RF electronics

[Lynx516]

I am looking at designing a basic walkie talkie and basically I have a good knowledge of digital cuircuity and reasonable analog cuirtuity but I have no idea with radio cuircuitry. Does any one know where I can start with this?

 

[rjain]

I had a $25 electronics kit from Radio Shack that taught me about basic AM circuits when I was a 10 year old.

I'm sure your local library will have a few books with this kind of material...

 

[Geniere]

A basic radio is pretty simple circuitry. To transmit, you need an oscillator that runs at a reasonably high frequency to keep antennas short. Amplify and modulate the RF so it changes amplitude based on a microphone input. Connect to a tuned (rc, parallel) circuit (resonates at your oscillator frequency) connected to an antenna of ½ wavelength.

To receive, duplicate antenna and tuned circuit, demodulate (diode detector), amplify to drive speaker.

There is no frequency regulation so make your tuned circuits very broadband (low Q) and the receiver will have to be tuned as the frequency drifts around. Adding crystals will help to stabilize oscillator.

I?m not a radio buff, but I would bet there are single component (chips) that do all the work for transmitting and receiving. You?d only have to add a crystal and antenna.

I don?t know if Ham radio forums exist. If they do, that?s where I?d go.

 

[blahblah99]

What the guy above me said.

There are different types of modulation techniques, but the easiest and most common are AM and FM. There ARE modules out there that'll transmit voice data over AM/FM for cheap. Or you could be ambitious and design your own tuned amplifier/receiver modulated on a carrier frequency of your choice. Of course, you will also get the attention of the FCC.

 

[Jarhead]

Try the ARRL Handbook, found at every decent bookstore, and nearly all libraries.

 

[Pudgygiant]

Before you test it I'd look at the FCC regs for transmitters... if you impede a reserved bandwidth they'll hit you with fines so big your back will crack under the load...

 

[dkozloski]

Don't get too worried about getting caught by the FCC for stepping on anyone elses toes. They quit actively monitoring for miscreants years ago and now work only on complaints for malicious acts like messing with aircraft communications or navigation. Having said that, if you stay in the so called citizen band frequency ranges you should be okay. For quite a while now it has been anything goes. Any good technical bookstore stocks "How To" books with circuit diagrams that reduce your task to parts procuring and assembly. You will be needing some bench gear like a good RF voltmeter and an oscilloscope with a detector probe and possibly a frequency counter if you expect to get much beyond the $9.95 Toys 'R Us level of performance. This should be a great learning experience. You might also check into local amateur radio operators in your area. I am sure they would be more than willing to help you.

 

[kb9skw]

I dont think he will be having any issues with the FCC or finding the ARRL handbook in his local book store as he is in the UK.

Take a look at the Flight Refuelling Amateur Radio Society over in the UK. Excellent sorce of information for us hams.

 

[mAdD INDIAN]

Originally posted by: Pudgygiant
Before you test it I'd look at the FCC regs for transmitters... if you impede a reserved bandwidth they'll hit you with fines so big your back will crack under the load...

how could they ever catch you?

It's not like they have IP addresses to trace you to your ISP.

 

[DrPizza]

Originally posted by: mAdD INDIAN

Originally posted by: Pudgygiant
Before you test it I'd look at the FCC regs for transmitters... if you impede a reserved bandwidth they'll hit you with fines so big your back will crack under the load...

how could they ever catch you?

It's not like they have IP addresses to trace you to your ISP.

They could catch you while you were transmitting.

 

[kb9skw]

Originally posted by: mAdD INDIAN
how could they ever catch you?

It's not like they have IP addresses to trace you to your ISP.

Are you kidding me? The RDF center in th UP of Michigan can pinpoint a hand held radio to a part of a city anywhere in the country. then a they just need to send a field agent or ask the ARRL to have its Official Observers do it for them.

Do you know anything about RF at all?

 

[Lynx516]

Thanks for the info guys proving to be very helpful

 

[mAdD INDIAN]

Originally posted by: kb9skw

Originally posted by: mAdD INDIAN
how could they ever catch you?

It's not like they have IP addresses to trace you to your ISP.

Are you kidding me? The RDF center in th UP of Michigan can pinpoint a hand held radio to a part of a city anywhere in the country. then a they just need to send a field agent or ask the ARRL to have its Official Observers do it for them.

Do you know anything about RF at all?

nope I know nothing about it. That's why I was asking. How can they pin pointed? It seems interesting. Do they do some sort of triangulation?