Problem with hobbie FM Radio transmitter

bmattias · 15th August 2008, 09:44 AM

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 · 15th August 2008, 03:08 PM

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 · 15th August 2008, 06:02 PM

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 · 19th August 2008, 06:34 AM

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_St...ransmitter.php

Mattias

Iain McNeill · 19th August 2008, 05:51 PM

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

15th August 2008, 09:44 AM	#1
bmattias diyAudio Member Join Date: Aug 2008	Problem with hobbie FM Radio transmitter 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

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15th August 2008, 03:08 PM	#2
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	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?

15th August 2008, 06:02 PM	#3
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	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.

19th August 2008, 06:34 AM	#4
bmattias diyAudio Member Join Date: Aug 2008	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_St...ransmitter.php Mattias

19th August 2008, 05:51 PM	#5
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	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

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