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How to restrict side bands in Direct Modulation of RF (Analogue) signal

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(joined October 2014)
Participant

Hi every one !
Hope u all are fine.

I am working on Direct Modulation of RF signal with CW laser. The frequency of RF signal is 12.5 GHz and Bit rate is 128 Mega bits/sec.

When i directly modulate RF signal with CW Laser (a component in Optical transmitter library) ” then i got number of side bands as shown in below figure.1 (i have used “sample per bit = 64” here in this case).

Now problem is that i need only three side bands on right side of center frequency and three bands on left side of center
frequency but i don’t know how to reduce side-bands to only three on both sides of center frequency.

I have also tried the above case with sample per bit = 32 and the number of side bands i got is shown in fig.2.
I have also done the same scenario by varying the amplitude of RF signal but that does not effect much on side bands.
I have also attached the components i have used in my case as shown in figure.3.

Kindly guide me if anyone know the solution or how to resolve the above problem. I will be very thankful to you for your this act of kindness.

Best Regards

Responses (3):

    • #17200
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      Ibn Aziz
      Participant

      Hi every one !
      Hope u all are fine.

      I am working on Direct Modulation of RF signal with CW laser. The frequency of RF signal is 12.5 GHz and Bit rate is 128 Mega bits/sec.

      When i directly modulate RF signal with CW Laser (a component in Optical transmitter library) ” then i got number of side bands as shown in below figure.1 (i have used “sample per bit = 64” here in this case).

      Now problem is that i need only three side bands on right side of center frequency and three bands on left side of center
      frequency but i don’t know how to reduce side-bands to only three on both sides of center frequency.

      I have also tried the above case with sample per bit = 32 and the number of side bands i got is shown in fig.2.
      I have also done the same scenario by varying the amplitude of RF signal but that does not effect much on side bands.
      I have also attached the components i have used in my case as shown in figure.3.

      Kindly guide me if anyone know the solution or how to resolve the above problem. I will be very thankful to you for your this act of kindness.

      Best Regards

    • #17205
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      Ibn Aziz
      Participant

      if any one know any other technique which involves Direct Modulation of RF signal with CW laser and results into 3 side bands on both side of center frequency, plz share.

      Best Regards.

    • #17208
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      Abdallah Ismail
      Participant

      Why didn’t you try to use a band-pass filter to get the band you like in your comb generator?

      +1
    • #17212
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      Ibn Aziz
      Participant

      Thanks Abdallah for ur kind response.
      Yes, Abdallah i can get by using band pas filter but i am not using it because i want to make cost efficient system which includes as less components as possible. Therefore i am trying to acquire desire side bands by using optical processing techniques (on the components as shown in fig.3 attached above) rather then using any optical components preferably.

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