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Converting CB Watt/SWR meter to 40m

Discussion in 'Home Brew' started by Jim Dickey, Aug 9, 2017.

  1. Jim Dickey

    Jim Dickey
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    I have a ASTATIC 10/100w meter that was orginally designed for the 11m band. I have a better one for CB now, and would like to use this one to test 40m QRP amps and transceivers. Super accurate isn't important, I just need to be able to prove that I am making positive changes when I build or modify something.



    I'm thinking this should be as easy as swapping a coil inside?
     

  2. Robb

    Robb
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    Not unless you have the means to re-calibrate it too.
    Just buy a Daiwa and be done with it.
     
    Tallman likes this.
  3. Jim Dickey

    Jim Dickey
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    Is it going to be far enough off that the needle wont move? I have a few QRP rigs that put out 5w CW that could be used to calibrate.

    Like I said I don't need any real accuracy, I thought the home brew forum was the right place to post this.
     
  4. Captain Kilowatt

    Captain Kilowatt
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    Just try it on 40m. You might be pleasantly surprised. Most CB power meters have a small pc board with a straight thru strip from input to output and a strip on either side for forward and reverse pickup. There are no coils to sub out. If you do not need great accuracy it my be functional for what you want already.
     
  5. Beetle

    Beetle
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    If nothing else, it will give a "relative" indication.
     
  6. vkrules

    vkrules
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    It should work.But you might need more drive to get FSD . I.E you might need 20w to get it to read 10. .

    Thinking if it is a dual range 10 and 100 you will have 4 trim pots ( variable resistors ) 2 for each range fwd and reverse. Would be real easy to recalibrate.

    Depends on the layout of your particular meter.
     
    #6 vkrules, Aug 13, 2017
    Last edited: Aug 13, 2017
  7. Paul-W5lz

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    Try it and see what happens. It'll probably work fine. If it's off a bit, do you really think it's going to make much/any practical difference? I don't. If you recalibrate, what do you recalibrate against? If that meter is right to about 10%, that's as good as it gets (even those Birds).
     
  8. Jim Dickey

    Jim Dickey
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    It worked great. Made some adapters for BNC to PL259 and plugged it in. The 40-Niner was reading about 300mW, the Super Rockmite was reading about a watt and a quarter. The amp I built (that IRF840 diagram that claims 60W out) is putting out zero watts. Gave me the info I needed at this point.

    Just need to figure out why the amp no worky.
     

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