Recently I repaired a tube radio for a family memeber. unfortunately there aren't that much radio stations any more on the MW bands and the tube radio doesn't have UKW/FM
So it would be nice to have a small modulator/transmitter that could transmit to the radio. I have some bluetooth audio modules so if I use this as music source it would be neath and easy to stream music from smartphone etc.... to the tube radio.
So does some of you guys have an idea for a good and stable AM modulator/transmitter. Most schematic on the net are very simplistic and I want a good modulation and a clean signal without interferencing with something.....
So an oscillator of around 1Mhz and an Am modulator. I was thinking of using the AD633 https://www.analog.com/media/en/technical-documentation/data-sheets/AD633.pdf page 10 shows an example Am modulator. now a clean and stable 1Mhz oscillator...... An extra idea would be to add extra bluetooth functions like changing the frequency but maybe that's asking to much.
As we are talking about mw's a small output transistor could be nice but maybe not needed.
So it would be nice to have a small modulator/transmitter that could transmit to the radio. I have some bluetooth audio modules so if I use this as music source it would be neath and easy to stream music from smartphone etc.... to the tube radio.
So does some of you guys have an idea for a good and stable AM modulator/transmitter. Most schematic on the net are very simplistic and I want a good modulation and a clean signal without interferencing with something.....
So an oscillator of around 1Mhz and an Am modulator. I was thinking of using the AD633 https://www.analog.com/media/en/technical-documentation/data-sheets/AD633.pdf page 10 shows an example Am modulator. now a clean and stable 1Mhz oscillator...... An extra idea would be to add extra bluetooth functions like changing the frequency but maybe that's asking to much.
As we are talking about mw's a small output transistor could be nice but maybe not needed.
The XR2206 sine wave generator will do AM; see page 12 of the data sheet. It is capable of 1MHz operation as well and can be phased locked to xtal reference.
Many older linear circuits are not-so-linear at 1MHz.
Call me old fashioned. I still like tank circuits and high-level modulation.
Look at this, "Micro Power AM Broadcast Transmitter" about 1/3rd down the page. The CMOS makes a reliable and easy 1MHz oscillator. Lower jellybean NPN is a class C radio amplifier, DC-fed by a choke. C-L-C pi-tank trims the overtones. Upper jellybean NPN takes high-level audio and modulates the class C amplifier. This trick works really excellent to 95% modulation. (It is not efficient, and went out of fashion 50++ years back in KiloWatt work, but for across-the-room we can afford the inefficiency.)
If the specified lamp is no longer available, use a 20-40 Ohm resistor.
The audio input is 500 Ohms and needs 3V peak for full modulation. An ipod won't do 3V peak. Put an opamp (hi-fi preamp) in front.
As the article says, it is impractical to "match" 1MHz to a couple feet of wire, and you are not likely to build a 1,000 foot tower to get a great match. But milliwatts even microwatts will get across a room fine, unless some nearby transmitter is on the same channel.
Call me old fashioned. I still like tank circuits and high-level modulation.
Look at this, "Micro Power AM Broadcast Transmitter" about 1/3rd down the page. The CMOS makes a reliable and easy 1MHz oscillator. Lower jellybean NPN is a class C radio amplifier, DC-fed by a choke. C-L-C pi-tank trims the overtones. Upper jellybean NPN takes high-level audio and modulates the class C amplifier. This trick works really excellent to 95% modulation. (It is not efficient, and went out of fashion 50++ years back in KiloWatt work, but for across-the-room we can afford the inefficiency.)
If the specified lamp is no longer available, use a 20-40 Ohm resistor.
The audio input is 500 Ohms and needs 3V peak for full modulation. An ipod won't do 3V peak. Put an opamp (hi-fi preamp) in front.
As the article says, it is impractical to "match" 1MHz to a couple feet of wire, and you are not likely to build a 1,000 foot tower to get a great match. But milliwatts even microwatts will get across a room fine, unless some nearby transmitter is on the same channel.
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the last circuit looks very nice and simple. Xtal makes it stable and modulation should be without to much distortion and the audio is not frequency limited. (some of those tube radio receivers offer relatively wideband audio on MW bands...)
I think I am gonna try that circuit. adding an audio buffer could simply be an opamp or to stay al discrete maybe a simpel emittor follower could work...
I think I am gonna try that circuit. adding an audio buffer could simply be an opamp or to stay al discrete maybe a simpel emittor follower could work...
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