Confusion About Simple AM Radio Receiver/Tuner

In summary: When the capacitor is fully charged, it blocks the current from the inductor so the oscillation of the inductor is stopped. This allows the radio to only receive signals at a specific frequency. The resistor R limits the amount of current that can flow through the capacitor. In summary, this circuit allows the radio to receive only specific frequencies. The circuit is made up of a transformer, a step-up voltage, a detector diode, a variable capacitor, and a resistor.
  • #1
Glenn900
4
0
I am confused by the design of this AM receiver/tuner circuit.

http://imgur.com/f9n05

I don't understand how the inductor and capacitors on the left design a circuit that resonates at a certain frequency, and I also don't understand why the resistor and capacitor in parallel after the diode create a low-pass filter.

Are the inductor and two capacitors not in parallel with each other? This circuit makes more sense to me if I consider the two capacitors to be in parallel with each other, and in series with the inductor. Then the inductor and capacitors should exhibit resonance at a given frequency and act as a band-pass filter, passing this specific frequency to the rest of the circuit. Is this right?

Can anyone help me out with this circuit?
 
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  • #2
In this circuit it doesn't matter if you consider the two capacitors in parallel are in series or in parallel with the inductor, the effect is the same.

Imagine the inductor as a mass that is being moved at a regular frequency by the antenna. The capacitors are like a spring that is alternately compressed and stretched by the oscillating mass. Since the spring keeps the mass oscillating, the antenna only has to supply enough input power to offset the losses due to friction. The oscillation of the mass will increase until the losses equal the power input from the antenna.

Likewise in the circuit, the voltage in the inductor-capacitor circuit increases until the losses equal the power supplied by the antenna. If the voltage is high enough, the positive peaks of the oscillation will pass through the diode and charge the capacitor. The 10K resistor allows the capacitor to discharge when the peak of the signal is less than the voltage the capacitor is charged to. In this way the voltage across the final capacitor follows the peak voltage of the signal. When amplified it provides an audio output.
 
  • #3
Glenn900 said:
I am confused by the design of this AM receiver/tuner circuit.

http://imgur.com/f9n05

I don't understand how the inductor and capacitors on the left design a circuit that resonates at a certain frequency, and I also don't understand why the resistor and capacitor in parallel after the diode create a low-pass filter.

Are the inductor and two capacitors not in parallel with each other? This circuit makes more sense to me if I consider the two capacitors to be in parallel with each other, and in series with the inductor. Then the inductor and capacitors should exhibit resonance at a given frequency and act as a band-pass filter, passing this specific frequency to the rest of the circuit. Is this right?

Can anyone help me out with this circuit?

There is a transformer at the left. This carries a signal from the antenna in the primary and the secondary is tuned with the capacitors so that it resonates with them at one frequency.

At this frequency, there is a step-up in voltage and this voltage appears across the secondary of the transformer.

This voltage is then rectified by the detector diode and the resulting waveform is filtered to remove the high frequency components, leaving only audio. This is amplified in the amplified speaker.

The capacitor C is variable and allows tuning of the parallel tuned circuit to receive different frequencies.
 

1. How does an AM radio receiver work?

An AM radio receiver works by receiving radio waves from the air through an antenna. These waves are then converted into electrical signals and amplified. The receiver then selects the specific frequency of the desired station and demodulates the signal to produce sound.

2. What causes confusion about simple AM radio receiver/tuner?

The main sources of confusion about AM radio receivers/tuners are the technical terminology used, the different components involved, and the process of tuning in a specific station. Additionally, the complexity of the technology may also contribute to confusion for those who are not familiar with it.

3. How can I improve the reception of my AM radio receiver?

To improve the reception of an AM radio receiver, you can try adjusting the antenna, moving the radio to a different location, or using a signal booster. Additionally, using a higher-quality antenna and keeping it away from sources of interference, such as electronics or metal objects, can also improve reception.

4. Can a simple AM radio receiver receive all AM radio stations?

No, a simple AM radio receiver may not be able to receive all AM radio stations. This is because different stations broadcast at different frequencies, and some receivers may not be able to tune into certain frequencies. Additionally, the strength of the signal and the distance between the receiver and the station can also affect reception.

5. Do I need any special skills to operate a simple AM radio receiver?

No, you do not need any special skills to operate a simple AM radio receiver. However, some basic knowledge of how the receiver works and how to tune in a specific station may be helpful. Most receivers also come with an instruction manual that can guide you through the process.

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