simple am transmitter

Simple AM Transmitter

Description

Here is the circuit diagram of a simple AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs.You will love this!.The circuit has two parts , an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz. These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again. The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground. Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5.

Am Transmitter Circuit Diagram with Parts List.

Am Transmitter Circuit Diagram

http://www.circuitstoday.com/wp-content/uploads/2008/04/am-transmitter1.JPG

Notes .

The transmission frequency can be adjusted using the variable capacitance C3. Use a 200uH inductor for the L1 in the tank circuit. Power the circuit using a 9V battery for noise free operation. Use a 30 cm long insulated Copper wire as the antenna.

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Tags: hobby projects, Most Popular Circuits, Radio Circuits, Simple Electronics Projects, Transmitter

61 Responses to “AM Transmitter circuit”

1. samuel says:

August 6, 2008 at 3:22 am

Good day!

Can you please give me instructions on how to make the L1 inductor with the value 200uH?

This would be a very big help…Thanks

sam

2. Wolf -LM says:

August 13, 2009 at 5:57 am

if u have 2 100Uh you could add them in parrallel

3. rhea coros says:

August 28, 2009 at 11:53 pm

hello…is it ok to use a 5K variable resistor instead of a 4.5K?

thanks…

4. rhea coros says:

August 28, 2009 at 11:55 pm

hello…

is it ok to use a phone plug instead of a microphine…

thanks…

5. admin says:

September 4, 2009 at 5:19 am

you can use 5K instead of 4.5K

6. thaer says:

November 2, 2009 at 8:10 am

thank u

7. M.-E. says:

November 5, 2009 at 1:04 pm

Hi!Some Qs:1. i don’t have a cond.-mic. -how do i do to use an mic. wich is build with a magnet and a coil? (i don’t remember it’s name right now)2.how strong is this transmitter?(in watts)3.if i don’t have the transistors bc109 -witch other can i use?4.how do i do to make this transmitter stronger?-Thank you!

8. M.-E. says:


Forgot:5. how do i do to connect some sound-sorce like a cd-player or my computer to the transmitter?

9. ED says:


hi men , thaks for the diagram , you saved my ass XD i want to ask ou something , how could i build that inductor ? do you have some manual , i have the problem that here in my city electronic stores are very bad so they dont have any inductor XD

Saludos desde México , oaxaca jejeje

sorry for the grammar mistakes lol

ED…

10. kurimaw100 says:

December 16, 2009 at 5:17 pm

hello.. I cant find a bc109c transistor do of any alternative transistors? Tnx

11. kurimaw100 says:


hello.. I cant find a bc109c transistor do you know any alternative transistors? Tnx

12. admin says:


Other options are BC107, BC548,BC148, 2N2222 etc.

13. admin says:

December 17, 2009 at 4:46 am

The approximate inductance of a single-layer air-core coil may be calculated from the simplified formula:L = (d²n²)/(18d+40l)where:L = inductance in uH,d = coil diameter in inches,l = coil length in inches, andn = number of turns.This formula is a close approximation for coils having a length equal to or greater than 0.4 d.

14. admin says:


You must remove R9 and condenser mic. The sound source can be connected across to the base of Q1 and ground. A coupling capacitor of 10uF must be also added to the base of Q1.

15. Seetharaman says:


For L1 I have used 77turns of 28SWG enameled wire wound side by side on a 5/8″ dia 8″ ferrite rod. The audio quality is good. C6 I have increased to 220 mfd which improved the audio quality. Also I used 10uF for C5.

16. MSHELIA says:

January 5, 2010 at 1:17 am

HI, I AM GRATEFUL FOR THE CIRCUIT DIAGRAM OF AM TRANSMITTER I GOT FROM YOUR SITE BUT COULD YOU FURTHER HELP ME WITH THEIR ANALYSIS AS WELL? I WILL BE GLAD IF YOU DO. THANKS

17. suresh says:

January 12, 2010 at 10:25 pm

Does this ckt diagram works?

18. suresh says:

January 12, 2010 at 10:28 pm

we have a problem on making l1 inductor.can u help?

19. Walid says:

January 15, 2010 at 11:55 am

How does the AM modulation occur in this circuit ?

20. nav says:

February 1, 2010 at 6:56 am

in d formulaL = (d²l²)/(18d+40l)

where is the n used????/

21. Ehab says:

February 11, 2010 at 1:18 pm

I thank you about your circuits

22. rahul says:

March 3, 2010 at 4:48 am

hiiiii a really good circuit diagram for a am transmiter…. but i have a big problem that how to make a 200uh inductor can u help me on this .give me the procedure for it . plzjust send it on my [email protected]

its really urgent for mei hope u will help me…….

rahul

23. admin says:

March 4, 2010 at 5:04 am

Reply to rahulThis article will help you http://www.circuitstoday.com/how-to-make-an-air-core-inductor

24. john says:

March 4, 2010 at 8:55 pm

@ SureshTry this linkhttp://www.circuitstoday.com/how-to-make-an-air-core-inductor

25. john says:

March 6, 2010 at 2:20 am

Reply to navThis article will help you http://www.circuitstoday.com/how-to-make-an-air-core-inductor

26. nikiforos d. says:

March 12, 2010 at 8:46 am

Circuit Description :———————*From THE NEGATIVE POLE connect via a 10 k /1/2 watts RESISTOR TO THE “C” of the transisor* a 2 N 2222 SILICON n-p-n transistor.

Initially the ” b ” OF THE transistor to be left open .

THE ” E ” OF THE TRANSISTOR CONNECTED TO THE ( + )OF

THE BATTERY .

a stronf a.f. oscillation occurs, traceable throuch 2* 32 ohm via a 0.1mf fix capacitor.

we may use crystal earphone but output very stong ,*danger for ears *, feels a series volume control with one the earphone leds absolutely nessecary e.g 50-100k.

YES THE POLARITY IS REVERSED ,THE TRANSISTOR WORKS IN UNUSUALL mode /WORKS AS A spasistor IN A RELAXATION BEAK-DOWN MODE LIKE A U.J.T.

I DIDNT HAVE ACCESS WITH OTHER TRANSISTOR TYPES

LIKE E.G. BC 109 ETC….///

HAPPY EXPERIMENTATION —NIKIFOROS D. /GRECE./ATHENS.///*we may experiment with E CONNECTING IT TO C OR E ALWAYS THROUGH PROTECTING CAPACITOR AND /OR RESISTANCE.


March 12, 2010 at 11:24 pm

Hi Niki could not make out head or tail. pl give the details of the circuit on which you have commented

28. Alvaro says:

March 23, 2010 at 5:47 pm

Hello, this circuit is just perfect for a project I’m working on, but how can I increase the power output so that the signal will be able to penetrate a thick brick wall? Don’t worry about any legal issues,as my country allows the use of equipment like this for purely academic purposes.

Cheers,Alvaro

29. Alvaro says:

March 28, 2010 at 4:46 pm

Also, how can I adjust the circuit to transmit an empty signal. In other words, how can I adjust it to transmit a signal with no modulation and constant amplitude, so that any radio would just play an empty constant sound. Is it enough to just remove the condenser mic from the circuit, or are other modifications necessary. One more thing, I could only get 10 nF capacitor for C2, will the circuit still work? If not, is there any way to compensate for it?

Thanks for the help,Alvaro

30. seetharaman says:

March 28, 2010 at 8:25 pm

Hi the power can be increased by adding further RF power amplifier(complicated). a little increase can be done by raising power supply to 12volt and changing Q2 to 2N2219 with cooling clip and reducing emitter resistance to 470 ohms . By increasing C2 to 10n, you are likely to loose little HF response in the modulated Audio. By Disconnecting C1, only the carrier will be produced (blank carrier without information) sufficient to interfere

with the nearby receiver not allowing it to receive the required signal (by jamming it & brick wall is not a problem for HF).

31. snehal says:

April 13, 2010 at 8:50 am

what value of variable capacitor c3 should i use to obtain transmitting frequency of 500khz?

32. seetharaman says:

May 15, 2010 at 9:23 am

Hi Snehal with 500PF you will tune to 500KHz with 10 to 50 PF you will tune to 1500KHz. Higher the capacitor lower the frequency lower the capacitor higher the frequency.

33. Fisch'e says:

May 23, 2010 at 2:43 am

just got the circuit i hunted almost year round and thank u so much. So my problem is how would i interface with PIC to send morse code using AM band.you can just inbox me…[email protected]

34. mulla says:

September 4, 2010 at 11:07 pm

your formula does not have n number of turns of coil.can you explain?


September 18, 2010 at 9:16 am

Hi Mulla kindly refer to ADMIN reply on dec 17th

36. hassan says:

October 3, 2010 at 10:43 am

readers are leaders

37. linta says:


sir plz tell me the range for the circuit?plzcan it be increase by using larger wire?plzzzzzzzzi am waiting?



Hi Linta the range may be between 100 to 200 ft. You can use a roof top diagonal antenna of 100ft in length with (seven strands wire)the transmitter.as such you can improve the power by shifting the battery from R8 Mic end to R8 RF transistor end.

39. M.-E. says:

October 12, 2010 at 10:50 am

Hi!If i wanna make this one for 12 volts -wich resistors, etc. shuold i use?Thanks!/M-E



Hi M-E no change is required except the one suggested on 9th october.

41. bari says:


Please tell me if this circuit is designed on bread board, how much its stay capacitance matters? Is it can change the frequency and through the transmission out from the band?Reply..Waiting……



Hi Bari Being a MW frequency circuit the stray capacitance should not matter anything.

43. BARI says:


Thanks Seetharaman!! Its working! now i am going to sold it on vero board! Any suggestion?



HI BARI you can use vero board. my proto was only on a veroboard. now dotted boards are available you have to link them with copper wire. that is good for even HF application.

45. Michael Bitter says:

February 8, 2011 at 7:04 pm

If I wanted to transmit a signal to 58KHZ and using the formula of Fr= (1/2pi*sqr(lc)) which would give me a C3 of 500PF and a L1 of 15mH. Is there anything else that I would need to do to the circuit to work at this frequency? Thank you.

46. Bale says:

March 1, 2011 at 5:36 pm

HiI was wandering if C2,C4,C1 are ceramic caps or electrolytic because they do not hve the + sign on the clr.

thanks


March 1, 2011 at 10:31 pm

Hi Bale C2 & C4 are ceramic disc capacitors. C3 is a variable capacitor. C1 is electrolytic, positive terminal is to be connected to potentiometer R5.Hi Michael you may have to increase C4 by trial and error to get the circuit into oscillation. no other change is required.

48. chavan priyanka pratap says:

March 3, 2011 at 5:41 am

Good day!

Can you please give me instructions on how to make the L1 inductor with the value 200uH?

This would be a very big help…

49. Dadirac7 says:

April 14, 2011 at 12:51 pm

Hi: I’m building the AM transmitter and I want to use it in 1460khz. Can I use a variable capacitor 10-50 uF, for C3? Is it posible really to use two 100uH RF Chokes in series to get 200uH for L1? Is there a diferent name for variable capacitor? I can’t comunicate with the people at Radio Shack or do I have to get it (variable capacitor) by mail?


April 15, 2011 at 7:00 am

Hi Dadirac7 use a 15mm plastic former (PVC Tube)and close wind 100 turns of 32SWG wire (do not over lap, wind side by side without any gap) use 10 to 50PF variable trimmer to tune to high end of MW band. To tune to lower end of MW you require 500PF.

51. Dadirac7 says:

April 18, 2011 at 8:36 pm

Hi Seetharaman:Thanks to you I’m in tune. My question now is, whats a cooling clip? Like a heat sink atached to the transistor? I want to increase my transmiting range, can we do anything to the antenna?


April 19, 2011 at 8:49 am

Hi Dadirac7 cooling clip is clip on heat-sink used for T05 T018 packages.First shift positive of the battery to C2 R6 side of R8. This itself will increase the power. for further increase replace Q2 with 2N2218 or 2219, raise the battery voltage to 12 volt.

53. MRelectro says:

May 7, 2011 at 10:43 am

HiI just simulated this circuit using PSPICE

then I couldn’t find clean amplitude modulated signal.

I used Vsin (Offset = 0, amplitude = 1mV, Frequency = 1kHz) rather than cond mic

and I set the 4.7k potentiometer parameter (set = 0.5).

I didn’t connect the anntena and just connect voltage marker to that node. other setting is identical to the diagram.

The simulation result was distorted sine signal (I couldn’t find out any carrier frequency)

Is there any problem I did?

54. Azim says:

May 10, 2011 at 12:35 am

Sir,I am a first year new Electrical & Electronic Engineering student. Please tell me what the volt of C1,C,C3,C4,C5,C6. And you tell me how I understand the capacitors Voltage….Please please…


May 10, 2011 at 3:46 am

Hi Azim all capacitors are to be rated for 12 volts or higher. Capacitor voltage will be written on the capacitor itself. if not with colour code or any alphabet refer to manufacturers catalog.

56. Azim says:

May 10, 2011 at 10:46 am

Thank you Sir, But I Tell How I Understand The capacitors Voltage to The Circuit Diagram Where Not given The Voltage(Ex:C1: 2.2uF).Please Tell Me Any Website or PDF File Which is Help Me.


May 11, 2011 at 1:09 am

Hi Azim if the supply voltage is 12volts DC ensure all capacitors are rated for 16 volts or more on the safe side. This is the simple thumb rule.

58. amanuel says:

May 11, 2011 at 10:41 am

Thank you sir,But How the potentiometer works with the AM transmitter!!!

59. EL says:

May 12, 2011 at 5:51 am

I just simulated this circuit using PSPICE

then I couldn’t find clean amplitude modulated signal.

I used Vsin (Offset = 0, amplitude = 1mV, Frequency = 1kHz) rather than cond mic

and I set the 4.7k potentiometer parameter (set = 0.5).

I didn’t connect the anntena and just connect voltage marker to that node. other setting is identical to the diagram.

The simulation result was distorted sine signal (I couldn’t find out any carrier frequency)

Is there any problem I did?

60. dan12 says:

May 14, 2011 at 6:49 am

Plz, tell me how the amplified signal from Q1 and carrier signal from tank circuit could be modulated by Q2. I can’t understand the physical principle.

61. komal says:

May 18, 2011 at 10:05 pm

Is this the perfect,simple & suitable circuits for am transmitter?

Read more: http://www.circuitstoday.com/am-transmitter-circuit#ixzz1SWywpUxN Under Creative Commons License: Attribution

This circuit can transmit AM radio wave in MW frequency of around 600 Kilo hertz.

The circuit uses a power of 9 voltage and around 100 mili amperes. You can use a 9v battery for the power supply.

The Timer IC 555 is used a free running multi vibrator which have been adjusted in frequency of 540 Kilo hertz.

The sound signal is inputted to pin number 5 of IC from the condenser mic. And The IC converts the signal to a Amplitude modulated frequency and outputs from pin number 3 from which an Antenna of length of around 2-3 meters converts the frequency to radio waves which can be received by any Medium Wave radio receiver by tuning it to around 600 Kilo Hertz from a distance of up to 25-30 meters.

You can also make the transmission frequency of this circuit variable by using a Preset Resistor instead of R2 and a Gang condenser instead of C1.

Parts list:

Resistance: Value:

R1 380 ohms.

R2 1 Kilo ohms.

Condensers: Value

C1 0.001 Micro farad

C2 1000 micro farad / 25 volt.

Semiconductors:

IC1 Timer IC 555

Others:

Condenser Mic.

An antenna or wire of length around 2-3 meters , printed circuit board, 9v battery Etc.

Circuit Diagram:

Click on the image to enlarge it.

http://justtechnika.com/wp-content/uploads/2010/10/simple-digital-Am-transmitter-circuit-diagram.jpg

simple digital Am transmitter circuit diagram.

1. http://www.zen22142.zen.co.uk/Circuits/rf/amtx.htm 2. http://justtechnika.com/articles/circuit-diagram-simple-digital-am-transmitter/ 3. http://www.extremecircuits.net/2010/05/simple-am-transmitter.html 4.

http://www.extremecircuits.net/2010/05/simple-am-transmitter.html

http://justtechnika.com/articles/circuit-diagram-simple-digital-am-transmitter/

http://www.zen22142.zen.co.uk/Circuits/rf/amtx.htm

simple am transmitter

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