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  1. #1
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    Simple RF power watmether?

    I have a question about measuring RF power.
    Have RF source 10MHz 0-100W , this works to Z load , if Zload is R=50 everything is sunny and Pout=U^2*R,
    In this case, but Zload change impedance with temperature (significantly] the part of the performance is reflected back to the source
    Therefore it is between source and load, SWR meter 2 or in more expensive 1. (If SWR exceeds 5, source si power down]
    But what if I want to measure the actual power delivered to the load?

    If I search RF watt meter I find many construction with AD8307 3 , but this measure only voltage and presumes 50 Ohm load.
    The solution is digital vector RF Wattmeter but this is for my complicated and expensive.

    Is possible add current sense transformer, 4 and P=U*I when U=DC voltage form 3 and I=DC voltage from 4 ?
    Or maybe somehow use information from 1 or 2 SWR?
    Advise how to easily and cheaply measure output power?

    Click image for larger version. 

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    •   Alt27th May 2018, 10:38

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  2. #2
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    Re: Simple RF power watmether?

    A Convenient Directional Coupler will be the solution at this range of power.I don't know the operating frequency but I presume the frequency of interest is not too low.
    Directional Coupler will allow you to measure the Incident Wave and Reflected Wave Powers simultaneously.



    •   Alt27th May 2018, 12:47

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  3. #3
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    Re: Simple RF power watmether?

    The original post says 10MHz so a directional coupler might be too large unless it can be fabricated with bulk components.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



    •   Alt27th May 2018, 16:13

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  4. #4
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    Re: Simple RF power watmether?

    OK, I didn't see the frequency was 10 MHz.
    Yep, the Directional Coupler will be bulky and expensive at that frequency.I think "Bird Wattmeter" that is very famous in Radio Amateurs can be an option.
    The second hand price is around 200 $ and I believe it's reasonable.There are other handy-made modules but I don't know their uncertainties.



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