fm transmitter coil

[monkeytree]

i know this is a popular subject
how much can the coil in a fm transmitter?

 

[stevez]

I don't understand your question. Please restate your question.

 

[monkeytree]

in this schematic does it matter what thickness the wire in the coil is?

 

[Nigel Goodwin]

in this schematic does it matter what thickness the wire in the coil is?

Not to any great extent, however is needs to be thick enough to be self suporting, and not easily damaged.

 

[monkeytree]

in this schematic does it matter what thickness the wire in the coil is?

 

[audioguru]

That FM transmitter doesn't have a variable capacitor to tune its RF frequency. The only way to tune it would be to change its antenna's length or distance from something, its temperature, its battery voltage or the spacing between the turns of its coil. If the wire for the coil is too thick, you wouldn't be able to squeeze the turns closer to lower the tuned frequency.

 

[chemelec]

JUST AN ADDITIONAL NOTE:
And Too Small of wire Will Cause Frequency Drift.

A 18 to 20 AWG is usually Pretty Good Size.

 

[monkeytree]

where would the varible capacitor go?
what are easier to understand values of 15p and 3.3p?
how do you increass the transmitters range?
thnks for help

 

[zachtheterrible]

where would the varible capacitor go?

replace the 15p capacitor with it

what are easier to understand values of 15p and 3.3p?

I don't understand that quesiton.

how do you increass the transmitters range?

Increase the voltage, but i wouldnt go more than 12v. Decrease the 470 ohm resistor, find the correct length for antenna (this can be done by starting out with a long antenna, then trimming it until you get optimal range, this will cause a change in frequency though)

 

[audioguru]

You can also increase the range of the transmitter by adding a single transistor amplifier to the output of the oscillator. Besides increasing the range, the extra transistor reduces the frequency drift because then the oscillator no longer has the antenna connected directly to its tuned circuit.

 

[monkeytree]

You can also increase the range of the transmitter by adding a single transistor amplifier to the output of the oscillator. Besides increasing the range, the extra transistor reduces the frequency drift because then the oscillator no longer has the antenna connected directly to its tuned circuit.

how would i do this i want to do it properly because my friends want ones as well :twisted:

 

[audioguru]

There are lots of ways to add an output amplifier transistor. This guy has a circuit that is very similar to yours. Look at his printed coil with a tap on it:

 

[audioguru]

I made mine like this:

 

[monkeytree]

what is the range on yours/the other one?

 

[audioguru]

I measured a range of about 1km line-of-sight to a good car radio on my FM transmitter, and the author of the other one reports a range greater than 1km for his "under ideal conditions". His projects are here:
**broken link removed**

 

[monkeytree]

so whose should i go for?

 

[audioguru]

Mine has a few more parts but sounds much better! :lol:

 

[monkeytree]

okay

 

[zachtheterrible]

You can also get more range by using a more sensitive receiver. Of course the more sensitive your receiver, the easier it will overload because of strong local stations.

Im still trying to figure out how to make myself an extremely sensitive receiver for use with a small bug. I guess i just have to learn how receivers work first (which im in the process of :lol: )

 

[audioguru]

Of course the more sensitive your receiver, the easier it will overload because of strong local stations.

Not necessarily true, Zach.
A good receiver has a tuned circuit ahead of its RF amp, and has automatic gain control applied to the RF amp to prevent overload.
I can use my simple but good car radio right beside a 100,000W station's transmitter and it works fine to pickup distant stations. My clock radio or Walkman? Forget it.