AM transmitter based on the LM386

[@1pcfred]

John's pirate radio is on the air with everyone's favorite bossa nova song.

[@generessler6282]

Man this brings back memories. As a 12-year-old In the late 60's used to fiddle with AM like this. Owned just one transistor that would work at one megahertz. All circuits had big warnings about max antenna length 10 feet. Used to wonder if I went longer whether an FCC van would show up in the driveway. Still remember that 100 turns of #28 mag wire on a 1 inch air core and a 365pf variable cap would tune the broadcast band. Great stuff. Thank you.

[@acestudioscouk-Ace-G0ACE]

I loved this, great boyhood story!

[@wood1y]

Thanks John. Great video, as usual.

[@iblesbosuok]

I built circuit like this about 30 years ago. uA741, BD139, 2N3053 sweet memory.

[@migalito1955]

I used a 555 for an AM transmitter over a year ago for giggles. I vaguely remember using filters to change from square wave pulses to more sine like. I also remember it liked to splatter all over the AM dial.

[@oldblokeh]

For the triggering, use trigger holdoff. This allows you to set a delay after the first trigger during which it will not retrigger.

[@isoguy.]

Your vids are amazing, so many skills. Saw one of your vids where you showed your drawing skills, all I can say is watch out Bob Ross drawing schools. Ever thought of launching a drawing channel? Life for most people is a $@% €#, sure some have big houses, boats, fast cars but generally that's a cover for their pain and inadequacies, learn to enjoy what you have, this leads to contentment, believe me I learnt the hardest way possible. A person is admired and remembered for what they pass on to the next generation, not for the car's, boats, houses and other material things they accumulate during their lifetime. Your ability to design, present and upload successful vids is something I can only wish to aspire to. Thus far your vids have been an inspiration to me, so thank you for sharing your wealth of skills.

[@woodcoast5026]

The capacitor on the single rail op amp output is not just to block the DC. When a class B amplifier circuit powering a speaker, is single rail power supply, a capacitor is required to provide a current path for the negative voltage swing.

[@TrystansWorkbench]

Good work John, as always. I would never have imagined the LM386 in this use before. Get a Ham licence then you can explore this much further. :) Great stuff.

[@joohop]

Nice Work John Bless Up Fella

[@researchandbuild1751]

I use a circuit sonwhat like this for my low power AM station. The LM386 provides power to a class C transistor switch which then is filtered. I use an Si5351 to generate the drive signal on the transistor so i get perfect frequency accuracy. The Lm386 essentially modulates the power going into the class C a amplifier, this technique is called high level AM modulation My station has an arduino MP3 player with 10 hours of Art Bell radio programs and it switches tracks randomly. Its been running for almost 2 years now and has a range of about 2 miles. It is connected to a 10 foot copper pipe with a wire capacitive hat, and a metal mesh on the ground as counterpoise. The antenna is tuned with a large coil wound on a 3 inch diameter PVC pipe, using a NanoVNA to get the best tuning. Impedance is only around 15 ohms or so with such a short monopole antenna though so of course its pretty inefficient but i have picked up my station with my car up to 3 miles at certain locations, i beleive i am putting out about close to 100mW at the output of the antennna amp bit this wont translate much to RF with a short antenna like i have so RF is probably 1mW

[@acestudioscouk-Ace-G0ACE]

I checked your channel listing in the hopes you had done a video about it. Would love site of a schematic!

[@SpeccyMan]

@@acestudioscouk-Ace-G0ACE Sight of a schematic would be far better. 😉

[@tonypike8774]

Thanks John. Another interesting video mate and the first I've watched on transmitters. I'll be watching more now.

[@TheDradge]

I have 2 ginger tom assistants. They are great for rummaging in the depths of miscellaneous electronic workbench junk. Great video John!

[@sadunnakipoglu9471]

Thank you so much for this video.

[@andymouse]

Amazing little circuit, very well explained ! I built something like this when I was a kid, just copied from a book so didn't realy understand back then, but it fuelled my love of electronics and I see this and it's still great fun, something fun to play with on a rainy (I'm in the UK) Sunday...a little off topic but I have started playing with the Texas instruments circuit simulator called ' TINA' have you heard of it ? I have put in the JAT501 and have small signal in big signal out, thats about as far as I've got ! so now time to go back through your tutorials and see if I can replicate your design adjustments as you developed each part. I don't have the correct output trany's so put put a TIP30 and 31 in there, so off to do my homework as the sim has asymmetrical clipping, the positive half is clipping first...would love to see your transmitter refined a bit...cheers.

[@JohnAudioTech]

I've heard of TINA but never tried it. Have fun with the tinkering.

[@TheTrueVoiceOfReason]

Vegematic1966 rises from the past. Always good to revisit an oldie but goodie. I only vaguely remember that transmitter. Speaking of oldies, whatever happened to that plexiglass subwoofer? And those TL speakers you built? Ah, fun days...

[@JohnAudioTech]

I still have the plexi sub. The TLs are long gone.

[@martinda7446]

Good glad you grown some balls. I blame it on the parents. 😸 Give Snickers a rub from me.

[@theschnilser7962]

That's some interesting stuff to tinker with. About 2 years ago I tried to build two super low power AM transmitters, out of just two transistors each, one for operation with a quartz crystal, the other one based on a LC resonator. I might have gotten away with just one transistor each, using the audio source as a modulator, but a little integrated amplifier couldn't hurt, right? The experiment was a success, despite of the LC circuit being a little unstable. The audio quality was surprisingly good, but being a very low power circuit, the signal was not very strong.

[@odindimartino597]

A good way to trigger on a modulated AM simply to trigger to the modulated signal from another input or the "ext trigger" input

[@JohnAudioTech]

Yes that makes sense. Trigger off the test tone on channel 2. I wasn't sure if there was a more direct way of triggering.

[@ferrumignis]

To get solid triggering use another channel and use it to trigger direct from the LM386 output rather than the modulated signal. Using transformer coupling between the LM386 and the RF power stage collector would yield a significant increase in RF output.

[@SuburbanDon]

Jeeeez I've spent a lot of,time trying to make a transmitter and never got a waveform anywhere near this good.

[@killcar5nbike2]

Several comments already on ways to sync trigger. I know my cheap Chinese scope has LPF/HPF filters on the trigger menu I use. I'd imagine that one would have it somewhere.

[@markg1051]

Re the triggering, if your scope has EXTERNAL Trigger input, feed your audio signal into it and set trigger source to external. This will end up with a rock stable AM waveform.

[@JernD]

Great video!

[@noelj62]

Interesting idea

[@acestudioscouk-Ace-G0ACE]

Great video! An approach I haven't seen before. I learned a lot. As a radio ham, I'm now wondering if I use the circuit as a basis for a QRP (low power) transmitter.

[@iwbnwif]

Great video and circuit. Would be nice to pair with a TA7642 to make a little walkie talkie.

[@jrausa1]

Hi John- One more question if I may. What voltage levels does the square wave source alternate between? Does the transistor alternate between cutoff and saturation? Thanks again. -John

[@EngineeringEssentials]

I am going to try this 😍. If I do not monitor output using oscilloscope will the wining noise go away?

[@trevorvanbremen4718]

The 'whining noise' may well shift to come from the guy in the radio detector van outside!

[@SuburbanDon]

You gotta like anything with balls.

[@jrausa1]

Great video! I’m going to build it. One question- Instead of connecting ground to a copper pipe, is it okay to connect it to the third prong of my wall outlet, or the green terminal on my power supply? Thanks.

[@JohnAudioTech]

Any good earth ground would be fine.

[@McTroyd]

Based on this, it seems like one could make an FM transmitter with a 555. Use the output of the LM386 to drive the trigger/threshold pins. Output an intermediate frequency directly from the 555 (455 kHz? 1.6 MHz?), and mix it in with the higher frequency oscillator. Am I completely off my rocker?

[@theschnilser7962]

That might be something to try in the future! I do understand the concept of mixing the frequencies, but how can such a circuit convert the signal from AM to FM?

[@McTroyd]

@@theschnilser7962 AM is "Amplitude Modulation," as John shows here. FM is "frequency modulation," where the amplitude stays the same, but the frequency shifts slightly corresponding to audio. The threshold/trigger pins on a 555 are what determines the frequency the 555 switches at; I was wondering if the output of the LM386 could be used for that. The 555 would need to be at a standard intermediate frequency (abbreviated IF; I forget what terrestrial radio uses, but I think it's 1.6 MHz). Use a ~100 MHz oscillator to mix with the IF and perhaps it's receivable? Mixers can be diodes or transformers -- there's schematics all over the Internet.

[@theschnilser7962]

@@McTroyd What an interesting approach on frequency modulation. I might try something like that next weekend, since I should have all necessary components on hand. As you can see in every generic 555 oscillator circuit online, pin 5 or trigger is connected directly to the RC network, which is setting the frequency and duty cycle. I am confident, that the output of the LM 386 can be used to shift the frequency of the 555 a fair amount. Since there should be a difference in voltage between these pins, I would recommend adding a resistor. Maybe another resistor to ground and coupling through a cap might improve the quality, since the lower frequencies usually have a bigger effect the modulation. But the last thing is mostly speculation, since I do not know if that applies to the 555.

[@zlac]

My gut feeling is that it would change frequency way too much and make the whole thing not very stable. Standard FM radio has just 10MHz badwidth and a lot of newer ones are 5Mhz.

[@McTroyd]

@@theschnilser7962 If you remember to do so, I'd be curious how that turns out. Only very recently has RF exited the "black magic" zone for me, and I'm still getting my feet wet. From what little I know, I'd wonder most whether harmonics or self-oscillation would be better or worse in such a setup (especially since the 555 switches a square wave).

[@jstro-hobbytech]

That's what too cool

[@girishss5118]

Can you please make a video on.Bob Cordell bc-1 amplifier..?

[@MrTauron77]

Megépítettem ezt a kapcsolási rajzot amihez a vivőhullámot egy 555-ös IC adta, de a BC337 tranzisztor nem vált be, mert torzított, ezért egy régi BFJ17 tranzisztort használtam fel hozzá. A vivőhullám és a tranzisztor közé csak egyetlen potmétert kötöttem be, ami elég is volt. Felmerült bennem az a kérdés, hogy TDA 2003-as IC-vel is meglehet e ezt építeni?

[@jstro-hobbytech]

John. Please do a "components I keep on hand video". None of my cheap ebay or Chinese kit stuff well at all. It's very disheartening. I'm doing the star ground properly (I believe) and shielding all my wires.

[@butsukete1806]

So I can use this as a Eurorack VCA without needing a patch cable?

[@christopherkise]

cool

[@KissAnalog]

Fun circuit! Nice video John!!

[@MrTauron77]

Nos eltelt két év, és azóta egy Pixie2 oscillátorral cseréltem le az 555-ös IC-t ami be vált, de nem teljesen.

[@AliensInc.]

I was wondering, the square wave you use into the transistor, as it is square, will that be like the sampling rate of the audio that is added to the sine wave? You use 1MHz for the square wave but that could really be anything, am I right or way off?

[@ubergeeknz]

Not quite. It defines the carrier frequency i.e. where on the AM dial the signal will be. So it has to be somewhere in the frequency range of your receiver. And within the capabilities of the other components in the circuit.

[@AliensInc.]

OK, but it's square wave, so how can that sound great in the receiver as it not sine?

[@ubergeeknz]

@@AliensInc. it gets transformed into a sine wave as it's fed into the resonant circuit

[@ubergeeknz]

@@AliensInc. and the carrier wave gets "removed" by the reciever, what you hear is the original signal or the "modulated" signal

[@dare-er7sw]

Modulation percentage??? 50% ?

[@nsfeliz7825]

i like arduino. but it seems everyone these days think arduino is electronics. theyre missing out on the fun of analog stuff. amplifiers oscilators etc.

[@KissAnalog]

To get the trigger, you could try using the trigger delay so that it ignores the high freq and looks for what you set the delay to. Maybe worht a try;)