The following circuit was taken from an old electronic book, it is indeed a very nice little two transistor radio receiver circuit which utilizes very few components yet is able to produce output over a loudspeaker and not just over headphones.
Circuit Operation
As can be seen in the given circuit diagram, the design is as simple as it can be, just a couple of general purpose transistors and a few other passive components for configuring what looks like a nice little AM radio receiver unit.
The circuit functioning is pretty basic. The antenna coil collects the MW signals present in the air.
The trimmer sets and tunes the frequency which needs to be passed across to the next stage.
The next stage which comprises T1 functions as a high frequency amplifier as well as a demodulator. T1 extracts the audio from the received signals and amplifies it to some extent so that it may be fed to the next stage.
The final stage employs the transistor T2 which operates as a simple audio amplifier, the demodulated signal is fed to the base of T2 for further amplification.
T2 effectively amplifies the signals so that it becomes audible over the connected speaker loud and clear.
T1's emitter has been configured as a feedback link to the input stage, this inclusion greatly enhances the performance of the radio making it extra efficient while identifying and amplifying the received signals.
Circuit Diagram
Parts List for a simple 2 transistor radio receiver with speaker
- R1 = 1M
- R2 = 22K
- R3 = 4K7
- R4 = 1K
- P1 = 4K7
- C1 = 104
- C2 = 470pF
- C3,C4 = 10uF/25V
- T1 = BC547
- T2 = 8050 or 2N2222
- L1 = ordinary MW antenna coil
- SPEAKER = small earphone 10k
- TRIM = ordinary GANG
MW Antenna Coil on Ferrite Rod (L1)
Use the Following type of GANG Condenser for the Trimmer (use the center pin and any one of the output pins from the MW side)
Simple AM radio Circuit using FET
Despite having so few parts, the following little AM broadcast band receiver circuit operates astonishingly well.
It is possible to remove the tuning coil [L1] and capacitor (CV11) from an obsolete transistor radio; L1 is the loopstick antenna.
In order to produce a sound across R2, a JFET, Q1, is utilized as a high impedance source-follower, directly connected with transistor Q2, which is employed here as an amplifier and collector-bend detector.
The transistor's collector characteristics provide the necessary rectification of the signal.
The rectified RF is bypassed by C1. C2, which is ideally of the tantalum type, bypasses the emitter bias resistor R3 of Q2 for optimal performance.
For excellent sound output levels, use high impedance headphones.
A 9 V transistor radio battery may be used to power the circuit.
Simple High Performance MW Receiver Circuit
An Improved version of the above Medium Wave radio can be studied in the following paragraphs. Once built it can be expected to work immediately without any hassles.
The MW receiver works with four transistors.
The first transistor is configured to work in the reflex mode. This helps just one transistor to do the job of two transistors which results in a much higher gain from the design.
The working efficiency may not be as good as a superhetrodyne, nevertheless is just enough for a good reception of all local stations.
The transistors can be BC547 and BC557 for the NPN and the PNP respectively, while the diode can be 1N4148.
The Antenna Coil could be built using the following data:
The ferrite rod antenna coil picks up the AM frequency through the tuned network of C2, L1. The tuned AM signal is fed to the first transistor TR1 via L2.
This enables a correct matching of the high impedance input from C2, L1 with the transistor input, without causing any deteorioration of the tuned signal.
The signal gets amplified by TR1 and is fed to the detector stage made using the diode DI.
Here since the 470pF capacitor C4 responds with a lower impedance to the incoming r.f. (radio frequency) than the 10 kilohm resistance R4, implies that the signal is now forced to enter through the capacitor C4.
This filters out the audio element in the signal after D1 detection, and is sent through the R2, L2 stage to the base of TR1.
C3 eliminates any form of stray RF.
Next is C4, which offers a high impedance to the signal compared to R4, which prompts the signal to move to TR2 base.
Audio Amplifier
Transistors TR2, TR3 and TR4 work like a push-pull amplifier.
TR3 and TR4 behave like a complimentary output pair while TR2 functions in the form of a driver stage.
The pure audio signal extracted from TR1 is amplified by TR2. The amplified positive cycles of the audio signal feed the TR4 through D2 while the negative cycles are sent through TR3.
The two signals are eventually combined back using C7 after the amplification process is completed. This finally produces the required output audio MW music over the loudspeaker LS1
The next MW or AM receiver is actually so easy that really tiny expenditure is necessary for its construction, and as just a few number of parts are employed it is ideally suits a mini radio receiver, that effortlessly accommodates inside a shirt pocket.
Even so it provides very good reception of nearby radio stations with no need for an external antenna or earth wire.
Functioning of the receiver is extremely straightforward. Transistor T1 works like an r.f. amplifier and detector with regenerative (positive) feedback. The level of feedback, and therefore the sensitivity of the MW receiver, could be manipulated by varying P1.
Even though output to the base of T1 is obtained straight from the upper section of the tuned circuit L1/C1, instead of through a coupling winding, the impedance offered by T1 is quite enough to make sure that the resonant circuit is barely suppressed.
Because the current gain of T1 decreases on the higher frequency side of the spectrum, while the input impedance rises, the gain of this stage continues to be relatively consistent on the entire spectrum, in order that it is normally not essential to fine-tune P1 often.
Signal detection happens on the collector of T1 and the output impedance of this T1 stage and C3, cleans out the r.f. portion of the rectified signal. T2 supplies further amplification of the a.f. Signal to operate the attached crystal earpiece.
PCB Layout and Construction Details
Construction An extremely stream-lined PCB layout is shown below for the proposed AM receiver. L1 must be positioned as near as is possible to the PCB surface to prevent oscillation issues.
Individuals who want to miniaturize the layout even more may try things out by decreasing the measurements of the ferrite rod and adding more number of winding to obtain the very same inductance, while in case L1 is built smaller an external antenna could be required, which could be attached on the upper terminal of L1 through a 4.7 p capacitor.
The proposed dimensions for L1 will be 65 turns of 0.2 mm (36 S.W.G.) enameled copper wire over a 10 mm diameter 100 mm long ferrite rod, with the center tap coming out at 5 turns away from the `ground' end of the antenna coil.
C1 could be a small (strong dielectric) 500 pF gang condenser, or to get signals from a single fixed station only it might be substituted with a permanent capacitor of just lower than the necessary value in parallel with a 4 to 60 pF trimmer.
This may make it possible for the dimensions of the MW radio receiver to become additionally minimized.
Last but not least, the working current of the receiver is incredibly minimal that around 1 mA) in order that it will probably run for many months with a PP3 9 V battery.
Capturing Unwanted AM Radio Signals
The circuit displayed below is a tunable AM signal trap circuit which can be controlled to retrieve unwanted AM signals and channel the remainder to the receiver.
Inductor L1 is used as a broadcast loopstick-antenna coil whereas capacitor C1 is set for tuning. You can easily get these components from an old radio.
If the interfering signal comes from the lower frequency side of the broadcast band, you need to set L1’s slug around ¾ of the way into the coil and adjust C1 for a minimum signal output at the interfering frequency.
Once the interfering station’s frequency is close to the upper end of the band, regulate the slug until the end of the coil and tune C1 until you get a minimum signal.
It can happen that some unwanted transmitter signal besides a typical AM-broadcast type waves can get into the tank circuit.
When that happens, you must find out the transmitter’s frequency and choose a coil/capacitor arrangement that will resonate at that frequency. Then, connect that combination to the schematics above.
AM Signal Extractor
The following design is a frequency-selective circuit that be replaced for a LC tank discussed above.
When the expected signal can be detected but masked with noise, this circuit does the ‘unmasking’ tasks and delivers the signal to the receiver via the tank circuit.
When the tuner is boosting the required level for the frequency, it is also suppressing all other signals outside its passband. You can easily use the same combination of values for the capacitor and coil as depicted above..
Other kinds of antennas and selective circuits can be evaluated through the input of this tank circuit.
A huge tuned loop will provide the circuit an option to help reduce an interfering signal arriving from diverse directions.
If there isn’t space for a big loop, you can opt for a large, tune ferrite coil as a replacement and hold its feature.
AM Booster Circuit
The above AM signal tuner circuits can be effectively attached with the signal booster circuit below for creating an enhanced antenna system for any AM radio.
You just have to connect the arrow head side of the above explained LC circuits with the gate of the FET Q1 in the below shown circuit.
Another Simple AM Radio Antenna Booster Circuit
The following AM booster circuit can significantly enhance poor AM broadcast reception if that is a problem for you.
It is a four stage wideband amplifier with a high impedance input that may be used with a modestly sized vertical whip antenna.
The antenna is directly connected to the Q1 JFET in the first stage's gate.
This stage was built for a high input impedance because short whip antennas exhibit a high feedpoint impedance.
The AM radio signal at the source flows through C3 to the base of Q2, which functions like a common-collector stage.
Q1 is configured like a common-drain stage. Effective input-output isolation is provided by this configuration.
In the next stage, Q3, which functions as a common-emitter amplifier, is directly connected to Q2's emitter.
Its collector is directly linked to the common-collector emitter follower amplifier Q4's base. The signal is capacitively linked through stage C9 to deliver an impedance-low output.
Due to the splitting of load resistance and Q4's bypassing of the split load resistance, only a portion of Q2's collector load is active at RF.
Due of the circuit's minimal electricity consumption, a transistor radio battery is used to power it.
TRF MW Receiver
Image of the Built TRF Receiver Prototype
The antenna coil L1, the capacitor C1, and the diode D1 form the TRF MW receiver circuit or the main tuned receiver circuit stage.
C1 is a varicap diode whose capacitance varies depending on the voltage across it.
When the P1 is varied, it causes a voltage variation across C1, which in turn causes the tuning of the receiver and catching a various radio frequencies depending on the resonance formed by the C1 and L1.
Therefore varied P1 of the TRF receiver circuit allows to select the desired stations from the available incoming MW bands.
T1 and T2 along with the associated parts form the demodulator and the preamplifier stages, where T1 demodulates the resonant tuned frequency from the L1/C1 stage such that only the audio section is allowed to pass while the other unwanted voltages are blocked.
This tuned audio signal is fed to the preamplifier stage formed by T2 and the associated parts.
The pramplified radio audio is sent to the base of T3 via P2 and C6. P2 helps to set the volume of the output, and therefore works like a volume control pot.
The transistor T3 further amplifies the audio signal and forwards it to the power amplifier stage built around the transistors T4 and T5.
The T4, and T5 stage along with the other associated component form a nice little 1 watt transistorized amplifier that sufficiently amplifies the TRF audio signals, and feeds it to the attached loudspeaker.
The tuned MW radio output is thus effectively reproduced on the speaker loud and clear.
MW Radio Circuit using IC 4011
The circuit demonstrated below can be used like a simple MW receiver structured around the 4011 CMOS IC.
The four gates inside the 4011 IC package are configured as linear amplifiers by hooking up their inputs one after the other and by creating a negative feedback.
The antenna coil L1, can be built by tightly winding 80 turns of 22 SWG enameled copper wire over a 3/8" diameter ferrite rod, and this works like the pickup coil.
The L1 is tuned through the 500pF trimmer and tank circuit tus formed is referenced to earth at the radio frequency by C1.
The high input impedance, offered by IC1/1, provided to the tank circuit guarantees that the damping factor is kept to the minimum, which causes the MW receiver circuit to be highly selective.
The output from the IC1/1 geneartes an amplified RF signal which is transferred to IC1/2 for the detection function.
The unwanted RF frequency generated at the output of the detector is eliminated by the low pass filter created by resistor R4 and capacitor C2.
The output audio signal is subsequently provided to an amplifier constructed around IC1/3 and IC1/4.
The current consumption of the MW radio circuit's is around 10 mA while powered through a 9 V supply.
Remember that the IC used in this design has to be a 4011AE and not the 4011B whose input protection circuitry could prohibit it from running in the linear mode.
Super Regenerative Radio Receiver
The next circuit depicts our final receiver circuit, which is a solid-state adaptation of Major E.H. Armstrong's well-known regenerative receiver.
The regenerative receiver ruled throughout its age in radio history and did so until the Major introduced his superheterodyne receiver circuit.
The majority of modern commercial radios are designed using the fundamental superheterodyne architecture.
The antenna coil L1 has 50 turns of 22 SWG super enameled copper wire over a 3 inch long former having a diameter of 2.5 inches.
The other coil with 6 turns in wound over the 50 turns of L1, with a layer of insulation tape in between.
In order to reduce the stress on the tuned circuit, the two BC547 transistors are coupled in a Darlington high input impedance circuit topology.
Tuning the desired radio stations is carried out by C3 and C4. The positive RF feedback is controlled via potentiometer R2. The regeneration control, which also controls the receiver's audio output, is more usually referred to as a potentiometer when it is used in this manner.
In case the receiver seems unresponsive and only faint signals are being received, consider swapping the 6-turn feedback coil's terminals.
That could be all that's required to make the circuit fully functional and active.
Questions & Answers
can we seperate a smartphone mobile screen from its circuits making it wireless?its for a project.
no that won't be possible..
Hi Tanmay,
The overlapping broken lines suggest that these are NOT connected. The connected lines are shown with a black dot.
P1 is a preset which has three leads, the center lead is indicated with a arrow head.
As suggested by Mr. Shane, you can replace R3 with an small audio output transformer.
The primary winding which has three wires should be connected in place of R3, while the secondary must be connected with a speaker.
104 = 0.1uF
T1 can be replaced with BC548, but T2 should be 1amp rated, any transistor rated at 1amp will do like 2N22222 etc.
L1 should be a readymade MW antenna coil, any other type won't produce correct results
1)Try BC557
2)You can try winding it on any small ferrite former. Wind 1000 turns of 32 to 36 SWG wire, and over that 8 turns of 27 to 32 SWG wire.
3)small RF chokes are definitely available in market.
IF trafo specs can be entirely different for different sages so it can be very difficult to set them correctly.
You can find plenty of radio repairing guides online, just type the relevant keywords and Google it.
Thanks! Yes surely it can be done, you can the take the pickup to the amplifier from across C4 output and ground
Hi Tanmay,
Here's the formula:
XL = ωL = 2piFL
where XL is the inductive reactance, ω is the angular frequency, F is the frequency in hertz, and L is the inductance in henries.
Inductive reactance is the positive component of impedance. It is measured in ohms.
You can use 4060 IC for making a simple timer
Regarding the 810 circuit I can't say much without actually seeing it.
which circuit are you referring to?
Anyway, yes definitely all trafos with prim/sec stages will have specific winding arrangements.
yes the winding will have definite start and finish points, the primary from up to down, while the secondary from down to up or vice versa.
recheck transistor polarity and antenna coil polarity, and connections.
Under normal conditions no antenna is required for this circuit.
yes that can be done, you can incorporate a 7809 regulator for better response.
how do you add a variable tuning capacitor
the component indicated as TRIM is the variable tuning cap.
1) There is an earthing symbol. How to earth in a circuit board?
2) Can I use 8ohm/ 0.5watt speaker?
1) earth symbol refers to supply negative line
2)8ohm/0.5 watt will do.
i know R1 , R2 are resistances, but what signifies for R3=4K7? P1=4K7?
they have been calculated and placed for making the transistors conduct optimally as per the circuit specifications.
i mean , what i have to tell to the shopkeeper to buy? will he understand by "4K7"?
4k7 means 4.7k, you tell him you need a 4 point 7 kay resistor.
Hi there sir Swagatam!! I have a few questions:
1. What is the range of the radio(in KHz)?
2. Area all resistors 1/4 watt?
3. What kind of capacitor is c1 and c2? (I think they're ceramic?..just guessing..)
4 Are c3/c4 an electrolytic capacitor?
5. Is p1 a volume control?
6. Is there a proper specs for trim capacitor, like something to tell the salesboy/girl in an electronics store?
Thanks a lot!!! (apologies for those silly questions of mine…)
Hi Eshkariel,
The range is the same as we normally have in all MW radios.
all resistors are 1/4 watt
C1/C2 can be ceramic.
C3/C4 are electrolytric
p1 is a kind of volume control
trimmer capacitor can be a normal MW GANG condenser
umm…excuse me Sir do you have some good topic here to start for robotics?…just inquiring..Thanks…
sorry, I have not yet started anything related to robotics in this blog
HELLO SIR.what is the transistor 8050.There is any symbol before it like bc,2sc.can i build it in a veroboard. also can i use a gang from very old transistor radio made of metal
Hello Dibya, the prefix can be anything, it's not important, the number 8050 is the only unique assignment and you can tell this number to the retailer while buying it.
yes a radio gang will do
Thank you sir. My house is about 100km away from radio station .Does this work for me.
No, 100km is too far away, this radio will not work from this distance.
Sir can i use 1895 IC audio amplifier to make the sound louder.
Thank you very much sir . For your fast response
Sir please publish a MW signal booster.
I had made many 6 transistor radio , 7 transistor radio and also 8 transistor , ic based 5band radio but two transistor radio is first time in my life.
sure, if possible i'll try to post it…
sir plz tell me . Ac 128 transistor is available in Indian market.
My grandmother's radio need to be repaired
Dibya, you can use BEL188 if you don't find AC128, but AC128 should be available.
Where can i add antina in this circuit
the antenna coil can be procured from any local electronic spare part retailer.
in the diagram there's a symbol of variable capacitor but it said trimm…can you please clarify me about it, im working on this circuit…thanks
a variable capacitor is also referred to as a trimmer…but it's a PCB mount type not the Ganged type…although a GANG cap will also work equally well.
can you please post a picture of it, coz i think the man from the electronics shop gave me the wrong one….thanks a lot
Picture of trimmer :
Picture of Gang:
thanks a lot…it really helps
…what's the pin configuration of the 3 pin variable capacitor? (the square one).. thanks
use the center pin and any of the outer pin in the line…there will two sections for this, don't use the FM section, use the AM section….
…i have another question C2 is connected to the ground and is it connected to R2? also R1 is connected to the coil and is it connected to the emitter of T1?.. thanks
the cross link connections are shown with a black dots….the cross links which are not connected are shown with white gaps….so the ones which are not connected with a black dots are unconnected with each other.
R1 is Not connected to T1 emitter
…hello what is P1? is it a resistor?
then C2 is connected to the ground only?
another thing is that is the base of T2 connected to P1? and by the way is P1 a resistor?
C2 is connected to ground and R2 junction.
T2 base is connected to R2 and T1 collector, P1 is connected to T1 emitter
P1 is a variable resistor, a preset
…i have another question, why did you use a NPN transistor and not PNP?, and why MW antenna coil?…thanks a lot….
NPN transistors are ideally recommended for all relevant circuit applications, PNP are just complementary and are used only when there's no other option left.
MW antenna is used because the design is for receiving AM signals not FM signals
the variable resistor, is the center pin connected to the emitter of T1?