Q&A for How to Create a Simple AM Radio

The 741 is common (LM741, MC1741, etc.). Whatever you use, download the datasheet for it to see which of the pins has power, ground, + and - inputs and output. Some op-amps are dual (2 sections, like the 1458) so only one section will be used.

Yes, there is a way. You will have to solder all the components together. It's not a good idea for newbies, though: the breadboard is a better option.

You can use more windings in your inductor, or get a variable capacitor with a larger range for more channels. (Most of the time the problem can be solved with more windings.)

You can use images on the internet as long as you're able to read the circuit parts.

You should use the middle pin and either one of the side pins. The middle pin is connected to the shaft that decides the capacitance, so you can use the middle one in combination of either of the other two.

Yes, but it would lower the coil's self resonant frequency, though probably insignificantly. Meaning, the radio will tune to a slightly different frequency, yet without losing signal strength..

Yes, it would work. The capacity of "223p duplex radio Variable Capacitor" is listed as: 60 pf / 140 pf. Adding the two sections of the capacitor together gives 200 pf. It seems the "223p" is signifies a part number, and it is not the capacitance in pF. The model "223p" has 3 pins, and "224p" has 4 pins.

Yes, it will do. A smaller capacitor will simply limit the frequencies that the radio can tune, so you will miss the stations at the lower frequencies. You can compensate in two ways: 1) by making your coil longer and 2) by adding a small capacitor or even a second 120pF variable capacitor in parallel with the first one.

The range depends on the power of the transmitting station and the sensitivity of the radio. It is in the order of a 20-30 km if there are no obstacles, e.g. buildings, hills. The longer the antenna, the more electromagnetic waves can be collected, so stations can be further away.

Solid wires are easier to push through the holes in the breadboard, but are not as flexible. Multi-strand wires will splay when inserted in the breadboard, which can cause short circuits, unless the ends are tinned, then they behave just like solid wires.

A telescopic antenna is not very suitable for a simple radio, it does not collect enough electromagnetic waves. If you are very close to the transmitting station, then a very short antenna like a telescopic antenna will do.

This circuit will not work at 5 volts because of the operational amplifier needs a minimum of ±4.5V - i.e. a 9V battery just barely satisfies this requirement. A different circuit would be needed.

No, it doesn't need to be stripped at the far end. Electromagnetic waves can penetrate the insulation because it is so thin.

Electronic components were found by different people experimenting with electricity and observing electrical phenomena. For example, resistance in wire for resistors, capacitors are related to static electricity, inductors are related to electromagnets. Semiconductors diodes were discovered while investigating the electrical properties of copper oxides and sulphides, the vacuum tube or valve was invented in 1904 and until the transistor was invented at Bell labs in 1947, radios and TVs were made with vacuum tubes. Progress is also made in physics, chemistry, and engineering and the knowledge helps to make new and better devices. Each component history is different and could fill a book.

Yes, you can. The circuit works better with higher impedance speakers, from 75-100 ohms (you may see ohms as the symbol Ω), so choose a headphone around 32 - 64 ohms or more. There are headphones with 250 ohms or 600 ohms available but they tend to cost more. Ordinary headphones with impedance of 8 ohms will give very low volume, only very strong stations will be heard, if at all.

A high impedance speaker of 75 to 100 ohms would work better in this setup. Low impedance speakers of 8 ohms will result in lower sound and make some stations inaudible. An earpiece (earphone) for a mobile phone is usually 32 ohms and will give results in between the previous two speakers.

With the inductor of ~370 μH and the variable capacitor at 200 pF, the lowest frequency is about 585,000 hertz (Hz) or 585 kilohertz (kHz). With the capacitor at the lowest value, say 10 pF, the frequency is about 2.616 megahertz (MHz). The actual frequency may differ quite a lot from this because the wires, the breadboard, etc. also have capacitance which adds to the total capacitance. For example, with 20 pF, the calculated frequency is 1.850 MHz. Using a 20 μH inductor, the frequency range is 2.5 MHz to 8 MHz.

The inductor in this project is about 370 μH and together with the 200pF variable capacitor, it is suitable for the AM Medium Wave broadcast band. The inductor in the video "DIY Radio in less than 5 minutes!" is about 20 μH and works in the AM Short Wave band.

The inductor and variable capacitor make what is called a tuned circuit, which has two functions: to separate radio stations and when it is tuned, to increase the voltage available from the antenna. If you do not put in the inductor, the antenna wire itself has a tiny inductance, so you will need a very long wire to get any signal, and the stations will be mixed together; it won't make a good radio.

Yes, you can. The total capacitance or value of the capacitors increases when they are connected in parallel, e.g. two 10uF capacitors will equal 20uF. The value is actually not very critical, you can use 5uF to 50uF and it will work. Conversely, the total capacitance decreases when placed in series, it is found by adding the reciprocals of the individual capacitances, and taking the reciprocal of the sum, according this formula 1/(1/c1 + 1/c2 + 1/c3 ...).

You can make your own simple AM radio antenna using a piece of wire. Use a small diameter insulated wire, such as a 20 or 22-gauge, and cut it to a length of at least 15 or 20 feet (4.6 or 6.1 m). To boost the reception, coil the wire in a circle and use zip ties or electrical tape to keep the coil from unraveling.

AM and FM are different types of radio waves, each with their own advantages and disadvantages. AM radio waves have a shorter bandwidth and are more susceptible to interference, which is why AM radio has a poorer sound quality. But, the longer radio waves of AM mean they can be transmitted and received over greater distances and through barriers. FM radio has better sound quality but can't travel as far and is impacted by physical barriers.

On a basic level, a radio works by deciphering radio waves and turning them into sound. To do this, a radio uses an antenna to pick up the radio waves that are broadcast in the air all around us, which causes electrons inside of it to vibrate. The way these electrons vibrate is then translated into sounds that come out of your speaker.

The variable capacitor is usually attached to the tuning knob, labelled 530 to 1600 kHz (AM), or 88 to 108 Mhz (FM) or both at the same time. For other radio bands, such as LW or SW, the numbers are different. On a radio with a linear dial, the tuning knob pulls a string to turn the variable capacitor, the string carries a pointer to indicate the frequency. If the tuning is done using a potentiometer, or using up and down buttons, the radio does not use a variable capacitor for tuning, but uses a varactor diode or a computer chip.

The range is 10-20pF in the low end and 200pF in the high end. Other variable capacitors of higher values can be used too, the number of turns in the coil need to be reduced to maintain proper range.

The antenna picks up electromagnetic energy and creates a tiny current which is sent via the 33 pF capacitor to the resonant circuit (the inductor and variable capacitor). Much like pushing a pendulum or a swing, if the frequency incoming signal is the same as the frequency of the resonant circuit, the amplitude (voltage) increases across the circuit. We say we have tuned the signal. Next, the signal is both demodulated and amplified by the op-amp and sent to the speaker.