please help!

J

julius1723

New Member

• Jul 2, 2005

• #1

I just finished making my 3v fm transmitter but seems there was a problem because the signal are not stable it operates but suddenly the signal receive by the receiver is lost. would you please help me?

 

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JimB

Super Moderator

Most Helpful Member

• Jul 2, 2005

• #2

I am not surprised.

As soon as you put your hand near to this thing, the stray capacitance will change and the frequency will change as a result.

The antenna is connected directly to the circuit which determines the frequency, move the antenna, change its shape or bring another object near to it and the frequency will change.

C4 is not "optional" it is ESSENTIAL.

The circuit is at best a toy, at worst a piece of junk. I am sorry if this sounds harsh, but that is the reality.

JimB

 

Phasor

Member

• Jul 2, 2005

• #3

...And the battery is drawn the wrong way around.

 

Someone Electro

New Member

• Jul 2, 2005

• #4

The + and - are right but the batery is upside down.How cod thid hapend?

 

mstechca

New Member

• Jul 2, 2005

• #5

julius1723 said:

I just finished making my 3v fm transmitter but seems there was a problem because the signal are not stable it operates but suddenly the signal receive by the receiver is lost. would you please help me?

Click to expand...

This is normal for your circuit, simply because the antenna (doesn't matter what kind it is) is literally hogging the frequencies and sucking the signal out of the transmitter.

I think your best bet is to somehow attach a "buffer amplifier" to where the antenna is supposed to go and that might add stability.

Basically, you can have either high stability, or high range, but not both.

see talkingelectronics.com interative website. They have a whole article on transmitters.

 

J

julius1723

New Member

• Jul 2, 2005

• #6

hey! guys thanks all of youre suggestions ill look this a very big thing that you've contributed to me as a electronics newbie..

 

audioguru

Well-Known Member

Most Helpful Member

• Jul 3, 2005

• #7

It doesn't have a voltage regulator so its frequency will change as the battery runs down too.
After all, that's how it makes FM. By the microphone changing the conduction of the transistor, which also changes the voltage across it, therefore changing its collector capacitance that is connected directly to the tuned circuit. :lol:

 

Thunderchild

New Member

• Jul 3, 2005

• #8

try this it on a site that if u look at the bottom of this page there is a link to it saying that "free electronics circuits" is our friend
https://www.free-electronic-circuits.com/circuits/fm-transmitter.html
try also encasing ur project im a metal box. i had the same problem with something not that different from this: a disaster and 5 minute wonder

 

mstechca

New Member

• Jul 3, 2005

• #9

that sensor is a little too much.

that [bleep] actually meant the word that rhymes with the F-word (swear word), but it starts with S. It's S---U----C-----K.