DIY AM Transmitter

Everybody knows about AM radio. And one of the most popular electronics projects of all time is the AM receiver. But what about an AM transmitter?...
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[@coolbluelights]

This gives me flashbacks to electronics courses I took at ITT tech years ago. Lots of formulas and theory that isn't really compatible with the way I learn.

[@peterking2794]

I built an AM transmitter using tubes. I works quite well, but prone to drifting off tune when I move my hand near it. I must get around to building a better one one day (with tubes.)

[@Dazzwidd]

play with the value of R4 so more signal is coupled to the output stage. use a molded inductor in your oscillator. Swap out R7 with an inductor... use a loopstick aerial from an AM radio. Connect the anrenna wire (which may not be needed anymore) to Q2 collector. Dispense with R9. reduce R8 to 100 ohms in series with 22 ohms, the latter connecting to Q2 emitter. In the middle of these 2 resistors, connect a 10nf capacitor to ground. These are just immediately obvious improvements at a glance. There's more I see that I would try

[@qwertykeyboard5901]

I have this Sears "automatic" germanium transistor radio. Three IF stages, good size speaker, it sounds pretty good! Oh, and it's sensitive! AM radio can sound pretty good.

[@DavidALovingMPF102]

great job. You have some nice electronics there. I made an AM transmitter using a 500 khz resonator. Its harmonic hits 1.37 mhz. Sounds good, no hum, good range. Audio input from headphone jack of boom box cd player. Video here on youtube.

[@xzddakfdmiug5832]

I like the look of that old radio. I wonder when stores stopped selling that type of battery.

[@thurlravenscroft2572]

Looks like an A21PX battery to me. Available on Amazon.

[@MakeDoAndMend1]

Many thanks for this video. I am currently building an am transmitter. All going well so far. Cheers from George. Ps now it's the matching transformer etc. Vizio on my channel. 😊

[@matthewvillena8635]

Tried the circuit and the oscillator and modulator works. What voltages did you use for the OP-AMP supply?

[@PasseScience]

Hi could you explain the 9:24 top right (what's neither the oscillator nor the modulation), 9:34 so it's not really Amplitude Modulation but some kind of DC additive translation? (I am interested in electronic and the topic in general for only 4h, be gentle :) )

[@ohger1]

Regarding the 4V mercury battery... Early American RCA pocket transistor radios from the early 60s used these batteries, and they are of course unavailable. I bought a tiny RCA turquoise radio in mint condition off Ebay and built a rechargeable pack from 1/3 AA nimh batteries and rewired the headphone jack into a charging jack. I just ran in a 5V wall into the jack using a resistor and zener inside to limit current to maximum charging rate assuming full discharge. This makes for a very slow charging system (maybe 8 - 10 hours for a full charge) but the pack would run at least two weeks on one charge when he brought the radio to the beach to listen to baseball games (that RCA was very sensitive and did better than the Sony he was using). Food for thought for those wonderful and beautifully built American made transistor radios.

[@Martock1017]

The presence of an output transformer to the speaker suggests that this set uses germanium transistors. It looks as if there is another smaller audio transformer inside which drives the push-pull audio output stage. With the arrival of silicon transistors it was possible to eliminate these components by using different circuit configurations. Although these transformers have not been needed for nearly 50 years, components, such as the Eagle products LT44 & LT700 transformer pairs are still advertised by component dealers.

[@ohger1]

@@Martock1017 My experience with these (my family was in the TV radio repair biz) is that these were very reliable radios. Once in a while we'd see a transistor croak and of course now that they're 60 years old the two or three electrolytic caps are shot, but overall, I can't recall seeing an open xfr in any of them, but that's good to know.

[@gregjones3660]

Can you send a parallelogram with your amsmitter?

[@_xelua_]

how do you manage to transmit it, i mean the antenna? for 1Mhz?

[@overengineeredinoz7683]

Nice video

[@SineLab]

Thanks

[@gameyord7182]

make a large coil in a iron tube, put another coil on top of the first coil, connect the second coil trougth the positive rail of the output transistor, connect the bottom of the first coil to one of the cables of the second, tada, now you have a compact antenna that´s a few feet long....

[@danielraducu9073]

one question, you added a 22kresistor at the end, i do not understand where? is it that r15 resistor from 9:24 minute ? please explain more, i really want to try this circuit...

[@SineLab]

Yes, I meant R15. :)

[@danielraducu9073]

@@SineLab thank you !

[@paulperano9236]

I have the same power supply, but don't use it for low signal projects - too much switch mode noise. I just use some AA Batteries instead - no noise.

[@SineLab]

Yes, it's a really big problem with that power supply.

[@SpeccyMan]

I use a good old school linear bench PSU.

[@cmuller1441]

Hello. I think your power supply may be a switching one that produces a lot of high frequency ripple. That's not a good thing for AM.

[@SineLab]

Yes, that's why I used a battery :)

[@GregCoonrod]

Time to get your Ham Radio license!

[@teresashinkansen9402]

I was expecting it would need something like 40 D size batteries to work for 20 minutes.

[@bsuryasaradhi6816]

Why do you have a 50 ohm termination, your emitter follower has an input impedance of 5k ohms, but you are supplying a 100k ohm input

[@bsuryasaradhi6816]

When the output rf signal goes below 0 volts the emitter follower wont work, as the capacitor will turn off the emitter base junction, You need an AB emitter folllower for this, i dont understand why the caps are 1uf either

[@electroimpyo]

❤

[@manuelvillanueva3753]

Lots of "anyways", thanks a lot!😂

[@englishrupe01]

"Pocket radio"? Who the heck has pockets that big? Elon Musk? Good video, thanks.

[@1bunnybuster]

I can get 40 watts AM out of my yaesu ham radio with a long wire antenna.

[@mellonhead9568]

i made a 9v battery powered FM transmitter myself..... 5-10m...... next i wanna do TV ransmitter

[@GiuseppeGibilmanno]

this is AM

[@PinkeySuavo]

i wish i was smart

[@SpeccyMan]

If you were smart you'd know it is were and not was. 😉

[@PinkeySuavo]

@@SpeccyMan exactly, that's what I'm saying

[@Stefan0719]

No offense... but... the audio quality is very poor. ... Watching the video, you are smarter than I am, calculating all that stuff, but it also shows me that you are a lot into theory and not pracitcal thinkering. Seing how extremly low impendance you made the colpitts oscillator, you could modulate the oscillator alone, and get a good AM signal. Based on the low value in the oscillator (2,2k Emitter) the oscillator itself (the coil) will probably transmitt more into the radio than your actual antenna, since the radio does receive an "inductive" signal (magnetic field) rather than "capacitive" what your (non matched) antenna is tansmitting. Some values "underline" you´re a lot into theory... like the 1µF (!) capacitor between the oscillator and the buffer, but then added a 100k resistor in series... Also, why do you use a Collector circuit as modulator, and then use an op amp to compensate for it´s lack of "audio gain"? At this low power level you could hook up the "rf amp" directly to the output of the LM358. Why does Q1 not have a RF blocking capacitor (from Emitter to ground)... the RF flows into the transistor, causing issues (distorted audio could be one of the issues). If you want, I can re design the circuit for you so that the audio actually sounds loud and clear (I´m reffering to the first two audio samples you made, with vocie very audible distorted)... *checks the schematic* Am I seing that right, that there is no Capacitor between + / - ... like .1 µF (104) to block the RF? ... like I said, you are smarter than I (math) but you lack practical experience... sorry... I hope this doesn´t read offensive, I was just "astonished" how poor the audio quality is for such a big (lots of efford) circuit... Simpliest way to solve it: Remove the 1µF / 100k and replace it with 10nF (103) and 1k. Remove the LM358, remove the R6... and connect R5 to the collector of Q2 (it also might work with R5 still to B+) change R7 with R8 (1k from collector to B+ and the 100R in the emitter) Add a 10nF ... 100nF (whatever you have) ceramic disc capacitor from the emitter of Q2 to ground. Then remove Q3 and replace it with another 2N3904. To the collector of this 2N3904 now goes the 100R resistor ... it´s emitter goes to ground, and between collector and Base add a resistor something like 220k ... 470k ... now feed in audio on base of that transistor via a 1k 1µF something like that ... this will give you a well working transmitter... have not tried it thou, but your oscillator is having such a low impendance (4,7nF is a lot usually you have like 470pF but therefore the inductor has a few hundret µH, not 10µH) ... it should work.

[@micahtritscher951]

Hi, is there any chance you could draw up the circuit you suggest so I can better understand what you are describing? Cheers.

[@gregjones3660]

transmister

[@h7opolo]

i really didn't like your fraud