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1.2KW RF Detector Impedance?

Discussion in 'Radio and Wireless' started by RHeTTRoNiCS, Apr 22, 2013.

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  1. RHeTTRoNiCS

    RHeTTRoNiCS

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    Mar 28, 2013
    Hello All…any idea how much should be the impedance of the line can be read by multimeter when using to detect a 1.2KW RF?
     
    Last edited: Apr 22, 2013
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Do not do it.

    If you do not know what you are doing, you are putting yourself into extreme danger.

    You have not given details on the equipment or your capability.
     
  3. davenn

    davenn Moderator

    13,671
    1,892
    Sep 5, 2009
    Any transmitter under test should be put into a dummy load....

    1) of an impedance that the transmitter is designed to fed into.... commonly 50 Ohms

    2) The dummy load and power meter ( NOT A MULTI METER) should be rated to handle at least the max power of the transmitter and preferably more to give "headroom" so that the test equip isnt damaged.

    You should NOT be playing with 1200W transmitters unless you completely .....
    1) understand these facts
    2) have the appropriate test equipment

    Dave
     
  4. RHeTTRoNiCS

    RHeTTRoNiCS

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    Mar 28, 2013
    Thanks guys for the tips....i am t-shooting the unit off power....actually the unit is ok when we installed and power-up onto the system. But when we fire the RF about 1000Watts, the unit will shut-off...Confirmed the unit is faulty coz when we replaced it the system works just fine....Now am checking the faulty unit, i found detector diode impedance is 300ohms...this detector diode is connected into the waveguide at output area...am not sure if impedance is normal, or bad....Any idea? thanks a lot.
     
  5. davenn

    davenn Moderator

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    1,892
    Sep 5, 2009
    what is the diode and what freq is the transmitter ?
     
  6. RHeTTRoNiCS

    RHeTTRoNiCS

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    Mar 28, 2013
    A diode detector and the unit am t-shooting is RF Generator (Part Number 912419). The diode detector (a schottky) is connected to the waveguide output and then with bnc connector. When i measure the bnc impedance, it read 300ohms....again, i suspected the impedance is not right to detect such high power upto 2.5Ghz....but need further confirmation from expert (u guys). Becuase this diode detector is quite expensive. Thanks.
     
    Last edited: Apr 23, 2013
  7. RHeTTRoNiCS

    RHeTTRoNiCS

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    Mar 28, 2013
    Let me simplify my question...What should be the appropriate impedance of bnc when that line is going to use to detect RF power upto 2.5GHz...Is it 300 ohms is ok? Or need higher/lower? Thanks...
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    The general answer is "a matching impedance".

    I don't know what the impedance of the line is that you're connecting it to.

    If you're measuring power you'll need a 1200W dummy load. For 2.5GHz that's going to be a pretty specialised part.

    Personally I wouldn't want to be in the same room as such a device. (actually I am -- it's called a microwave oven -- but it has interlocks and shielding to protect me)
     
  9. RHeTTRoNiCS

    RHeTTRoNiCS

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    Mar 28, 2013
    So in short...the 300ohms can be correct to use for 2.5GHz, as long as no issue on impedance matching? Thus, i am wrong to say that the higher the RF power the higher impedance is required....and should be matter with matching impedance?...Thanks..
     
  10. davenn

    davenn Moderator

    13,671
    1,892
    Sep 5, 2009
    You are getting seriously sidetracked. Understand that the diode is only sampling the RF. Its impedance is irrelevent as far as the overall RF circuit goes.

    The transmitter wants to see the appropriate impedance of the feedline and the antenna or dummy load on the end of the line. Variations in the diode are not going to affect that. The only thing that diode variations are going to affect is the amount of sampled voltage that is generated for your measuring circuit.

    So you MUST make sure that the WAVEGUIDE IS be terminated correctly.
    1) The termination MUST be able to handle the level of power you are going to put into it
    2) The termination MUST be of an impedance value that the transmitter expects to see on the end of the waveguide


    Dave
     
    Last edited: Apr 25, 2013
  11. RHeTTRoNiCS

    RHeTTRoNiCS

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    0
    Mar 28, 2013
    Thanks davenn...helping me out from wrong direction....
     
    Last edited: Apr 25, 2013
  12. RHeTTRoNiCS

    RHeTTRoNiCS

    35
    0
    Mar 28, 2013


    Thanks davenn...helping me out from wrong direction....by the way, i just asked the technician to measure the impedance of diode detector from the good unit (same model i am t-shooting) and he said it read 1.8K ohms...but though they have same unit their detector diode is came from different manufacturer...The good unit have part number DM212 (from S-Team) in which the bad unit have part number 060101 (from AGL). Now i am confuse again why this both same unit is using different diode detector and also have different impedance....the reason i suspect the 300 ohms is bad impedance because 1.8K impedance is running good...thanks.
     
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