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decreasing wave frequency with sbl-1 mixer

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Discussion in 'Radio and Wireless' started by jalil92, Jun 7, 2019.

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  1. Jun 7, 2019 #1
    jalil92

    jalil92

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    Jun 7, 2019
    I used sbl-1 mixer for decreasing signal frequency from 3.174 MHz to 10 kHz. The generated signal has high noise level. The butterworth and sallen-key filter was used to eliminate noise, nevertheless there is the noise. There is also the possibility of sending images of the circuit. How can i eliminate the noise?

    Please help me.

    Thank you
     
  2. Jun 7, 2019 #2
    duke37

    duke37

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    The noise must be comming from somewhere. If it occurs with the input signal shorted, then it is due to the heterodyne frequency. This should be clean and preferably a square wave.

    Do you have interference at about 6MHz?
     
  3. Jun 8, 2019 #3
    davenn

    davenn Moderator

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    You have given almost zero info on what you are trying to achieve
    so what is your local oscillator frequency and what is the oscillator circuit?

    you need to show your circuit as well as a photo of the construction
     
  4. Jun 9, 2019 #4
    jalil92

    jalil92

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    Jun 7, 2019
    The function generator was used as an local oscillator. Its voltage (peak to peak) is 5 V and Its current is probably 20 mA . the schematic of circuit is in file attachment.
     

    Attached Files:

  5. Jun 9, 2019 #5
    duke37

    duke37

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    You have shown a block diagram, not a schematic.
    If the Butterworth filter uses active components, then they could introduce noise.
    What was the scope measuring?
     
  6. Jun 9, 2019 #6
    jalil92

    jalil92

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    Jun 7, 2019
    Measurement of phase difference between two signals
     
  7. Jun 9, 2019 #7
    davenn

    davenn Moderator

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    OK, first up, you cannot build RF circuits on breadboards like that and expect them to work
    It would be better if it was just done with point to point wiring and keep ALL wires as short as possible
    Your long wired circuit is going to be picking up RF noise from everywhere. 50/60 Hz mains will be a big issue


    So where is the 3.174MHz RF input signal coming from ?

    Getting a 10kHz product from the mixing is going to be a pretty big ask.
    When I have used mixers like the SBL-1, the RF in and the LO are usually always 100's of kHz to several 10's of MHz apart
     
  8. Jun 9, 2019 #8
    jalil92

    jalil92

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    Jun 7, 2019
    RF input signal is a receiver air coil that works at 3.174MHz frequency. the picture of RF signal is in attachment file.
     

    Attached Files:

  9. Jun 9, 2019 #9
    duke37

    duke37

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    10kHz will be output with either 3174kHz or 3194kHz. The coil will not have a high enough Q to distiguish between these.
    The long wires will enable lots of interference to be received. Such a circuit should be installed in a screened box with an RF input and a feed through capacitor on the output. I would use Veroboard and a much smaller coil with more turns.

    What are you trying to do?
     
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