AM transmitter circuit questions

[anonxa]

Greetings.

I am trying to self-teach myself in electronics until I can get some formal education in the field (currently working on finishing my computer networking degree). I am very interested (right now) in AM band broadcasting. I found the directions for making a small AM transmitter, which ended up like the attached PNG.
Since I completed this I have craved more, as I have found 2 limitations that are starting to bother me. The first is that the transmitter is stuck at 1MHz. I have found a little info on oscillators that I can change while the circuit is in operation, but nothing that I can make myself. Through some reading I found out that an oscillator can be made from just an inductor and a variable capacitor. I have two questions on this, am I correct in this, and how do I make these out of more common items (cardboard, wire, foil, solder, etc)?
The second limitation I think I already know how to address but I guess am not brave enough. The circuit isn't putting out enough range as I would like (about half). What is the easiest way to increase the range (I'm hoping for maybe a few added components)?

 

[Hero999]

Another problem is that the oscillator is probably squarewave and therefore gives just as much power in harmonics which will interfere with other stations.

Why not go with FM which is much better quality?

 

[stevez]

You might consider amateur radio as a way in to that area. While other modes have made AM less popular (some might say obsolete) it is a mode that is still used today. A license is required to use the equipment. Amateur radio publications do provide detail on theory and practice. ARRL Radio Amateur's Handbooks from the 1960s have quite a bit of info - all valid today though more current publications incorporate the advances in technology. Quite a few of the active AM folks use old broadcast transmitters.

I mention amateur radio for another reason - the publications are written for a very broad audience that include the many people who do not have backgrounds in electronics. While not a substitute for a formal education the material is often sufficient for self-teaching.

Best of luck.

 

[anonxa]

Why not go with FM which is much better quality?

Well I want to do that but first I want to learn about AM and the basic components. My aim really was to find out how to make an oscillator that I could change the frequency of (either by a dial like a potentiometer, variable oscillator that I could make myself with cardboard and foil, or by some other means).

You might consider amateur radio

I want to do that kind of thing, to keep my mind active in this kind of thing while my education wanders away from it.

A license is required to use the equipment.

I plan to do this very soon so don't worry about any issues like that.

 

[stevez]

A Variable Frequency Oscillator or VFO is what a radio amateur would construct as a way of providing an adjustable but relatively clean and stable source of RF within a narrow range of frequency. Lots of info in amateur radio literature about VFOs.

 

[anonxa]

A Variable Frequency Oscillator or VFO is what a radio amateur would construct as a way of providing an adjustable but relatively clean and stable source of RF within a narrow range of frequency. Lots of info in amateur radio literature about VFOs.

So this is something to google and is constructable on one's own?

 

[blueroomelectronics]

Just what range are you hoping for? 1m, 10m, 1km?

 

[anonxa]

Something like 55kHz to 5MHz (enough to play with)

 

[blueroomelectronics]

Range as in distance in Feet or Meters.

 

[RadioRon]

The range of frequencies that you mention is too ambitious for your first time. You should aim to make an oscillator for 1.1MHz to 1.3 MHz or similar smaller range. Here is a link that you can use to learn the theory. The design examples are for frequencies that are a bit higher, but you may learn enough to find that lowering frequency one or two octaves (by half or by quarter) usually involves increasing the inductance and capacitance values of the oscillator tank circuit. So you can use the circuits in this link, but you may have to increase the inductor and tank capacitor values.

**broken link removed**