AM to fiber problems - Electronic Circuits Projects Diagrams Free

Dhamnaghshun · 9th October 2006, 09:38 PM

Hello, looking for a little advice on how to amplify an AM signal without corrupting it, and maybe some extra advice if possible. This is the basic layout of what has been assigned to me.

So far i built the AM mod/demod circuitry using the LM1496 chip(http://www.synthdiy.com/show/showproduct.asp?show=632)

This works fine using a direct connection between mod and demod circuits. But my problem is amplifying this AM signal somehow and putting it through fiber using MFOE71 (http://www.datasheet4u.com/html/M/F/...uctor.pdf.html)

Every attempt at amplifying the signal before sending it to the MFOE71 has totally destroyed the signal. I have been trying to use the LM386 audio amp as the amplifier with no success. The carrier frequency im working with is 200kHz.

The optical detector im trying to use is the MFOD72(([http://www.datasheet4u.com/html/M/F/O/MFOD72_MotorolaSemiconductor.pdf.html)

Trying to piece this together and feel like i have a lot of work left to do.
Any scheme that ive tried to bring the AM signal into the fiber has failed. Any help would be much appreciated on any piece of this project.

audioguru · 10th October 2006, 01:16 AM

You don't show your schematic.
Why did you use an audio amp IC instead of a transistor to drive the MFOE71 optical sender?
How did you connect the LM386 audio amp to the MFOE71 optical sender?
How did you connect the input of the LM386 audio amp to the LM1496 AM modulator?

JimB · 10th October 2006, 03:06 PM

Several things.

I dont think that the LM386 will work at 200kHz. I may be wrong but it is an audio amplifier, not RF.

The MFOE71 has a linear current/light output characteristic.
When you apply your modulated 200kHz carrier to the device, you must also apply a DC bias so that the light output remains in the middle of the linear part of the slope.

JimB

audioguru · 10th October 2006, 04:30 PM

Quote:

Originally Posted by JimB

I dont think that the LM386 will work at 200kHz. I may be wrong but it is an audio amplifier, not RF.

Hi Jim,
In order to have a flat response to 20kHz with its gain at max with 46dB, its response to 200kHz is pretty flat when its gain is only 26dB.

JimB · 10th October 2006, 04:46 PM

OK, fair enough.
JimB

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9th October 2006, 09:38 PM	(permalink)
Dhamnaghshun	AM to fiber problems Hello, looking for a little advice on how to amplify an AM signal without corrupting it, and maybe some extra advice if possible. This is the basic layout of what has been assigned to me. So far i built the AM mod/demod circuitry using the LM1496 chip(http://www.synthdiy.com/show/showproduct.asp?show=632) This works fine using a direct connection between mod and demod circuits. But my problem is amplifying this AM signal somehow and putting it through fiber using MFOE71 (http://www.datasheet4u.com/html/M/F/...uctor.pdf.html) Every attempt at amplifying the signal before sending it to the MFOE71 has totally destroyed the signal. I have been trying to use the LM386 audio amp as the amplifier with no success. The carrier frequency im working with is 200kHz. The optical detector im trying to use is the MFOD72(([http://www.datasheet4u.com/html/M/F/O/MFOD72_MotorolaSemiconductor.pdf.html) Trying to piece this together and feel like i have a lot of work left to do. Any scheme that ive tried to bring the AM signal into the fiber has failed. Any help would be much appreciated on any piece of this project.

10th October 2006, 01:16 AM	(permalink)
audioguru	You don't show your schematic. Why did you use an audio amp IC instead of a transistor to drive the MFOE71 optical sender? How did you connect the LM386 audio amp to the MFOE71 optical sender? How did you connect the input of the LM386 audio amp to the LM1496 AM modulator? __________________ Uncle $crooge

10th October 2006, 03:06 PM	(permalink)
JimB	Several things. I dont think that the LM386 will work at 200kHz. I may be wrong but it is an audio amplifier, not RF. The MFOE71 has a linear current/light output characteristic. When you apply your modulated 200kHz carrier to the device, you must also apply a DC bias so that the light output remains in the middle of the linear part of the slope. JimB __________________ Experience is directly proportional to the value of the equipment ruined.

10th October 2006, 04:46 PM	(permalink)
JimB	OK, fair enough. JimB __________________ Experience is directly proportional to the value of the equipment ruined.