Understanding the Legalities and Limitations of Building a PM RF Transmitter

[hardyboy16jm]

How can I build a transmitter using radio waves with pulse modulation (Which I think [PM] means sine waves that either transmit or don't)? I can't find anything on how to build a PM transmitter, I can only find FM/AM ones, and I'm not smart enough to convert that information to the way I want. Also, I know that there are many laws concerning using AM/FM (and maybe PM?) radio without correct licensing because they might screw up other stuff, but would a PM transmitter do that? Any help will be accepted. Thank you!

 

[Averagesupernova]

PM might mean phase modulation. Could you give us some more info? Application?

 

[vk6kro]

Pulse modulation is a type of amplitude modulation.

You can achieve it by applying or removing power to the transmitter.

It is used, for example, in radar systems where you want to send a pulse of signal, then listen for an echo. When you are listening for the echo, the transmitter needs to be turned off or you won't hear the much weaker echo signal.

Transmitters sending Morse Code are usually switching on and off like this, too.

Pulse modulated signals can cause interference to other services. They are essentially being modulated by a square wave, so this can cause the signal to be very wide due to the generation of a lot of sidebands

 

[hardyboy16jm]

Actually, I'm going to edit this question a bit. I think that I will use an AM or FM wave, but with what amplitude/frequency can I know that the signal won't interfere with other waves?

 

[vk6kro]

Unfortunately, you can't legally just pick a frequency to transmit on.

If you look on Google, you can find plenty of very low powered FM transmitters which operate on about 90 MHz. You could study how these work, even without building them.

They usually don't transmit further than within one house, so they shouldn't worry anyone.

After that, maybe you could decide why you want to use pulse modulation.

You could get pulse modulation just by connecting and disconnecting the battery on one of these small transmitters.

To answer the question you erased, modulating with a square wave produces many sidebands and a very wide signal, however, if the sides of the square wave are made less vertical, the width is reduced. So, you increase the rise and fall times of the switching waveform and this makes the signal cleaner.

 

[berkeman]

Actually, I'm going to edit this question a bit. I think that I will use an AM or FM wave, but with what amplitude/frequency can I know that the signal won't interfere with other waves?

Is this for your car door lock remote project? It might be best to stick with modifying an IR remote control (TX/RX pair of modules), instead of trying to get all of the RF stuff right. You can focus on how to do the encryption of the data that you transfer from key to lock, instead of having to figure out how to make a legal RF transmitter.

 

[Averagesupernova]

Or you could just buy an aftermarket kit to put on.

 

[skeptic2]

https://www.sparkfun.com/categories/16

 

[Mordred]

Unfortunately, you can't legally just pick a frequency to transmit on.

this is an important concern with RF. Frequency usage and output power of said frequencies is regulated. In Canada its covered and controlled by industry Canada. In the state I do not know.