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Coax loss

Discussion in 'General Ham Radio Discussion' started by KD2GOE, May 25, 2019.

  1. KD2GOE

    KD2GOE W9WDX Amateur Radio Club Member

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    Well I did a power test on 446mhz on 50'..
    Testing at the radio I got 23watts
    Testing at the other end I get 13w
    I am loosing 10w through coax loss....
    Is this excessive or something normal?

    This is the coax
    http://www.davisrf.com/buryflex.php


     
    #1 KD2GOE, May 25, 2019
    Last edited: May 26, 2019

  2. sp5it

    sp5it Master of puppets

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    Your meter is fooling you.
     
  3. KD2GOE

    KD2GOE W9WDX Amateur Radio Club Member

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    How so??
     
  4. sp5it

    sp5it Master of puppets

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    Shadetree Mechanic likes this.
  5. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Thanks for the link, I often find myself thinking about RF power transmission.
     
  6. KC9Q

    KC9Q Supporting Member

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    GOE,

    23 Watts = +43.6173 dBm
    Connector Loss = -0.1 dB
    50 ft BuryFlex = -1.4 dB
    Connector Loss = -0.1 dB

    Total Gain = 43.6173 dBm
    Total Loss = -1.6 dB

    ERP = 43.6173 – 1.6 = 42.0173 dBm
    = 15.9121 Watts

    13 Watts / 15.9121 Watts = 0.816988
    100 x .816988 = 81.6988 %
    100% – 81.6988% = 18.3012% (~18.3%)

    You're measuring 13 Watts which is about a 18.3% higher loss than what should be.
    Either your transmission line assembly has more loss than expected, or there is
    a 18.3% error introduced by the meter, or a combination of the two.

    Mike
     
    Tallman, sp5it and Shadetree Mechanic like this.
  7. KD2GOE

    KD2GOE W9WDX Amateur Radio Club Member

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    ok so you would be expecting a reading of 15w out the other end?

    Well my meter is a MFJ-847 seems right or close with my TS-2000 and with 3 HT's that are ratted at 4w
    The radio being tested is a 25w Kenwood TK-840 i have 4 of them and they read 23~25W

    it maybe a compound of the 2.
    all tests where preformed with a dummy load..
     
  8. KD2GOE

    KD2GOE W9WDX Amateur Radio Club Member

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    I put LMR400 in and 23w in and it is saying 12.2 out... :unsure:


    [​IMG]
     
  9. sp5it

    sp5it Master of puppets

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    Your antenna have R=250 Ohm? Does not have 50 either, but should be close.
     
    #9 sp5it, May 26, 2019
    Last edited: May 26, 2019
  10. KD2GOE

    KD2GOE W9WDX Amateur Radio Club Member

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    ahhhh yeah i don't know how to use this program..


    well my Friend has a bird meter he is going to swing by and we will test with that...
     
  11. sp5it

    sp5it Master of puppets

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    Use dummy load instead of antenna. You should see coax loss.
    Mike
     
  12. 543_Dallas

    543_Dallas Sr. Member

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    According to this calculator

    https://www.qsl.net/co8tw/Coax_Calculator.htm

    you're about 3 watts off. That's good enough. You have to be using a dummy load for accurate readings. When I tested the lmr400 to my vhf/uhf antenna with a bird 43 I found this calculator to be very close.
     
    Shadetree Mechanic likes this.
  13. Road Squawker

    Road Squawker Sr. Member

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    A little "secret" that the coax companies don't (actively) tell you is the Db loss/100 feet is into a 50 ohm load.
     
    #13 Road Squawker, May 26, 2019
    Last edited: May 26, 2019
  14. SIX-SHOOTER

    SIX-SHOOTER Sr. Member

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    Well within the accuracy of most wattmeters with that reading. Even within the Bird meters accuracy.

    SIX-SHOOTER
     
  15. KD2GOE

    KD2GOE W9WDX Amateur Radio Club Member

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    I don't think I was clear enough I was using a dummy load not the antenna
    I did that...
     
    #15 KD2GOE, May 26, 2019
    Last edited: May 26, 2019
    Marconi likes this.

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