Hi all,

I'm looking for information on an apparatus that I've seen advertised that can produce an AM signal from a digital source.

This subject has probably already been discussed so perhaps someone could either direct me to the content or just throw some light on the subject.

Cheers
Pat

Yes, we have discussed various low power AM transmitters and kits, however the site's search function isn't finding those threads/posts for me at the moment. Maybe Brad can find them.

I just searched for "AM transmitter"

https://vintage-radio.com.au/default.asp?f=1&th=1163
https://vintage-radio.com.au/default.asp?f=1&th=750
https://vintage-radio.com.au/default.asp?f=1&th=429
https://vintage-radio.com.au/default.asp?f=1&th=338

Some of these threads are quite old. This is just four picked at random but there could be others available.

I just searched for "AM transmitter"

So did I and got zero matches.

Hello Pat .
I think you are referring to an AM transmitter that allows you to feed any audio source into its audio input and it transmits an AM modulated signal somewhere around 700kHz to tune your radio in to. If you have a phone or a tablet you can find a digital radio app which you can plug into the devices input. I have built 3 different types non are my design. The first was a valve unit put out by an article ini a supplement from Electronics Australia . The second was a solid state unit put out by silicon chip magazine. The third was in Kit form from HRSA if you are a member of HRSA you can buy this kit still. And lastly and this is the reason I am answering you is there is one currently on sale on EBay I bought one to see what it was like to compare the one I received I would NOT !, recommend you buy here are my reasons for this. It is supposed to be able to work from a 9 volt battery . Part of the circuit has an op amp which gets its supply via another IC it requires at least 5volts on the op amp the internal circuitry only ends up delivering a lilltle over 4 volts to the IC so it may or may not work and if the battery gets even a little bit low it will not work at all. The unit is all surface mount stuff and there is no available adjustment for the AM signal to be adjusted up or down from its preset value around 700kHz.
Ok you are supposed to be able to run this off a 12 volt regulated switch mode plug pack in so doing so, the output frequency falls lower right onto another station close to the ABC and cross modulation distortion occurs and as I have already stated you cannot adjust the operating frequency back up unless you start changing surface mount components.
This is what I experienced with the unit I bought, maybe mine was a dud.So on what I experienced with the one I bought I would not recommend it. I had some dialogue with the guy and his suggestion was do some surface mount capacitor changing which I can no longer do and you need a very expensive rework station to do that type of work anyway.
The 3 I have built all have the ability to adjust the opeating frequency to a quite spot on the band.
If you are able to construct stuff and are a member of the H.R.S.A. buy their kit it works well and is not very expensive.
Regards Jim

The last thing I made to transmit used a quad NAND gate as the oscillator but was crystal locked & fed into a line that turned it into a modified sine wave & the modulator was a dual gate FET.

Marc

Thanks everyone for their response I will check it out!! Yes Jim you were right on the ball, I was thinking of buying the one on ebay so thanks for that advice!

Cheers
Pat