Problem with hobbie FM Radio transmitter

[bmattias]

Hello!

I've build a little FM radio transmitter to broadcast music around the appartment. It is powered by a 1,5V battery.
When I connect it to my MP3-player it sounds good, but when I connect it to my computer to broadcast iTunes I get a lot of buzz. It is like the signal is getting a lot weaker but it sounds good otherwise. So I just want to get rid of the noise.
Any suggestions?

thank you very much!
- Mattias

 

[Iain McNeill]

My first guess would be RF interference from the PC upsetting your transmitter. Try moving the transmitter around or distance it with longer cord.

Can you post the schematic? Is it a chip based transmitter or discrete?

 

[DigitalJunkie]

You can also try some small ferrite beads on the audio leads,and some small bypass caps,470pf or so.
I've noticed alot of HF 'hash" coming from PC soundcards,some simple filtering usually helps.
Putting your transmitter in a metal enclosure might be good also.

 

[bmattias]

Thank you very much for your quick respons. I have not had the time to try out your solutions yet but I will.

here is the link to the schematic:

http://electronics-diy.com/BA1404_Stereo_FM_Transmitter.php

Mattias

 

[Iain McNeill]

Hi,
I see some more problems:

-no ground plane
-unshielded L1 will pick up EMI and feed into modulator
-unfiltered antenna output

Putting this is a metal enclosure with ferrites on the I/O wires as DJ suggested will help considerably.

good luck