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Resonating coax

Discussion in 'CB and Export Equipment and Accessories' started by BOOTY MONSTER, Jan 23, 2012.

  1. i saw this posted on another forum . seems to be some fine CB BS to me , but i figgured id ask here to find out if theres any truth to it or not .

    "Resonating coax

    Take your mfj readings as close to the antenna as you can. Use as short of a jumper as possible and tune the ant. for lowest reflect and hopefully your R will be close to 50 and x as low as possible.
    Chose whatever type of coax you want to run, rg8 rg213 lmr400 what ever will handle the power you have with room to upgrade is Ideal. You want the perfect leingth of coax to run you stuff with only enough extra as you can using this meathod.



    Here is how you resignate your coax:
    Choose a leingth of about 6 feet longer than needed, I prefer 8 feet extra.
    Use a low power stock radio, a swr meter, a small and cheap dummy load rated for 50ohms and a coax t connector.
    Here is how you cut and measure the coax.
    Connect the radio, using whatever short leingth of coax you have with two ends on it, one end to the radio the other to the swr meter.
    Connect your t connector to the output or antenna section of the meter.
    One side of the t connect your dummy load
    Key and note the swr on the meter of the dummy load only. (very important)
    Now hook your longer than needed section of coax your going to use from your last box or main feed from your equipment to antenna.
    The other end of the coax DO NOT CONNECT TO ANYTHING.
    Key the radio and note the swr increase from when you just keyed on the dummy load.
    If your swr is much higher than trim 3 inches off at a time until you start getting close to a 2.1 swr.
    Now just cut a very small amount off at a time until your at an exact match with the dummyload.
    (If your dummy load showed a 1.5 dont keep trimming to lower the swr with both connected, this will creat an unbalanced load)
    What your doing is tuning the coax to match the SWR of your dummy load and will make it resginate at 27mhz just like the dummy load is.
    Lastly put a new end on your new resignated leingth of coax ( prefereably by soldering it on). Remove your dummy load and t connector and hook up your equipment."
     
    #1

  2. Rb30

    Rb30 43WR30

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    Sounds like he is making a tuning stub, the only prob I can see is that if he is leaving an open end of a 1/4 wave stub then it will act like a wave trap. I use this method to cure TVI. If he adjusted then shorted the other end then it would act like a tuning stub manipulating the impedance
     
    #2
  3. RatsoW8

    RatsoW8 Supporting Member

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    Do you trust someone who wants to show you how to "resignate your coax"? Hmmmmm?
     
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  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Sounds like bullshit to me. If ,as stated in the example, the match at the antenna was a perfect 50n ohms and no reactance then the length of cable would make no difference whatsoever in the SWR. Measure, cut, install. Simple.
     
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  5. W5LZ

    W5LZ Crotchety Old Bastard

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    I don't see the point. It isn't making the feed line 'resonant' that's important, make the antenna resonant! Then the length of the feed line doesn't make any difference.
    Use that coax that you want to tune between that radio and that dummy load and it'll show that it's a pretty good length already. If you need that coax for a particular purpose, A stub for instance, why do it?
    - 'Doc
     
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  6. Beetle

    Beetle Well-Known Member

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    If you're making 1/4 WL feedline transformers, the MFJ-259B analyzer does a fine job. A 2-element quad driven element has a feedpoint impedance right around 100 ohms. A quarter-wave of 75-ohm coax (I use RG-11) between the feedpoint and the main 50-ohm feedline will show a nice low SWR.

    But it doesn't "resignate" anything, nor even resonate anything. It transforms the impedance, period.
     
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  7. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    about the only part I agree with is: "...Lastly put a new end on your new resignated leingth of coax ( prefereably by soldering it on)..."

    resignated??????

    leingth?????

    prefereably???



    I spell Bull Chit
    </P>

    but soldering IS the way to go
     
    #7
  8. 6.0 Liter

    6.0 Liter Coax abuse???

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    What Beetle said.........the only thing they were successful in doing was making the swr meter read close to what the antenna read at the feed point. The only reason I would ever do it is if I was gonna run an inline meter and I wanted it to read close to what the analyzer read at the feedpoint. Depending on where you place the meter inline, you will have differant readings, but it doesn't change the resonance of the antenna at all, just sorta makes the coax invisible to the meter ya know. My 2 cents
     
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  9. 928bolo

    928bolo W9WDX Amateur Radio Club Member

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    The description sounds like he was attempting to build a coax stub filter but the stub stays inline using the T-connector. These are used in multi-multi contest stations to reduce harmonic interference.

    Here are a few links if you are interested.


    http://www.k1ttt.net/technote/k2trstub.html

    K1TTT Technical Reference
     
    #9
    Last edited: Jan 23, 2012
  10. wouldn't using a electrical half wave length of coax help the meter read more accurately ? does the method described offer any benefits over using E 1/2 WLs of coax ?
     
    #10
  11. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    NO and NO

    adding or subtracting coax will not affect the ACCURACY of any meter movement**Jump_im**
     
    #11
  12. W5LZ

    W5LZ Crotchety Old Bastard

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    An electrical 1/2 wave length of feed line has the characteristic of showing the impedance match at one end of it at the other end of it. That means that if there's such a length used, then you'll see the impedance match at the antenna as that at the transmitter end. So, keeping that in mind, then yes, it can help "un-fool" a typical SWR meter. That part is true for one, or any number of electrical 1/2 wave lengths of coax, -OR- any other type of feed line. It certainly isn't going to 'correct' any 'bad' match, but will show you what's there. Then YOU can do any correcting required.
    - 'Doc
     
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  13. oh well , i was finally linked to the thread by 5150 . rubicon express was the original author over at the 11 meter outlaws forum .

    &bull; Login

    RE's follow up post suprised me .

    "This meathod is not my Idea. My goldfinger (45 audio) taught me this. Between two of us we have seen first hand 6 mobiles increase thier effective signals by up to 3 S units just by doing this.
    I did this after running a 4 pill for months, made this adjustment in a few minutes and keyed to the exact same guy to his base and he saw me bump up from a 7 to a 9 S unit.
    This can also help resolve SOME TVI and RFI bleedover issues at basestations. It however doesnt seem to help as much in your TX as compaired to mobiles.
    If you do all the hard math to calculate out the Velocity factor of your coax at 27 mhz the numbers always match the leingths doing it this way as well."

    3 s-units more just by changing coax length a few inches to several feet ...
    whoda thunks such a thing was possible ??**Jump_im**<<More audio>>
     
    #13
  14. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    WOW,............... I wonder what woulda happened if he bothered to try to get the ANTENNA resonant on the freq he was using:blink:
     
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  15. well , cool breeze agreed with him so it must be true !
     
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