Make a radio transmitter...

[ski_power]

We're having a contest on building a radio transmitter.

 

The criteria is simple. Build a transmitter that sends voice, which can be tuned on a certain radio frequency nearby.

It's got to be cheap and the parts must be easily available.

 

So how do I go about it.

 

P.S. The cheapest and the most effective one wins.

[YT2095]

Hmmm... a 2n2222, 2x 10kR, 2x 47pf, a 10 turn copper loop, a 2n2 cap, a variable cap (for tuning), 100R will make the transmit carrier.

 

through a .01mfd cap to the base of the 2n2222 with a powered electret mic, you`ll get a good half a klik distance on a quarterwave twig!

 

edit, what freq are we talking here, as this is an FM transmitter (dirt cheap, but I can make one cheaper depending on the freq) )

[ski_power]

what's 2n2222, and all?

 

Can you explain it in full?

[YT2095]

if my camera server was working I`de gladly post a diagram for you, it aint

 

but a 2n2222 is an NPN transistor working freq up to 200Mhz at a good 150mw free air disipation.

 

the circuit is simple, so I`ll TRY and explain it in text (I might be able to do it).

 

imagine the 2n trans leads Emiter Base Collector.

 

the 100r goes to the emiter and the other end of the 100r goes to (-)

 

from the Collector you atatch one side of the 10 turn coil and the other side to the (+)

across this coil you attatch the variable capacitor.

 

from the Base you attatch one side of each of the 10K resistors, one end goes to (+) and the other end of the second resistor goes to (-)

across each of these 10k resistors goes the 47pf capacitors.

 

the 2n2 capacitor goes between the Emiter and the Collector.

 

atatch a wire (about half a metre long directly to the Collector (that will be your antenna).

 

clip the 9Volt battery to the (+) and (-) and you should be transmiting quite a powerfull signal!

 

how`s that?

[ski_power]

Ok, I'll try it out soon.

 

Yeah now they tell that it's got to be FM 95 or 96, as they're not sure. So I guess I'll need to make the vario-one.

[YT2095]

use 4 to 6 turns in your coil for that freq range then, roughly the circumference of a round pencil, moving the coil spacing between winds with the variable cap at center position, until you`re close to 95-96 Mhz then use the var-cap to fine tune

[ski_power]

ok, so now where does the mic go...

[ski_power]

 

Is it more or less like this???

[YT2095]

you only need a single 9v battery.

the 47pf caps go across the 10k resistors.

the variable cap goes across the coil.

 

Hmm... this could take forever

 

I`ll see if I can find a way to draw on this `puter (I`ve never tried it before).

[YT2095]

aha! nevermind, I couldn`t get the hang of drawing, BUT, I did find a cct diag for you that`s even lower on the parts count

 

http://www.uoguelph.ca/~antoon/circ/fmt2.htm

 

and a whole range of others from here: http://www.commlinx.com.au/transmitters.htm

 

I`m sure you`ll find at least ONE that will be ideal for your needs