Simple 200 feet "Morse Code" Tranceiver [closed]

Question

TLDR: I'm trying to create a simple 200 feet range "morse code transmitter" (which is legal according to the FCC), which is really just an AM transmitter that can transmit a single frequency tone (lets say, a nice 400 Hz tone).

What I plan to do is have a pushbutton to allow or block the 400 Hz tone (created using 555 IC) from going into the transmitter, which will allow me to send dots and dashes (by quickly pressing the pushbutton for a dot, or holding it down for a little longer for a dash).

My goal is to keep this circuit very basic (not too many components) so that it is easy to understand and learn from. This means that I also don't need any "quality" features (such as cleaning up sound quality, etc). I'm just hoping for a bare-bones transceiver, so I wanted to ask here for suggestions for a circuit that meets the following requirements:

1. Antenna(s) less than 3 ft (the smaller the better)
2. Can be powered using a 9V battery (or two)
3. The receiver can "play" the received Morse code signal using a DC piezo buzzer or an LED
4. Can transmit to 200 feet (which is legal without a license, according to the FCC)
5. It can transmit at any frequency.

Other than those, feel free to use your creativity. Also, I'm planning to use this in a university setting, which is for educational purposes, which is also allowed by the FCC. Please let me know if you have any questions; I'd be happy to elaborate.

Also, please note that I don't need a Morse code generating mechanism; I'll simply do that using a 555 timer; I just want to learn how to extend its range. From my research and experimentation, I've only been able to transmit around 5-10 feet, and despite weeks of searching, I wasn't able to get it to transmit further.

Lastly, I know that this question is quite similar to this post, but I found the answers hard to learn from, as not much circuitry is discussed.

Answer 1

You're confusing unlicensed with legal I think. It is not allowed to make and use an intentional radiator, even an unlicensed one, that hasn't been certified to comply with FCC Part 15 limits for the frequency it uses.

More here: www.arrl.org/part-15-radio-frequency-devices

From this doc:

"Low-power intentional radiators: Part 15 rules also permit intentional radiators to operate on nearly any frequency. These low-power intentional radiators are limited to specific field strengths that vary with frequency. The field-strength limits were chosen so that interference is not expected under most circumstances. These devices are certificated."

As far as enforcement of such things, it's kind of the 'honor system' when it comes to interference. You're not allowed to make a radiator that interferes with someone else's stuff. If you do, and they call you on it, you are obliged to stop using your interferer.

As a practical matter, something powered from a 9V battery using a 'garbage' band like CB or one of the other unlicensed bands, and that emits less than 50mW or so is unlikely to encounter problems.

Answer 2

any frequency that it is not illegal to transmit at

There's no such frequency, unless you either

• get type-approven equipment and operated in a band specified for that type of transmission (i.e. mostly ISM bands; LoRa might be an interesting technology for you) or
• get a license to some spectrum. What you describe seems to be covered by amateur radio usage, so an amateur radio license would be the right thing to get.

Note that my enthusiasm for Morse is very limited. If you want to communicate with little power over large distances, use modern method with loads of processing gain and channel coding to compensate your low SNR at the receiver. That's how LoRa gets so far.