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Flex 6400M SWR Bridge accuracy

My 6400M’s SWR meter shows roughly 1.3:1 when directly connected to two different Bird Termaline loads that don’t cause any visible meter deflection on my other rigs. The 6400M does have the internal ATU, which is obviously not engaged when testing.

What should the nominal accuracy of the meter be?




  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    The SWR Bridge is calibrated during its build cycle and it should be the same as your Bird watt meter. You might want to try a lower power slug on the reflected power on the Bird.

    Also, try measuring into a 25 ohm resistive load (2 dummy loads in parallel) and see what you get for a reading on both meters.

    If you feel your SWR meter on the radio is not correct and the radio is under warranty, you may wish to open a support ticket.

    This is good article on SWR readings.

  • N7CXI
    N7CXI Member ✭✭

    Thanks, Mike.

    There’s no question the meter isn’t accurate, I was just looking for the normal variance.

    The rig is not in warranty, so I’ll probably just ignore it for now. If it gets worse to the degree that it affects operation, I’ll send it in for repair.

    Your comment about putting two loads in parallel is interesting, and might help me hazard a guess whether the error in the coupler is resistive or reactive. I’ll bet three macaroni on resistive.

    FWIW, the Bird loads I mentioned don’t have integrated meters. I connected each load to the 6400M ANT1 port with a 6” piece of known good RG142, and observed the meter on the 6400M only. The 6400M reads 1.3:1 , while 7000DLE MKII, a TS890S and a FT-710 all read “flat” when connected in the same manner and tested with each of the two loads independently.


    Jim N7CXI

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Keep in mind Bird Watt meter accuracy.

    It is 5% of the full scale reading of the slug.

    That means that a 100 watt slug can be off as much at 5 watts at all areas of the scale. It means that a 20 watt RF level could be considered accurate 15 and 25 watts.

    Welcome to the challenge of having 2 pieces of test equipment. Which one is correct? :)


  • N7CXI
    N7CXI Member ✭✭

    Ok, thanks for the reply.

    I tried to point out that I didn't use any Bird meters, just the Bird loads and the internal meter on the 6400M.

    The internal meter shows 1.3:1 when the internal meters of other rigs attached to the same loads show "flat". I'll just ignore it unless it gets worse or gets in my way for some other reason.

    73 Jim N7CXI

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