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Is it possible to build an AM radio transmitter with only discreet components? Answered

I don't need to have it have good quality. I'll only be sending morse code, so I don't need any type of audio clarity. If it's possible with discreet components, can you provide a schematic? If not, could I use a 555-based circuit? Again, schematic please. Thank you!

(For anyone who doesn't know, discreet components means no IC's , otherwise known as "chips".)

EDIT: I'd also like to not use a crystal osscilator. Thanks!

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rickharris (author)2012-04-22

Yes of course they were doing this long before ICs were invented

https://www.google.co.uk/search?tbm=isch&hl=en&source=hp&biw=1920&bih=918&q=AM+radio+transmitter&gbv=2&oq=AM+radio+transmitter&aq=f&aqi=g3g-S7&aql=1&gs_nf=1&gs_l=img.3..0l3j0i24l7.2112.11807.0.11928.20.20.0.0.0.0.180.2138.8j12.20.0.egsbsh.1.hLi3YUhFo2I


A number of circuits here

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user

I'd like to be able to choose my own frequency to transmit at, rather than being restricted to a crystal osscilator. Most of these use a crystal osscilator.

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user

In most/all countries there are national and international laws covering the transmission of radio signal, the frequency bands you can use and to some degree what you can send over it.

They also require that you have tight control over your transmitted frequency and the band width you use hence the crystal control.

This doesn't mean your limited to a single frequency though. The crystal provides an accurate reference frequency. Look up HAM radio to check out the relevant laws.

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user

Do you mean to say I can alter the frequency a crystal puts out? How?

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user

The crystal produces a reference frequency. For example if you divide this frequency in half - then you get half that reference frequency.

You don't tell us why you need to transmit or what your experience is so it's hard to decide where you need to be looking.

In the Ham radio world in general you transmit on a single frequency but scan your receiver across the waveband to pick out your desired signal.

If you think about it if your transmitting on the same frequency as others your messages are going to get mixed up and garbled.

It's not essential that you use a crystal BUT it is essential that you obey the laws governing the use of radio systems. Although these have become relaxed over the years the air waves are still policed and if you interfere with commercial transmissions you may/will find some official knocking on your door. If your transmitting your easy to find!

It seems to me that you need to do some basic research into radio techniques so you can understand the principles.

Here is a starting point. This is the page for the radio society for Great Britain. This is  the international organization that regulates the air waves

Some theory principles

Radio principles

radio wave propagation

Navy training PDF


Some build it sites

here
here
here


happy researching! :-)  I got into elect6ronics because my Chemistry teacher was a radio ham.

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user

Oh. Well I'm making this to have a wireless link between my TI-84 calculators. I was planning to use infrared, but then I found out there are two data lines, and IR would blend into each other. So I figured I could convert the data into radio for one of the signal lines and IR for the other. IR is easy. But I haven't done anything with radio yet.

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user

I would look at ZIGBEE

http://en.wikipedia.org/wiki/ZigBee

or xbee

http://www.picaxe.com/Hardware/Project-Kits/XBee-Connect-Starter-Kit/


http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Products/AXE213

might work for you

http://www.picaxe.com/Hardware/Add-on-Modules/433MHz-Radio-Transmitter-and-Receiver-Pair/

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user

Again. I'd like to avoid having any complex boards to do the work. There must be some way to do it!

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user

If I were to do this over a short distance I would use:

1. Wire
2. Optical fiber
3. IR
4. Wireless but buy a commercial system
5. maybe it can be done on a DIY basis if your prepared to experiment, have the right test equipment and understanding of radio principles.

Data transmission would probably be best coded/decoded with a micro processor that way you can use DTMF or Morse code, or even plain old binary using say ASCII - in any sort of serious system you will need some kind of error checking or your data will be subject to doubt,

I wish you good luck but My experience as a former Radar engineer is that, even knowing the principles, radio systems are really difficult to get working.

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user
iceng (author)rickharris2012-04-24

Very neat discussion good pointers +1

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Kiteman (author)2012-04-22

Entirely possible. Check here: http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html

(There are a couple of other simple options there.)

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4lifenerdfighter (author)Kiteman2012-04-23

I'd like to avoid using a crystal osscilator.

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user
Kiteman (author)4lifenerdfighter2012-04-23

If you just want to send morse code, why not build a spark gap generator? They broadcast on almost every frequency at once...

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user
4lifenerdfighter (author)Kiteman2012-04-23

Aren't those illegal because of some sort of bad interference?

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user
Kiteman (author)4lifenerdfighter2012-04-23

Quite possibly, but so is any other unlicensed transmitter with a range over a few feet.

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iceng (author)2012-04-22

ICs are only an assembly of many discrete transistors, but you know that.

A little as several months after the introduction of the IC Norton said
" Wow we can make an AM !! " , followed by the FM, SSB, spread spectrum
and the radio was born :-)

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user
4lifenerdfighter (author)iceng2012-04-23

Well, yes. But I'd like to avoid any IC's other than 555. Whether I build them myself or buy them doesn't matter.

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Re-design (author)2012-04-22

What do you plan on receiving your transmissions on?

How do you plan on sending code?  If you just key the transmitter you won't hear morse code in a plain am receiver.

You either have to send a tone and key that or have a radio that has a BFO.  That's a circuit that creates a 300+- tone in the receiver so you can hear code.

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user

I'm just receiving the transmissions with a normal radio receiver, but hacked to receive only one frequency.

I have a 555 circuit set to audio frequency, with the button simply controlling power to the chip.

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4lifenerdfighter (author)2012-04-23

Well, I found this instructable

https://www.instructables.com/id/AM-Radio-Transmitter-using-555-IC-NPN-Transistor/

would something like this be able to transmit... 10 metres?

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