Radio transmitter and receiver

Thread Starter

k1ng 1337

Joined Sep 11, 2020
235
Hi,

As part of an ongoing project for a remote control vehicle, I wish to design my own transmitter and receiver. My goal with this project (along with many others) is to create my own "Frankenstein's monster" with as many basic components as possible. I have an understanding of basic radio theory and have made use of 2.4ghz transceivers as well as a Bluetooth module. I understand that my design will function poorly and with limited range. I am not looking for circuits, rather general information on how to approach the theory.

Let me begin with my understanding on which basic principles must be implemented. I have some experience modulating analog signals so I will assume I can successfully modulate the signal at the transmitter and demodulate at the receiver. For ease of this thread I simply want to send and receive one frequency that is either on or off.

Transmitter: Signal of adequate power is connected to either a terminated branch of one or more wires (like a tree) or in a loop. The spatial geometry of this conductor among one or more axis must be in some multiple of the baseband frequency as to not attenuate the signal before it "exits" the conductor. As current flows in the circuit, some of this energy will radiate into open space either directionally or omnidirectional and is then available to all receivers in range before the signal is attenuated beyond recognition.

Receiver: A resonant circuit is formed at the desired frequency. As the transmitted frequency interacts with the circuit in open space, a tiny current will be induced into the circuit for as long as the frequency is transmitted. The signal is then available for amplification and demodulation.

Is my understanding reasonable? If so I would like to continue with some mathematics. Please feel free to lecture at your leisure.

Regards,
Mark
 
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Papabravo

Joined Feb 24, 2006
17,614
Your information is rudimentary and wholly inadequate for experimentation in the 2.4 Ghz. band. Depending on the power levels involved it may also be illegal. You could end up doing time in the federal slammer. The right way to go about this is to get yourself an amateur radio license which you can do by taking a 35 question multiple choice examination. This will allow you to experiment with stuff at lower frequencies where layout and expensive instruments are not necessarily required. That's my advice, but feel completely free to ignore it. I'm happy to discuss this in more detail if you're interested.
 

Yaakov

Joined Jan 27, 2019
4,023
I'd suggest you take a look at this very helpful training film produced by the Air Force in the 1940s. It does an excellent job of laying out the basics.


In the absence of a ham license, as suggested by @Papabravo, you will be severely constrained by the law concerning building any practical devices. The most likely possibility is under CFR Title 47 § 15.235 using the 49MHz band. The other option is VLF and not practical for remote control.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
235
Thanks for the replies, I especially enjoyed the part about being rudimentary and wholly inadequate which was my suspicion. I am aware of the legalities and I have looked into a operators license but since this is for a small part of the project I will return when better educated, if at all.

Thanks :)
 

Papabravo

Joined Feb 24, 2006
17,614
Thanks for the replies, I especially enjoyed the part about being rudimentary and wholly inadequate which was my suspicion. I am aware of the legalities and I have looked into a operators license but since this is for a small part of the project I will return when better educated, if at all.

Thanks :)
To clarify what I wrote in post #2 a bit. The problem with the portion of the RF spectrum above 450 MHz is that lumped components like inductors, capacitor, and resistors stop behaving like they are supposed to and exhibit contrary behaviors. The main tool for characterizing parts is the VNA (Vector Network Analyzer). They used to cost in excess of a typical middle class house. If you don't know what microstripline design is then this portion of the RF spectrum will remain pretty much out of your league.
 

KeithWalker

Joined Jul 10, 2017
2,095
It is legal to transmit on the 27MHz band up to a max of 100 milliwatts which would be more than enough for your application. The band is shared by CB radio but there is very little activity on it nowadays and the frequency CB radio transmissions are crystal controlled and limited to defined frequencies spaced 10KHz apart. I have included a url which shows some details.
https://www.rightchannelradios.com/blogs/newsletters/cb-radio-frequencies-and-channels
For best success of your project I recommend that you purchase pre-assembled transmitter and receiver modules unless you have experience in designing RF circuits. Here are some inexpensive examples:
https://www.aliexpress.com/w/wholes...board&ltype=p&SortType=default&page=1&CatId=0
 

DickCappels

Joined Aug 21, 2008
8,169
And then there the other ISM bands, but as already pointed out, much below 11 meters the antenna get pretty large and inconvenient for many kinds of remote control. Then there is optical communications which is not regulated in most parts of the world.
 

mlewus

Joined May 1, 2020
1
Thanks for the replies, I especially enjoyed the part about being rudimentary and wholly inadequate which was my suspicion. I am aware of the legalities and I have looked into a operators license but since this is for a small part of the project I will return when better educated, if at all.

Thanks :)
This is the entire reason that commercial RF modules were developed. In 1981 I developed a commercial radio transceiver for a digital communications project. The FCC qualification process was lengthy, intensive, and required very expensive equipment and specialized engineering knowledge. 2.4GHz is far more difficult due to the way that microwaves behave in a physical circuit. You can't just dead-bug or breadboard it and expect it to work, the way you can at lower frequencies.

Licensed hobbyists often look to aarl.com as a source of books and such for ham radio. But ham bands require a license, even though it is today only a short test, no Morse code proficiency as was required in my day.

In today's market you can buy a radio transceiver for a couple dollars at any legal frequency and power, and some non-legal ones. You can be sure that it has been qualified in such a way that if you use it as instructed by the manufacturer you won't end up in jail. And your project will work.

Alternatively, you could do what Marconi did and just set up a sparker with a big coil of wire. And see how long it takes the FCC to pay you a visit :<)
 

Papabravo

Joined Feb 24, 2006
17,614
This is the entire reason that commercial RF modules were developed. In 1981 I developed a commercial radio transceiver for a digital communications project. The FCC qualification process was lengthy, intensive, and required very expensive equipment and specialized engineering knowledge. 2.4GHz is far more difficult due to the way that microwaves behave in a physical circuit. You can't just dead-bug or breadboard it and expect it to work, the way you can at lower frequencies.

Licensed hobbyists often look to aarl.com as a source of books and such for ham radio. But ham bands require a license, even though it is today only a short test, no Morse code proficiency as was required in my day.

In today's market you can buy a radio transceiver for a couple dollars at any legal frequency and power, and some non-legal ones. You can be sure that it has been qualified in such a way that if you use it as instructed by the manufacturer you won't end up in jail. And your project will work.

Alternatively, you could do what Marconi did and just set up a sparker with a big coil of wire. And see how long it takes the FCC to pay you a visit :<)
So it seems we have a new form of gambling called FCC-Roulette. Roll the dice and see how long it takes them. The good news is that like the IRS, the FCC has endured several years of budget cuts, so pays yer money and takes yer chances.
 
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