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  1. #1
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    Built-in SWR bridge and power meter

    I have about 100W PA on fixed frequency under 20MHz this PA works to 50Ohm load.
    Because the load can be disconnected, damaged, dis-tuned I need to track SWR. I need built-in SWR.
    I was looking at this site
    I want to try to reduce the SWR meter to PCB to PA.
    My first shot see pic.
    As toroid I plan use small OD097 MPP (OD 9.65mm, Al=66nH, Perm=125u)
    C1 SMD 1111 NPO 500fF 630V
    R1 SMD 0805 10 Ohm
    D1/2 high speed BAV99W 100V 4ns Cd 1.5p
    Output Ref and Fwd connect directly on 12-bit successive approximation ADC in MCU

    C1 connect on Power line on PCB and turn over toroid realized as short wire PCB - toroid - PCB maybe thin coaxial or only wire or RF rope.

    I am not a radio amateur and so I have no experience with SWR meters.
    how much are we out, what else to do, etc.?

    Click image for larger version. 

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  2. #2
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    Re: Built-in SWR bridge and power meter

    Not sure how you arrived at this circuit. The linked SWR bridge tutorial uses a capacitive voltage divider rather than CR circuit. Are you aware that the circuit must be dimensioned for 500 ohm reference impedance instead of 50?



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  3. #3
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    Re: Built-in SWR bridge and power meter

    Yes it uses a capacitive divider.
    It is SWR applicable to the whole band.
    I will do with a single frequency.
    So I dared to replace the lower C for the resistance R=Xc on my frequency.



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  4. #4
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    Re: Built-in SWR bridge and power meter

    I will do with a single frequency.
    So I dared to replace the lower C for the resistance R=Xc on my frequency.
    Even for a single frequency, the phase relation between voltage and current matters.



  5. #5
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    Re: Built-in SWR bridge and power meter

    You are right on the other side, but it also applies.
    C1/C2 more precise Z1/Z2 is only voltage divider for sampling voltage on line, current is sampled over L1.
    Her is SWR meter where is voltage divider realized only with resistor.
    The disadvantage of this solution is the large power loss on the divider.
    Click image for larger version. 

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    I try realize combined C/R divider from what I have on the table.
    Click image for larger version. 

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    On power line go about 35W on frequency over 10MHz to 50ohm load fo SWR=1 is on C3 minus 1V as swr rises the voltage goes into positive valua and for SWR=5 is over +600mV.
    Her is the best Breune Coupler analysis I found.


    Anyway, is there any variant of diode 1N4148, generally 4ns diode, for voltage 150 or 200V?


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  6. #6
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    Re: Built-in SWR bridge and power meter

    I have two questions about the original SWR design of the bridge by Dominique - F1FRV
    1.Selection of load resistance at bridge voltage outputs
    Click image for larger version. 

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    In original simulation is R5 R3 1M with R2 3,3 Ohm. Discharge 1nF over 1M resitor is need time approximately 5ms .
    I would also like to use the SWR bridge as a disconnected load detector with a response time of 1ms.
    In my design is R2 10Ohm and for faster response need R5 R3 100k .
    That will not be a problem ?

    2. SWR bridge forward output vs output of current transformer?
    In actual design I have diode RF detector for measure Voltage on power line and current transformer for measure current any as see Picture. and MCU use this information for approximate power calculation.
    My question is.
    How much is FBC output of current transformer comparable to the forward output of the SWR bridge?
    Click image for larger version. 

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