Hello my friends at Instructables, I hope you are having a good time meanwhile you are reading this, if it is not well... you need to put your hands to work in this AMAZING AM Radio Receiver Circuit, yeah! wanna get that almost free RF Radio waves from the air and to be listened by you ears?

Well... ¡it's showtime!

Definitely it is not a super regenerative or Heterodyne Receiver, not that kind of difficult stuff for many people who doesn't care about IF frecuency, AGC, RF filters, RF Cans, Decoupling Capacitors, Multiple Trimmers into a large capacitor and thing like that haha.

-And we don't use a all in one radio like the ZN414, MK484, TA7XXXX, one chip receivers in a TO-92 package, because in many places from the world is obsolete and hard to find :(

Plot twist:

-I tested this circuit and make some improvements on it. to listen many AM radio stations near and not very near from your home, and IT WORKS!!!

-You can control the RF GAIN, make son BIAS to the transistors to listen stronger and clear the Modulated Amplitude Radio Waves, of course this is not a simple Galena radio, but it has a better performance :)

Lets get started!

Step 1: MATERIALS LIST

For this project we will need:

3X 2N2222A TRANSISTORS OR ANY NPN BJT TO92 PIN COMPATIBLE like 2N3904

1X 5K Potentiometer

2x 1N4148 Fast Recovery Diodes

1x Female Headers (at least 25 pins)

1X 104 (100 Nano Farad Ceramic Capacitor)

1x 103 (100 Nano Farad Ceramic Capacitor)

1x Knob for the trimmer or you can use a plastic point metal screw driver

1x MONO/STEREO Female Audio Jack

1x AA Battery Slot

1x 3K9 Ohm 1/2W Carbon Film Resistor

1x 2K2 Ohm 1/2W Carbon Film Resistor

1x 1M Ohm 1/2W Carbon Film Resistor

1x 4K7 Ohm 1/2W Carbon Film Resistor

1x Female Headers (24 pin at least) for Connections & Soldering

2x AA Battery (Alcaline, Carbon, NiMH etc)

1x RF inductor (Hand Made) i explain how to make the inductor in the next steps from this instructable

1x Variable Capacitor (Trimmer) 1-55 pF

1x 5 pin of male headers (not showed) for easy plugging the audio jack to female headers.

Utilities:

-Soldering Iron

-Solder 60/40

-Flux

-Breadboard Wire (it's recommendable to use 3 wire colors at least)

-Third Hand Tool or similar.

-PATIENCE :)

Step 2: HOW TO DO THE RF INDUCTOR (AM COIL)

This is an IMPORTANT step cause this component is critical for the correct working at the desired frecuency range between (550-1500) KHz, the Modulated Amplitude Signal on earth.

Let's go, is MANDATORY to use a Ferrite Core from about 0.8 Internal diameter, it's not necessary to use a cylinder ferrite you can use a planar ferrite like me, if you don't wanna go crazy finding this core, you can recycle someone from an old FM/AM receiver.

Well, let's continue. The internal diameter is about 0.8 centimeters of internal diameter, and about 58-60 windings of enamelled cooper wire of 30 AWG. (take it easy winding the ferrite core and do your best, nothing it's perfect).

-You can use a little bit of glue, tape, or anything you want to maintain the windings in the place), see the images above to have an idea.

-Once finished the winding and applied glue to the coil, it's mandatory to scratch the leads fo the coil to remove the aislant from the wire, and try measuring continuity to make sure there it is and the coil is formed correctly.

Step 3: Circuit Diagram (Schematic)

The circuit diagram shown in this step it's the complete and tested circuit.

-The Soul of the circuit it's the tank circuit formed by (inductor and capacitor in parallel) to make the "catching" RF waves circuit determined by the formula: 1/sqrt((L*C), where L is the value in Henrys of the inductor, and C it's the total capacitance from the trimmer a.k.a (variable capacitor).

-The tank circuit it's calculated to work between 500-1500 KHz as said before.

-Once any frecuency between this range "catched" by LC will generate a voltage between the terminals of the tank circuit.

-that is feeded by 2K2 resistor and 100 nano farad ceramic capacitor (left in the schematic).

-the other terminal is connected to the base from the 2n2222 transistor connected in "cascade" or darlington mode to the second transistor to increase the current gain of the circuit.

-One collector from the first transistor goes to 1.6 volts the new vcc of the circuit and the collector from the second transistor goes is biased by a 5k precision potentiometer to make sure hear the weak stations and adjusting the hearing of the circuit, in other words it's biasing the transistor to make sure it works correctly).

-At the collector of the second transistor it's connected a 3K9 resistor (you can use a 2k8 to 3k9 resistor) testing try and error will make the best performance to your own circuit.

-as i saying the 3k9 resistor is biasing the tank circuit to make it stable and increase the gain.

-the 100 nano farad ceramic capacitor connected to the collector of the second transistor too is bypassing and avoiding the DC level and RF level, and only permits passing of most pure audio signals.

.the next circuit (right) is only a base biased amplifier formed by 1M ohms resistor connected between the collector and base of the third transistor and the 4k7 resistor connected in the collector and 1.6 v vcc from the circuit.

-The output signal goes to the transistor collectors and +3V vcc or the battery bay positive, to increase the power of the circuit, where is connected the high impedance earphones or an amplifier like lm386 etc.

Step 4: Soldering the Components

Due the simplicity of the project, you can use headers, female or male to make the connections, yes this was my idea from i got from an old electronics magazine (everyday practical electronics) and similars, but in this case with modern components and saving more space, the important is the functionality of the circuit.

Yeah whatever, we need at least 25 pins from the header, if you don't have all the necessary pins, you can use the bottom connections from the female header with more jumpers and so

-Solder the POSITIVE (Anode) from the 1n4148 diode to the first pin of the female headers.

-next solder the positive (Anode) from the second 1n4148 diode to the cathode of the first 1n4148 diode

-make sure the polarity it's ok, this will help us to have a voltage drop of about 0.7+0.7 volts or 1.4 volts from the 3 volts battery bay, and the circuit will work correctly with this voltage, you can use a single AA batterry and battery bay, but is very complicated to find a sold of single AA battery in many places, whatever. sure you can save costs quitting the 2 diodes and using a single AA battery instead, but the power, durability and stability from the circuit will be compromised :)

-The next step is to solder the cathode from the second diode to the second pin of the female headers.

-Now it's time to solder the 10 nano farad ceramic capacitor next to the positive jumper of 1.6 volts POSITIVE RAIL, it will be located in the 3rd and 4th pins from the female header.

-Is very recommended to use any type of protections of short circuit between the leads of every component with large terminals, in this case i used the cover from the breadboard wire.

-solder the 2K2 resistor next to the capacitor like in the pictures and the other lead goes to the positive rail according to the circuit diagram.

-The trimmer capacitor is located between one terminal of the 2k2 resistor and the 6th pin of the female headers.

Step 5: Soldering the Components

-Next to the trimmer we'll solder the first 2n2222 transistor, and the second 2n2222 transistor at the side.

-and the 5k trimmer goes into the action at the side of the second 2n2222 transistor and the third 2n2222 transistor at the end like in the pictures.

-be sure all are 2n2222 transistors or similar pinouts like, 2n3904, but ALL TRANSISTORS MUST BE NPN transistor, in other way the circuit won't work at all.

Step 6: Soldering the Components

-Time to make two bridges between the collector from the second 2n2222 transistor and the first pin the 5k precision potentiometer.

-The second bridge we need to make is between the 2nd and 3rd pin of the 5k potentiometer like in the pictures.

-Solder the 10 nano farad ceramic capacitor (103) between first jumper or bridge and the base of the 3rd transistor.

-is recommended to cover the capacitor leads with any kind of protective rubber like used wire covers.

-Solder the 1M ohm resistor between collector and emitter from the third 2n2222 transistor, keeping in mind to protect the lead of the resistor too.

Step 7: Connecting Positive and Negative Rails

-Cut exactly to the size the 4k7 resistor and protect the leads to match the connection between the second bridge of the 5k potentiometer and the last transistor collector.

-protect the leads of the 3k9 resistor (this value can vary between 1k8 to 3k9 ohms) you can prototype or use the most handy for your own circuit.

-Solder the 3k9 resistor to the collector of the second transistor and the 2k2 resistor lead or pin 5.

-----SOLDERING THE POSITIVE 1.6 VOLTS RAIL-----

-For an easy finding we'll use a red color wire, and first to connect in terminal to pin 2 or 1v6 positive rail.

-the other wire lead goes to second transistor collector, and the last connection goes to the second bridge of the 5k precision potentiometer, if you find hard to figure how the connections are making, you always can use the schematic showed in the first steps of this instructable.

Step 8: Connecting Positive and Negative Rails

-The 1.6 volts positive and negative rails must be checked twice or more times to ensure the correct connections from the schematic.

-Once you have connected the positive rail after the two 1n4148 diodes that drops the 3v voltaje from the 2x AA battery bay to about 1.6 volts, the negative rail goes from the third pin to the emitter from the second 2n2222 transistor. and then goes to the emitter to the last 2n2222 transistor.

ALMOST FORGET IT...

-Is needed to make a bridge with some wire between emitter and base from the first and second transistor to create the darlington or cascade connection between both.

-and to solder a bridge or jumper between the second lead or left lead from the trimmer that one that is not connected yet, to the base of the first 2n2222 transistor like in the pictures i show in this step.

Step 9: Soldering the RF Handmade Coil.

It's time to create the magic circuit that will tune the beautiful AM radio waves out there, almost for free :)

-Because we are making a tank circuit (in parallel) is mandatory to solder the coil in parallel with the trimmer capacitor, in other words, one lead to the coil to one lead of the variable capacitor.

-The coil was hand made but you can use and old or recycled AM/FM radio coil just in case you don't have the materials or you are too lazy to make one haha.

Step 10: Soldering and Connections to Audio Jack

-Make a bridge between the third transistor collector and the next pin from the female header, this is for connecting easily and audio jack soldered to male headers, like in the pictures, if you have any kind of audio jack different to this is recommended to google it to find out how pin are and make you own improvement.

-Time to get the precious sound from the air, that is needed to be listened by our ears, that's the point!

-Use any female 3.5 mm audio jack to connect the output that is located between the collector and the 3V positive rail, of course you can use the 1.6 v positive rail, but it will be less powerful than the other.

-Solder the 3V positive rail from the AA battery bay to the anode (positive) of the 1n4148 diode or pin 1.

-time to solder the left pin from the audio jack (mono audio) to the 3V volt positive rail, to the pin 1 of the female header or directly to the 3V positive rail from the AA battery bay, later i figure out that this connection could be shorter, but i don't wanna to cut the cable from the bay you know we are not rich haha.

-and the last connection is for the negative, that simply goes to the third pin of the female jack or any pin where you connected the negative rail from the circuit :)

Step 11: Working Video and Final Recomendations

-Well the time takes me to write, edit and upload this instructable is quite large but is for you! to entretaining from this crazy times, and to discover the other beautiful side of electronics (like amplifiers, digital, timers, and son on) this is the receivers, or tuners, the radio frecuency electronics. very interesting fro many hobbysts and radio amateurs entering to this world.

-in case you want to view a full video of this thing working you can see here:

-it is in Spanish because i'm from México, yeah that part of the world where D.T. wants to build the wall, and we are not all bad hombres as you see, i only want to know Berkeley University and San Francisco Bay Area, that my dream :)

I hope you like this instructable and video, if you like it don't forget to share, like and suscribe to my YouTube Channel where i publish content frecuently www.youtube.com/electromanmx

See You Soon, Good Bye!