how do you make a small broadcasting antenna?

[MrDudeMan]

i want to output sound from my laptop headphone jack and feed it into something that will send radio waves a short distance at a certain frequency. on the other end, i want to be able to pick up that sound with a regular radio. this is easily done with kits that overpower the radio station power at close range, but i want to figure out how to make one. anyone know where to start or a good guide? ive been searching google and i am still doing that btw.

btw, this is not a school project.

Text

 

[PottedMeat]

depending on how good with electronics/RF you are you will probably be better off just buying one of those small FM transmitters. If you want to do it yourself you gotta find a way to get the baseband ( 20hz-20Khz mono) signal up to a FM frequency (~88-108MHz) One way to do this is to have a simple transistor oscillator operating at the desired frequency ( say 100MHz) that can be tuned about that point depending on the voltage applied to a device (maybe a variable capacitor in the tuning circuit) The output of the transistor gives a frequency modulated output centered about 100MHz. Hook up a suitable antenna - maybe a wire a few feet long, and tune the receiver. Stereo transmission is another matter...

 

[MrDudeMan]

mono sound is fine. there will only be 1 speaker outputting sound on the other end. AM or FM radio is also fine. the span will be less than 10 feet, and probably less than 5.

i found this, dunno how good it is... Text

 

[FrankSchwab]

By far your best bet is one of the FM Modulators sold to connect portable CD players, iPods, etc., to your car stereo. 10 feet is about the maximum range you can expect (and that's 10 feet to the antenna, not 10 feet to the radio). They're in the range of $20-$30, for example Here.

If you're not good at electronics, building from a circuit diagram will be an unsuccessful experience. You could start Here for a broad selection of circuits.

Radio Shack or Outpost probably sells a kit that would be much more successful.

/frank

p.s. Sorry about that; I didn't read close enough to notice that you already knew about the kits and were looking for more in-depth information. Try the link in the second paragraph; don't worry about building the 1-watt plus monsters.

 

[MrDudeMan]

Frank, first let me say thanks for your advice.

i want to build one to learn how to do it. i also want to use it for something, but the main focus of this project is to understand how to build this type of circuit.

edit: let me add that i am in school to be a CE. i am quite capable of building circuits from a schematic.

 

[AbsolutDealage]

Just a little FYI, the circuits provided on your link (http://members.shaw.ca/roma/three.html) are certainly falling within under the blanket of licensing by the FCC. Make sure that you keep it <1/4 watt to stay out of everyone else's airspace.

 

[MrDudeMan]

Originally posted by: AbsolutDealage
Just a little FYI, the circuits provided on your link (http://members.shaw.ca/roma/three.html) are certainly falling within under the blanket of licensing by the FCC. Make sure that you keep it <1/4 watt to stay out of everyone else's airspace.

i will, but if it helps, its going to be inside of a science building with several feet of concrete on every side and magnetic shieding in the walls of a few of the adjacent rooms.

 

[JTWill]

http://www.rfcafe.com/references/electrical.htm
RF Cafe - Electrical Conversions Formulas & References
go throught the antenae section and bookmark this for all future info.massive amount of info here

 

[KingPhil]

I heard soemthing stupid about making a hi-powered WIFI antenna by using a pringles can and a wireless card.

Sounds ridiculous to me........ never tried it........ guess its supposed to direct teh WIFI waves into a much more direct path.....

 

[MrDudeMan]

thanks for the links/help

 

[harrkev]

Originally posted by: KingPhil
I heard soemthing stupid about making a hi-powered WIFI antenna by using a pringles can and a wireless card.

Sounds ridiculous to me........ never tried it........ guess its supposed to direct teh WIFI waves into a much more direct path.....

This is just a very crude type of antenna. It might be ghetto, but it works!

 

[KC5AV]

Originally posted by: harrkev

Originally posted by: KingPhil
I heard soemthing stupid about making a hi-powered WIFI antenna by using a pringles can and a wireless card.

Sounds ridiculous to me........ never tried it........ guess its supposed to direct teh WIFI waves into a much more direct path.....

This is just a very crude type of antenna. It might be ghetto, but it works!

It would certainly be ghetto, and I'd question how efficient it would be.

 

[MrDudeMan]

Originally posted by: KC5AV

Originally posted by: harrkev

Originally posted by: KingPhil
I heard soemthing stupid about making a hi-powered WIFI antenna by using a pringles can and a wireless card.

Sounds ridiculous to me........ never tried it........ guess its supposed to direct teh WIFI waves into a much more direct path.....

This is just a very crude type of antenna. It might be ghetto, but it works!

It would certainly be ghetto, and I'd question how efficient it would be.

it works extremely well. i made one and i can get access from anywhere on my school campus from my dorm's wireless network. it is well over 400-500 feet from the dorm, and the signal is not very strong, but it works.

 

[JTWill]

this ant. your talking about is called a Horn ant. And it would be better to use a device that is tuned for the frequency you have. A tuned yagi ant. would give you better than 500' easy.

 

[RelaxTheMind]

a basic transmitter. Radio shack used to carry a "build it yourself kit" for a while. If they dont have it anymore I may be able to remake a circuit diagram. stereo output would be like 4 times as much circuitry for the extra stages.

The other hard part is getting your hands on the variable inductors/capacitors to get the frequency that your looking for.

In regards to the antenna stated above. It has now being called a cantenna they work fine but are too directional. I made this antenna out of old power wire, scrap car antenna wire, and some sheetmetal i had laying around...

http://martybugs.net/wireless/biquad/

it had better range/coverage area than my homemade cantenna. (much better for wardriving in the car)

Both of which are useless as i fried my orinoco wireless card and opted for internal minipci card.