AM Transmitter circuit
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 the 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.
Circuit Diagram with Parts List.
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.
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
if u have 2 100Uh you could add them in parrallel
hello…
is it ok to use a 5K variable resistor instead of a 4.5K?
thanks…
hello…
is it ok to use a phone plug instead of a microphine…
thanks…
you can use 5K instead of 4.5K
thank u
Forgot:
5. how do i do to connect some sound-sorce like a cd-player or my computer to the transmitter?
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…
hello.. I cant find a bc109c transistor do of any alternative transistors? Tnx
hello.. I cant find a bc109c transistor do you know any alternative transistors? Tnx
Other options are BC107, BC548,BC148, 2N2222 etc.
The approximate inductance of a single-layer air-core coil may be calculated from the simplified formula:
L = (d²l²)/(18d+40l)
where:
L = inductance in uH,
d = coil diameter in inches,
l = coil length in inches, and
n = number of turns.
This formula is a close approximation for coils having a length equal to or greater than 0.4 d.
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.
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.
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
Does this ckt diagram works?
we have a problem on making l1 inductor.can u help?
How does the AM modulation occur in this circuit ?
in d formula
L = (d²l²)/(18d+40l)
where is the n used????/
I thank you about your circuits
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 . plz
just send it on my id
rahul.bhandari71@gmail.com
its really urgent for me
i hope u will help me…….
rahul
Reply to rahul
This article will help you http://www.circuitstoday.com/how-to-make-an-air-core-inductor
@ Suresh
Try this link
http://www.circuitstoday.com/how-to-make-an-air-core-inductor
Reply to nav
This article will help you http://www.circuitstoday.com/how-to-make-an-air-core-inductor
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.
Hi Niki could not make out head or tail. pl give the details of the circuit on which you have commented
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
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
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).
what value of variable capacitor c3 should i use to obtain transmitting frequency of 500khz?
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.
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…matt.fisch@yahoo.com