swr meter mod

Discussion in 'Wireless & RF Design' started by ninjaman, Jul 23, 2014.

  1. ninjaman

    Thread Starter Member

    May 18, 2013
    306
    1
    hello

    I have an swr meter, its a team 1180-p
    http://www.pjbox.co.uk/swr-team-cb-swr-meter-1180p-26-30-mhz.html

    I am using a ft817 5 watt with power supply, 2.5 watts with battery.
    I can get full scale deflection when using 5 watts, though the power is half what it should be.
    there is a 10watt and 100 watt switch on the meter. I can only use the meter on 10 watts. im guessing that the meter is showing half the power im putting in because it expects 10 watts instead of 5.
    is this correct?
    I think that it has something to do with the power formula and the squared bit in it. (v^2/r)
    is there a way to modify the meter to get it to show the correct power in.

    thanks
    simon

    RIMG0063.jpg

    RIMG0056.jpg
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    I think you first need to ascertain whether in fact the power source is as you assume using some more reliable, independent measurement. Then it is appropriate to compare that measurement with the 1180 which is likely not a precision power measuring device. What you measure with is as or more important than what you are measuring. I am also doubtful that the 1180 works properly on a milk chocolate base. Dark chocolate would be much better.
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    why not use the built in swr function of the ft817? I have found mine to be accurate.
    the cb style swr meter is probably optomised for 27 mhz, and not the range covered by the 817.
     
    Last edited: Jul 24, 2014
  4. ninjaman

    Thread Starter Member

    May 18, 2013
    306
    1
    hello

    I don't yet have an RF probe, I thought that may be one way. I don't have an oscilloscope that will go up to 30MHz. I don't have a separate watt meter.
    is there some other way to measure the output power?
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Might try Osmosis.
     
  6. PRFGADGET

    Active Member

    Aug 8, 2011
    50
    7
    Check the "Team" meter (and the radio) against a "known good" meter such as a "BIRD 43" or some other known good meter at the frequency's in question.
    The SWR function is pretty basic to all such meters, if you have enough power to get the unit to "CAL" and then switch to "read" and have indication then it is probably close enough , you can do this and then REVERSE the coax cables and try again , if in the reversed mode you get the same amount of deflection (or very near) the SWR function is good.
    Generally speaking, MOST CB watt meters are not very accurate especially out side of their design range (11 meters) , they may function on 10 and 15 meters but don't expect much, this is due to component choice and matching.
     
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