Build AM FM Transmitter One Transistor Project 1-3

[1972bug2180]

What value of variable capacitor did you use? What if I just wanted to turn this into a A.M. transmitter? What variable capacitor could i use?

[AllAmericanFiveRadio]

@1972bug2180

You could use the variable capacitor from an AM radio, and the oscillator coil too.

[jks2]

ok thanks for the info!

[jks2]

i never build something like this before. nice little transmitter to start with. how far  (in meters) can this transmitter go? regards from the netherlands, jens.

[AllAmericanFiveRadio]

@jks2

Hey Jens,

This one, 1-3, works and would cover a room or two. 2-3 will cover most of the house. 3-3 covers about a block of the neighborhood. If you use an outside tuned di-pole antenna with 3-3 it will cover 1 mile=1609.344 meters easy.

[AllAmericanFiveRadio]

@ae4se

It is an NPN transistor from Radio Shack, 15 in a pack. Video T3-3 is a good design for an FM one transistor transmitter. Also The way I built it was not for looks. Part position at those frequency is very important, this is something that does not show in a wiring diagram.

[marioaleal]

Your website died!

[AllAmericanFiveRadio]

@marioaleal

Yes it did. I have called them and they had a major outage so they were not pick just on me. But while I was on hold for 15mins I thought I would make it worthwhile. I changed to a new server and transfered my domain name to the new server also. I had been on the old system for over 6 years, time to upgrade.

[marioaleal]

@AllAmericanFiveRadio THANK YOU. My son and I are going to try this project.

[AllAmericanFiveRadio]

@marioaleal

I hope you have fun and success with this project. I did three videos on this one transistor transmitter. T1-3, T2-3, and T3-3. Good luck!!

[mailomail]

This is the simplest transmitter I`ve ever seen and it works very good! I`ve build it and I`m very satisfied with the quality of the transmitted signal. It`s very clear. I have one question: How (where) to connect an external antenna to this circuit? I think.... the range of this transmitter would be much longer with an external antenna.

[AllAmericanFiveRadio]

Thanks mailomail

Glad you built it and it is working well for and thanks for telling the YouTubers.

I would use a DiPole and mount the transmitter in the center and run the audio to it. You will need to study up on DiPoles and wave length to determine the length of each wire. The ground from the transmitter goes one side and the output from the transmitter goes to the other wire of the DiPole.

[mailomail]

@AllAmericanFiveRadio

Thank you very much for the useful information. I will try it soon with DiPoles.

I want to thank you and congratulate you for this project. I really like your transmitter.

Best regards

mailomail

[AllAmericanFiveRadio]

Thanks mailomail

Hey Chris,

I think you will be pleased with an FM tuned DiPole. Please let me and the YouTubers know what the results are. This is going to be a very interest experiment.

Best regards,

Rick

[mailomail]

@AllAmericanFiveRadio Thank you very much Rick for your suggestions. I will make some changes (modifications) and I`ll let you know soon. I hope it will work very good.

Best regards

Chris

[AllAmericanFiveRadio]

@mailomail

The idea of the three video was.

1-3 is the original development.

2-3 good transmitter that covers the house.

3-3 the end result, covers the neighborhood plus. For a small radio FM license.

[mailomail]

@AllAmericanFiveRadio Thank you.

Today I`ve built this transmitter with your suggested modifications from T3-3 and it works great! I will have to check the range of it tomorrow. There is only one problem: The transistor gets quickly very hot. Is it normal? or something goes wrong? I`m afraid that it will burn out soon. I`m using BC338 transistor because I don`t have the suggested one.

[AllAmericanFiveRadio]

@mailomail

Glad it is working well. The heat I am not sure about. I am positive I ran it for four hour with out a heat problem. But I will be glad and check it again. I am positive we can get it right! I am using a cheep Radio Shack general purpose transistor. Cost about 10 cents. If you think it may burn out I would glue a heat sink to it.

[AllAmericanFiveRadio]

mailomail

Also make the MODs in T3-3 very important!!!!!!!!

[RadioDude1969]

Hi

Interesting video. I have two questions:

1) What is the reason for tapping the 3rd turn on the coil?

2) How could you change band from AM to FM so quickly?

Jon

[AllAmericanFiveRadio]

Thanks RadioDude1969

The 3rd turn supplies the power for the positive feed back from this point, and the lower coil through the 0.05uf cap to the base. This positive feed back keeps the oscillator, oscillating. This transmitter, transmits AM and FM simultaneously. So if you tune the transmitter to the AM band the AM radio will demodulate the AM and ignore the FM. Likewise if you tune the transmitter on the FM band the FM radio will demodulate the FM and ignore the AM.

[RadioDude1969]

@AllAmericanFiveRadio Thanks for the reply. Amazing how few components that are needed to build a combined AM/FM transmitter. But how could you change the frequency so quickly (between the AM band and the FM band) in the video? Since the coil is fixed, you must have to change the capacitor over a very wide range.

Jon

[AllAmericanFiveRadio]

@RadioDude1969

The variable capacitor has a large enough range.

[RadioDude1969]

@AllAmericanFiveRadio Sorry, I still don't get it; I have constructed a similar coil, and the inductance seems to be around 0.6 uH. If the tank circuit alone determines the oscillator frequency, this would require a 4 pF capacitor to resonate on 100 MHz. To resonate in the AM band, say around 1 MHz, it would require a different coil to use the same variable capacitor. I must be missing something here...I would really like to understand this, thanks for your patience!

Jon

[AllAmericanFiveRadio]

@RadioDude1969

This circuit will tune down into the AM band, but not with a high 'Q'. For that you should change the coil also. This circuit tunes in the AM, FM, old TV, Ham Radio 2meter bands and more. Pick the band you want to work in and then pick the vary capacitor and coil that is best for that band. This circuit is my temple that I use when I want to build a transistor oscillator.

[RadioDude1969]

@AllAmericanFiveRadio Ok, but is it the tank circuit alone that determines the frequency, or does the .001 uF capacitor in series play a role here?

Jon

[AllAmericanFiveRadio]

@RadioDude1969

I don't see a 0.001uf in series.

[RadioDude1969]

@AllAmericanFiveRadio The one between the tank circuit and the base of the transistor.

[AllAmericanFiveRadio]

@RadioDude1969

The 0.5uf is the positive feed back path. Has little influence on the tanks circuit.

[RadioDude1969]

@AllAmericanFiveRadio Ok, It's getting clearer how it works, but the capacitor in the diagram reads .001 uF (about 2 minutes into the video).

Thanks

Jon

[AllAmericanFiveRadio]

@RadioDude1969

LOL! Oh I was looking at the wiring diagram on the FM transmitter web page. But it is the same answer. In the video, the oscillator has a simple bias, the 100K resistor. On the web page the bias uses a resistor bridge, two 10K resistors at the point 1.1K negative to the positive point. This is why I can double the voltage on the web diagram and it work great. That is not the case for the video diagram.

[RadioDude1969]

@AllAmericanFiveRadio Ok, I got the feeling that we were not talking about the same circuit :-) By the way, I have built this transmitter, and it works well in the FM band. It acts a bit unstable, and I guess this is due to long leads. I will soon try to modify it for the AM band. Thanks again.

Jon

[AllAmericanFiveRadio]

@RadioDude1969

Yes, exactly right! The longer the leads the more unstable. That is exactly why I built the transmitter the way I did. Parts as close together as posable, very important for stability.

[nlimchua]

Hi Rick -

Question about the power supply. This circuit works using pure DC (battery). But it's either flaky or does not work using a regulated power supply. I'm assuming it has to do with the ripples (even a small ripple; <10mv p-p) on the dc converter? Can you confirm this? thx.

[AllAmericanFiveRadio]

@nlimchua

Yes, not using a battery and using a power supply may cause problems. You will need a highly filtered clean power supply.

[dodgedart74]

yea i couldnt get anything either.....

[AllAmericanFiveRadio]

You have to be very careful on how RF transmitters are constructed. RF would rather shortcut than travel through the air. Part location is important in RF. If you build the transmitter in the third video, exactly, you may be surprised. A YouTuber emailed me and said he was able to pick it up 3 miles away.

[CoolDudeClem]

HI, I just tryed built this circuit myself, but I couldn't receive anything on my radio that sounded like what I had connected up to it. Are there any other pointers you could give out that might preventing this from working?

[AllAmericanFiveRadio]

If this is you first transmitter build, which I remember mine very well, some things that seem minor are very important when you a deleing with RF. Example: one YouTuber could not get the Tube AM transmitter to oscillate. He was using black rubber washers for an insulator. The black color comes from carbon and was shorting out the RF.

[AllAmericanFiveRadio]

You have to be very careful on how RF transmitters are constructed. RF would rather shortcut than travel through the air. Part location is important in RF. If you build the transmitter in the third video, exactly you may be surprised. A YouTuber emailed me and said he was able to pick it up 3 miles away.

[nlimchua]

@AllAmericanFiveRadio Rick - for this project, is the capacitance range of the variable capacitor? I built this, works but quite unstable (I'm suspecting due to a cheap variable cap that I pulled off of an old transistor radio). Also, would there be any difference in using a 24 awg magnetwire for the inductor? Looks like you used a non-copper for yours. thx.

[AllAmericanFiveRadio]

@nlimchua

In the diagram it shows 0.1-0.5 nf and a 0.5nf in parallel. It is very important to keep all the connecting leads as short as possible. The longer the leads the more unstable, that is why I built the transmitter the way I did. As long as have the gage of wire is close it should work, I designed the coil so the gage is not super critical. But having the coil and tuning capacitor as close together as possible is critical.

[togst]

Interesting project, simple and looks stable! I will definitively have to try it out. Changing between AM and FM is as simple as changing the connections between AM/FM on the variable capacitor? And would any transistor that can handle the FM frequencies suffice? Would connecting and antenna to the collector side and increasing the voltage increase the transmitting range?

-Frank

[AllAmericanFiveRadio]

Hey Frank,

I am using a general purpose NPN transistor. It came in a box of 30 or so, probable cost 10cents. The way I am modulating it, there is an AM and FM component at the same time. So the AM radio detects the AM MOD and ignores the FM. The FM radio detects the FM MOD and ignores the AM. I was hoping someone would ask that question, thanks.

[AllAmericanFiveRadio]

Putting an antenna on the collector may work if you add an RF choke to keep the RF energy on the antenna and out of the batteries. Also using a different oscillator may work better. What is great about this little project is it does not cost a lot of money to do some experimenting. This circuit is just one idea.

Rick

[mig189189189]

Awesome video!

I'm going to try that project one of these days!

[AllAmericanFiveRadio]

Thanks. It is a fun project and can be useful.

[jefferyb304]

Really cool !!! When you tapped on the coil it reminded me of the video organgrinder010 made tapping on the reverb springs.

[AllAmericanFiveRadio]

Thanks. Yep it sure does sound like a reverb.

[joernone]

Cool, Rick, cool. How far will something like that transmit?

I still plan on building the McWhorter AM transmitter. Things just keep getting in the way. I've got the schematic and the parts list stapled together. Trust me, I will get it built. I need that baby.

Regards,

John

[AllAmericanFiveRadio]

Hey John,

This one not too far. But if you get out the books or do web searches on making High Q oscillators you could get it to cover the house on FM. This transmitter is very easy to build and it works. The idea is to get people interested in experimenting with it.

Regards,

Rick

[coolbluelights]

wow that's an old battery! haven't seen them with testers built in in years! I built a very small FM transmitter a few years ago but I had a lot of stability issues. I had a ferrite slug in the coil and it kept moving out of place

[AllAmericanFiveRadio]

I keep a supply of batteries in my refrigerator. It does keep them good for a longtime. Yep, transmitters are finicky. This one would also have a problem with temperature. In the house not so bad, but outside it would drift a lot as the temperature changed.

[mancub0]

Interesting part about tapping the coil at the end of the video.

So if you mounted the coil in such way that one end is glued to let's say a stretched membrane of sort (skin) and the other end to a fixed board you could potentially create a microphone as well without the need for an audio input?

[AllAmericanFiveRadio]

Yes if it varied the shape of the coil in proportion to the sound, it would act as a microphone. But I am sure the sensitivity would be lower than a conventional microphone. I just finished listening to the FM transmitter, old radio programs. I had it on for over four hours. Had to adjust it twice as the battery voltage lowered a little, but it was still going strong. Thanks.

[HD7100]

I built a Ramsey FM stereo transmitter kit that I use to stream Live365 throughout my house. It works good but the power supply they sent makes it hum and the fact it isn't mounted in a metal box causes it to have some RF feedback into the audio. I powered it with my computer power but noise from the computer feeds into it. I fixed the RF feedback by clipping test leads to the audio grounds and leaving them hang over the edge. If I mount it in a metal box and use a good supply that should work.

[AllAmericanFiveRadio]

Good. I built the Ramsey FM stereo transmitter kit also, and it is excellent quality. It surprised me how well it works. I have it on the kitchen counter with a very small antenna and I have been able to pick it up over two blocks away. Very nice transmitter.

[MrTwiffler]

wow this helped a lot with something i was trying to experiment with

[AllAmericanFiveRadio]

Thanks. I hope it helps.

[Vinylrecordsneverdie]

Not only you made a homemade AM/FM transmitter, but also pickup head.

[AllAmericanFiveRadio]

Yes, if you attached a needle to the coil or close to the coil, it would play on FM. Thanks.

[ms2333]

This is awesome. Your videos always blow my mind. I wonder if you would consider doing a second video and explain in detail why all the components are in the circuit, and why they're connected as they are.

[AllAmericanFiveRadio]

This circuit is not very efficient but that should make it easier to build, I hope. I would like to show some modifications to this little circuit and when I do I will be glad to go through each component. Of course you dont have to wait, just email me you questions and I will try and answer them. Thanks.

[umajunkcollector]

I've had a few people ask me about doing this for their OLD AM radios, I guess they want to play some OTR tapes into the radio. When I was a kid, I think their was a Radio Shack Knight kit to make a radio transmitter, I had one and pretended to broadcast over the radio. I also used to do this with an old walkie talkie. Some people do this over the CB, but that's illegal. Some cheapo wireless mics used FM broadcast band too. Fun stuff.

[AllAmericanFiveRadio]

Yes it is. I hope this very simple circuit will work for everyone interested in doing a little experimenting. I may one of this several years ago. You could tune it to AM or FM, it would bock out channel 5 TV and it also brought up the Clayton 2meter repeater, woops. Thanks.