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Dummy Load

Discussion in 'CB and Export Equipment and Accessories' started by undertaker, Sep 16, 2018.

  1. undertaker

    undertaker Undertaker

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    Ok gents I just got a new dummy load from MFJ. Now can someone please explain to me how to use it. I want to check the dead key on some of my radios. Now I don't understand electronics like most do. My occupation does not require that...

    So Please help
    if you don't mind...…………...
    Bobby


     

  2. Robb

    Robb Yup

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    radio > jumper cable > watt meter > jumper cable > dummy load

    OR

    radio > jumper cable > amp > jumper cable > watt meter > jumper cable > dummy load

    Dead key AM; no modulation
    Amp on 'high'
    Set radio dead key so that you see no more than 1/4 of rated amp output
     
    #2 Robb, Sep 16, 2018
    Last edited: Sep 16, 2018
  3. 357magnum

    357magnum Well-Known Member

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    Bobby , Is this a trap again ?o_O:ROFLMAO::ROFLMAO: 73 and God Bless , Leo
     
  4. 357magnum

    357magnum Well-Known Member

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    Someone has to come up with a way to explain it , in Embalming Lingo , just a thought .;)
     
    undertaker likes this.
  5. undertaker

    undertaker Undertaker

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    Thanks Robb Exellent idea leo!!!!(y)(y)(y)(y)(y)(y)
     
    357magnum likes this.
  6. El Kabong

    El Kabong New Member

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    Has anyone else seen a dummy load that reads an SWR of 1.2:1? Mine does. It's an MFJ 1.5KW HF load.
     
  7. Robb

    Robb Yup

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    Did you check the resistance with a DVM yet?
     
    El Kabong, sunbulls and 357magnum like this.
  8. El Kabong

    El Kabong New Member

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    57.5 Ohms. It looks intact inside. Nothing bent, burnt or broken. Next step is to take it ALL apart.
     
  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    What model number? Is it an MFJ-264? If it is it is hardly what one would call a 1.5Kw load. I have one. I know.


    You won't find anything. The resistor has changed value. If it was ever over heated, even just once, it will shift in value and go high. If you ar 100% it was never run too hot then the answer lies in the manufacturer's name.......MFJ. The are know for cutting corners and may have purchased some "close enough" resistors. In any event 1.2:1 is perfectly fine.
     
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  10. sunbulls

    sunbulls Well-Known Member

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    I did a millisecond double take on that acronym when I realized my veterinarian is clueless about electronics.:rolleyes:
     
  11. El Kabong

    El Kabong New Member

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    Nope, I bought it used. It could have been run hot before. Crap, I needed a good reliable dummy load. Now I have a semi reliable dummy load, as long as I don't care about accurate SWR readings.

    Yup it's a 264. I was hoping it was a series of resistors in the ceramic tube, then I could find the weak one and replace it. Guess not huh?
     
  12. El Kabong

    El Kabong New Member

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    UPDATE: I just got this reply from MFJ. about my inaccurate Dummy Load. You're gonna love this one.

    "there is a plus/minus tolerance of 10% on both sides for the dummy load resistor." Alice M.


    So there it is. My load is not broken or even out of plumb. It's JUST FINE.
     
  13. nomadradio

    nomadradio Analog Retentive

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    Assuming the meter is within 2 percent, that reading is probably within the limits of the 10% spec.

    57.5 ohms would be 1.15 to 1 SWR.

    No biggie.

    73
     
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  14. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Nope. It is a single 50 I think.......or 100 watt ceramic resistor.

    10% is a typical tolerance and the load should measure between 45 and 55 ohms and show 1.1:1. I have started looking at ceramic chip resistors on a LARGE heatsink and have bought a pair of 100 ohm 800 watt chip resistors. I mounted each of them on their own heatsink mounted back to back and wired in parallel. Makes a NICE kilowatt dry load. More if I put a fan on it. IIRC I got the resistors from Florida RF on Ebay.
     
  15. w9cll

    w9cll W9WDX Amateur Radio Club Member

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    Yep use is and stop being a slave to the SWR meter.
     
    357magnum likes this.

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