the frequency i think there is a variable capacitor which selects the transmitted frequency.

4. Mar 10, 2014

### PhysicoRaj

The variable capacitor along with the inductor acts as the tank ckt. See This.

5. Mar 10, 2014

### meBigGuy

Radio receivers essentially use an RC tank circuit that resonates at the desired frequency. The variable capacitor certainly adjusts frequency, but it cannot do that without an inductor. Generally, the frequency at which the inductive reactance equals the capacitive reactance is called the resonant frequency.

http://en.wikipedia.org/wiki/LC_circuit

6. Mar 10, 2014

### neeraj kaira

Yeah i got this thanks.
I have a transmitter which sends the signals 90-120 mhz due to a variable capacitor 0-100 pf but the range of this arrangement is only 10-15 metres :( i want to increase the range what should i do?

7. Mar 10, 2014

### PhysicoRaj

8. Mar 10, 2014

### neeraj kaira

This is the circuit.

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9. Mar 10, 2014

### PhysicoRaj

Not concerning the details of the circuit, I hope this will do: Increase the input voltage. Add an amplifier (you will find details on these at the flick of a search in google). Increase your antenna length, or try to direct the signals in a particular direction you want. And this one :http://www.zen22142.zen.co.uk/Analysis/efftxd.htm

10. Mar 10, 2014

### neeraj kaira

Thanks :)

11. Mar 10, 2014

### Staff: Mentor

Keep in mind your country's regulations about "private" radio transmissions. There is likely a limit on the effective power that you can radiate before potentially getting into trouble with the authorities. Or with your neighbo(u)rs.

12. Mar 10, 2014

### anhnha

I always wonder why the LC tank resonates at the resonant frequency not other frequencies.
It would be great if you could explain it.

13. Mar 10, 2014

### Jony130

Because only for this one frequency Xc = XL and for the parallel tank circuit equivalent impudence reach his maximum value. So only for this frequency no current is drawn from the source. And this means that the current is circulating between the inductor and the capacitor, so we have a resonance circuit.

14. Mar 10, 2014

### sophiecentaur

An arm waving explanation about how a tank circuit works: If you charge a capacitor, it holds energy. When you connect an L across it, current will start to flow through the L, discharging the C. The current in the L produces a magnetic field, which stores energy. When the C has discharged, all the energy is now in the L. Current continues flowing in the L, charging the C in the other polarity, until the current is zero and the C is fully charged again - in the opposite sense. The process continues, with current sloshing around and the energy going back and forth at a frequency determined by the L and C values. This is the natural frequency of the circuit. If you apply a small signal at this frequency to an LC circuit, the supplied energy will build up in the circuit because each cycle of the applied signal is in step with the cycles of the energy sloshing back and forth. The amplitude will build up - in the same way that a pendulum / swing will build up its oscillations if you push it at the right rate. This only happens for applied signals with around the right frequency. Signals off frequency get out of step and there is no build up. This means the resonant circuit will 'select' only signals around the resonant frequency and reject others.

Making a resonant circuit is relatively easy at lowish Radio Frequencies as you can calculate the values of L and C. At frequencies around 100MHz, the components may not do exactly what's been calculated and there is a certain amount of 'green fingers' and experience needed to make a good resonator and an amplifier that actually works. You should look at Google Images of 100MHz amplifier circuits and see if there are any that you think you could build. (they can be very complicated)
This is an example of a circuit design for a 1W transmitter.

Unfortunately, an RF amplifier is not the easiest thing to start a career of circuit building with. Perhaps an off the shelf transmitter would be better - but not cheap, of course.

15. Mar 11, 2014

### meBigGuy

The capacitive reactance is opposite sign of the inductive reactance, and they are equal at the resonant frequency, so they sort of cancel (in a series resonant circuit). But only at the resonant frequency. The remaining resistance (which cannot cancel) determines the quality of the circuit, which is called the Q. The higher the Q the narrower the tuning bandwidth.

http://www.electronics-tutorials.ws/accircuits/series-resonance.html
http://www.electronics-tutorials.ws/accircuits/parallel-resonance.html

Regarding your transmitter.... How do you know the fault is not with the receiver? Or the antennas? Are you using properly designed antennas and connecting them with properly matched transmission lines?

16. Mar 13, 2014

### neeraj kaira

Receiver is my cell phone so i think it can't be the problem ..

17. Mar 13, 2014

### sophiecentaur

What frequency do you think your phone is using? How do you think it can receive the signals you are producing?

18. Mar 13, 2014

### neeraj kaira

19. Mar 13, 2014

### neeraj kaira

I transmit the signal using a mic and receive via my cell phone ...but range only 10 metres :(

20. Mar 13, 2014

### sophiecentaur

Are there any Analogue cell phones around, these days?

And, if you look at this link you will see the operating frequencies.