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Power supply for a FM transmitter.

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snaider

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I want to build a power supply for a FM transmitter. I have build some power supply with voltage regulator IC(7809) and capacitors at the input and output pin of the IC, but the sound get in the receiver(radio), is the music with a high frecuency noise, but when a use a 9 Volts battery this noise does not appear.
 

IanP

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You can construct a low-pass filter at the output of the voltage regulator. This filter may consist of two 100µH - 1mH inductors on both lines (+9V and 0V) and 100nF ceramic + 10µF tantalum capacitors right at the output.
Also, make sure that you have 100nF capacitors (input-GND and output-GND) mounted virtually on the legs of the voltage regulator.
Regards,
IanP
 

seadolphine2000

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Noise in the audio of an FM receiver, coming from the
FM transmitter, is always associated with the power
supply used with the transmitter. The only way that I
know of...to get rid of the noise...is to use a 9 volt
dc battery.

If you still want to use the power supply, you can do
this....

Put a 47,000uF electrolytic capacitor, in parallel, in
between the power supply and the transmitter.

Always keep the leads short from the power supply and
the transmitter. Also, you may want to shield the
antenna system from the power supply with some sort of
large rectangular metallic shield.

Solder your positive side of the capacitor to the
positive side of the power supply, and therefore,
solder your negative side of the capacitor to the
negative side of the power supply.

These two things will bring down the hummmmm that you
hear in an FM receiver.
This is the answer for the same question you ask a friend told me this. Hope this helps
 

platonas

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If I am not wrong, you have a noise (hum) due to the 50Hz rectification.
To overcome it you need large electrolytics to filter it out. It is the ripple due to poor filtering.

Also full wave rectification is recommented than half wave rect.

At the input of your regulator use electrolytics of 10,000uf.
The size of the capacitor depends on the current needed, but for currents less than 1A the 10000 uf should be ok.
 

jonw0224

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Actually, it sounds to me that since you have a high frequency noise (not low frequency like the ripple from a power supply) and that since that noise does not go away when you power the FM transmitter from a battery, that maybe you have some loose connections between the FM transmitter and power supply(s) or between the FM transmitter and the input signal. I recommend soldering the connections (make sure you don't use excessive solder or let the solder crystalize). You can find many websites about soldering.

Of course, your problem could be in the FM transmitter as well.
 

seadolphine2000

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but when a use a 9 Volts battery this noise does not appear.
Mr jonw0224,..

The noise disappear on using the battery, thus the noise is due to the power supply.
 

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