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Mobile High swr !!!. Need a 27mhz ground independent antenna

Discussion in 'CB Antennas' started by johnxb351, Nov 24, 2020.

  1. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Sounds like a plan.

    Just take a wild guess at how tall the coil was.


     
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  2. johnxb351

    johnxb351 Member

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    MARCONI i never seen the coil only just read the specs. transformer wire 22 gauge times 21 times on 1/4'' dowel now it was a usa site so i gather that it's usa gauge wire and i did look up usa wire gauge and there is more than 1 gauge system . so in the end i turned 21 turns what i though my be that size wire just a guess on a 1/4 pipe it was 2.5 inch coil messument . you might have a better idear what wire with he used
     
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  3. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    So, you have no idea how tall the coil was?

    How about posting the link to your idea.
     
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  4. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    That's not a ground plane. Notice the "hot"side of the antenna is connected to it making more like a bottom mounted capacity hat. A cap hat needs to be on top of the antenna, hence the name cap hat.
     
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  5. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    That's a shunt coil connected between hot side of antenna to ground used for matching the impedance at the antennas feedpoint. A non coiled mobile antenna like a 102" whip may benefit from this for better matching.

    I make my own using enameled wire wrap 7 turns around the threads of a half inch diameter bolt.

    The OP still needs a good D.C. ground. If he's using a coiled/shortened whip antenna, he shouldn't need to do this.
     
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  6. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    Duplicate, no delete button anymore?
     
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  7. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    See link for the valuable details on the idea of NGP antennas and their special and unique coax.

    Link. http://www.firestik.com/CatalogFrame.htm


    No-Ground-Plane System
    COAXIAL CABLE ASSEMBLY

    [​IMG]

    Model K-8NGP: 17ft (5.2m) $44.99 (MSRP*)

    *MSRP (Manufactures Suggested Retail Price) in U.S. Dollars

    The K-8NGP is a tuned coaxial cable assembly that can only be used with special no-ground-plane antennas. This coaxial cable will not work with any standard ground plane dependent CB antenna. We offer it for replacement purposes (in the case of a damaged cable assembly from one of our no-ground-plane kits) or, for those who may be making an NGP kit while using a mount not found in one of our NGP kits. There are four primary components to a NGP antenna system ... the NGP antenna, the NGP coaxial cable assembly, the stud mount and the primary mount. The first three items are mandatory. As long as the primary mount has a 1/2-inch (25mm) hole to accept the stud mount, it will suffice.

    Because the K-8NGP coax contains a tuned circuit, reducing the length of the cable by as little as 1/4-inch (5mm) could render it useless. While there are some cases where the installation may dictate a small reduction in the length of the cable, this must be done carefully and with a degree of knowledge as to what effects on the resonant frequency that reducing the length will have on the assembly. There is an article posted in our tech help section regarding this procedure. Click here to read it.

    The NGP systems ONLY use the center lead of the coax to feed the antenna. The shield side of the coax is used to form the counterpoise (ground plane) that all transmitting antennas require. Many cables have been ruined by those unfamiliar with NGP systems. They think we made a mistake building the cable assembly so they reprocess the end and render it useless. We recommend that the ring terminal be soldered on instead of crimped (allows easy removal in case that need ever occurs).
    • Stranded center conductor to maximize flexibility and prevent untimely breakage.
    • 100% foil shielding to eliminate leakage.
    • 95% braided copper shielding over the foil for double protection.
    • Polyvinyl center insulation for ruggedness and longevity.
    • Performance that exceeds any similar product.
    To the novice, one of our NGP antennas may look the same as a standard GP antenna. But, the are never the same. All fiberglass NGP antennas leave the factory with a yellow band near the base. They can also be identified by the length of the close-wound section of the antenna at it's upper end. A table to help differentiate a GP product from an NGP product, based on loading coil length, is posted on our website. Click Here

    WHERE TO BUY?

    Visit our technical library to find the answers to the most common questions or to learn how to troubleshoot or even tune your CB antenna. It is unique on the Internet!

    1 Year Warranty
     
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  8. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Anybody notice how this coax could be different?
     
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  9. TheRATT

    TheRATT KJ7GKX

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    Do you have any links to specifics? I have a "fiberglass body" and trying to distill some things. Primarily, if the frame of my car is aluminum and other metals, does this give me any hope compared to the steel in a vehicle's body?

    And, as an exercise, how much steel do I need? If I just replaced the hood or fenders with steel ones - for instance - what is "enough"? Or is it never enough?

    When I vice grip my 102" to a shipping container, for instance, if that container was covered in fiberglass, how would that change the dynamics? I.E. would the steel underneath be "enough" or does it have to be the "outside" of the said antenna mount?
     
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  10. Crawdad

    Crawdad Well-Known Member

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    We must need an App for basic antenna theory nowadays
     
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  11. Crawdad

    Crawdad Well-Known Member

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    Ratt,
    A great source of info on mobile installs is the website of a well known amateur K0BG.
    www.k0bg.com

    73
     
  12. TheRATT

    TheRATT KJ7GKX

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    I've been there! And it is good stuff - I've been wanting to put a mobile rig in my Corvette (10/11m) but the complexity of trying to understand a way to make it work has kept me from doing anything serious.
     
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  13. Slowmover

    Slowmover Elmer

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    A picture somewhere of an all-tube GIGANTO-sized radio in a 1962 Vette. Behind pax seat.

    .
     
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  14. nomadradio

    nomadradio Analog Retentive

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    The so-called "no ground" antennas are in fact end-fed half wave antennas.

    All of them I have seen, anyway. The coax length is critical, since it serves as a matching transformer, stepping up the 50 ohm radio to the high impedance of a half-wave antenna element.

    Only the center wire of the coax connects to the antenna. The shield is connected only at the radio end. You'll find it best to ground the radio's metal case if you can. Otherwise the radio and coax will become antenna elements.

    Obtaining a proper ground plane or a proper substitute for it in a vehicle just gets trickier every year that goes by.

    The harder it gets to obtain a decent antenna ground, the more folks wish for an antenna independent of that requirement.

    As the old saying goes, "Wish in one hand......."

    73
     
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  15. M0GVZ

    M0GVZ Sr. Member

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    They've basically done exactly what I said in my earlier post, deliberately design the coax to be used as a RF ground, the main difference being no connection to the ground side of the mount and using a half wavelength so they don't have the cost of using a RF choke although personally I would still do so.

    Look at the unterminated end. You'll notice that the outer braid is completely stripped back and that there's only one crimp on connector for use with the centre conductor so it makes no contact with the antenna mount when you install it. Also it's a very specific length and it states no cutting.

    It's effectively trying to re-create a T2LT type antenna using the antenna you bought and screwed into the mount as the radiating element instead of a length of stripped back coax.
     

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