How to improve a FM receiver

[oasis4355]

Hi all,

I've build a FM receiver to receive FM signal from my transmitter. Using a commercial radio i've been able to recieve my FM signal, with a certain amount of distortion.
However, on my FM receiver, i was only able to hear the audio by placing my ear next to the speaker, and the distortion level is unbearable.

How can i the distortion level of my transmitted FM signal? and how can i improve the performance of my FM receiver?

Thanks in advance.

Danny

 

[biff44]

Sounds like you are either way undermodulating the transmitter, and are hearing mostly noise, OR you are way overmodulating the signal, and most of the audio is outside of the IF filter's bandwidth. Try varying the amount of modulation (fm deviation).

 

[oasis4355]

Hi,

Is there anyway i can change the amount of the modulation? Is it changing the Q of the tank circuit?

I've check with a spectrum analyzer, the transmitted FM bandwidth with my audio signal modulated with it, the bandwidth is around 100kHz.

 

[biff44]

Hmmm, that is about what you should have for a commercial broadcast band FM receiver.

I am assuming that you have an audio source that is different from the transmitter. Lomething like an IPOD driving a serarate FM transmitter board. I would adjust the audio output voltage up or down, and this will modulate the Carrier with more or less FM deviation. Try that.

You did not mention if you are sending stereo. Are you?

Also, you need to lowpass filter the audio signals to be less than around 14 KHz, or they will fold over in the receiver and sound like funky distortion.