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Mobile antenna shafts

Discussion in 'CB Antennas' started by phantom309, Aug 2, 2016.

  1. phantom309

    phantom309 Active Member

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    The Wilson trucker version has a 5 or 10 inch shaft and my Sirio performer has an 8 inch shaft.

    But I am trying to find a 17-24 inch shaft.



    I don't know weather I am calling it the wrong name or weather 10 inch is the biggest you can buy.

    Want to mount the antenna in the stake hole in the bed of my pickup truck but have the coil at or above roof height. But do not want to drill though the roof, and getting ready to lay out 7,000 on a paint job so really don't want to use a mag mount.
     

  2. M0GVZ

    M0GVZ Sr. Member

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    Doesn't work like that if you're planning to try to move the "base" of the antenna higher. The whole of the antenna transmits including the shaft below the coil. The shafts are a specific designed length and altering them alters the tuning of the antenna. As the coil is designed to work with a specific length its not just a case of lopping more off the whip.
     
  3. Needle Bender

    Needle Bender ...he thinks it's funny that I stepped in it

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    I both agree & disagree.

    I've done just what he said and had great luck, however, as you imply, certain coils tend to prefer a certain height above the sheet metal.

    I'd give it a try, and yes they do make 18" shafts - and longer. Hustler makes a 54" folding shaft.
    A friend had a Wilson 5K trucker on a 6" shaft on the roof of a Camry and tried out his 18" shaft.
    - He had to shorten the whip about 1/2 - 1/3 the additional length of the shaft but it now performs better, at 30 miles he begins to fade where he used to get to only 25 or so miles when I'd start to lose his signal.
     
    2NC995, rabbiporkchop and 543_Dallas like this.
  4. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    Do a Google search on these 22 inch masts.

    Hustler HF Mobile Antenna Masts MO-4
     
  5. rabbiporkchop

    rabbiporkchop Sr. Member

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    If you have a machine shop make you a tool like this one you can make your own shafts and experiment with different lengths.
    [​IMG]
    [​IMG]
     
  6. 2ndstring

    2ndstring New Member

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    Old thread, I know... but here goes anyway. I am running a browning coil antenna on my Cascadia using a 16" shaft. Going by the digital display on the radio my swr's were running around 1.5 - 1.7. I added a grounding strap from the plate of the mirror mount to a bracket attached to the frame. For a day or so the swr reading dropped to 1.2 - 1.4, occasionally 1.0 on ssb. The readings have crept back up to original or a point or two higher. (Don't know why, I checked and all looks like I installed it) I am considering using a longer shaft 22" or 36" or moving to a perch over the passenger door where there is more fiberglass and less metal. The latter may eliminate the shaft altogether. How will a longer shaft or no shaft relate to the stinger length?
     
  7. Recon

    Recon NY 881

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    A Predator 10K is available with a 22" and 27" shaft. With the combination of a Breedlove Stake Pocket Mount with the Quick Disconnect device and the 22" shaft, the 22" shaft will clear the top of the cab by only one-inch. I recommend to go with the 27" shaft.
     
  8. Recon

    Recon NY 881

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    I recommend you read the posts relating to; Help With Monkey Made Antenna , before you dive-in buying a longer shaft for the stake pocket.
     
  9. Recon

    Recon NY 881

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    Have you seen the Larson Third Brake Light Antenna Mount or the Bullet Proof Diesel Third Brake Light Antenna Mount?
     
  10. Slowmover

    Slowmover Sr. Member

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    Antenna mounted where?

    In a new model 2018 Cascadia my best results were with the new PRO COMM adjustable mirror mounts and a pair of 7’ Skipshooters. (If I could hear them, they could hear me).

    Top load antennas have worked best for me in co-phase arrangements. New RG8 coax to bypass factory cable.

    “Craig Sez” over on Truckers Report has a long shaft with a 102” on it. An avid enthusiast.

    As to shaft length: More Below = Less Above.

    A decent SWR meter is basic, and you are best off with someone who has an antenna analyzer.

    A DC ground can help, but it’s more of an RF problem (both called grounds or bonds).

    Instalk RF bonds (tinned copper brand 1.0”w) across both door hinges with #10 self drill and star washer underneath (both sides of truck). Keep them 10” or less ideally. Shortest is Bestest.

    While testing have doors closed. Ck with engine on and off.

    .
     
  11. 2NC995

    2NC995 DAN

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    I always figured the idea behind a longer shaft was to prevent interaction between the coil and the body/sheet metal. It’s a given that lengthening the bottom will require shortening the top, and understandable the bottom still radiates.
     
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  12. 2NC995

    2NC995 DAN

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    I played around with this idea some more using loaded qtr wave calculators. I was surprised to see how much the required inductance changed as the coil was moved up the antenna. Basically, the higher you go the more inductance is needed to maintain the same length. By the the time you get to a top loaded antenna, you need much more inductance than with a base loaded antenna.

    Alternatively, moving the SAME coil up the antenna results in a longer OAL.

    It’s be interesting to see, all things with construction and mounting location being equal (that’s a big factor, IMO) how much difference exists between base, center and top loading. I suspect the differences may be much smaller than is sometimes speculated.

    Throw mounting location into the mix by putting the antenna in a stake hole behind a pickup cab or on an 18 wheeler mirror and I think coil location would be a much larger factor.
     
    Slowmover likes this.
  13. Slowmover

    Slowmover Sr. Member

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    When the coils on, say, a Wilson 2000 can “see” each other (Pete or KW large car) they work well.

    Ok a typical aero company truck, they don’t do either. Not without a shaft below. Stuck next to body versus being in clear air. (Tried it).

    IMO, I’ll take top load SKIPSHOOTERS in that situation every time.
    6’ or 7’ can work. (Better than other brands in these lengths).

    Having antenna(s) that will work, survive, and not be attractive to thieves is priority over last dB.

    Someone with more time and has expertise can likely do more, not just explain better.

    Base-Load on a metal roof would be an ideal. It’s rare unless one is pulling a trailer not much different in height. In most of those cases, drivers mount an antenna on a rear grab bar allowing a coil to be up and above.

    On the Great Plains is where one runs into enough tankers, cattle haulers and flatbeds running large cars (with loud radios) — many of them familiar with each other over a region 300 x 300 miles — that metal-body truck performance is the real advantage versus location or type.

    That the airwaves are less crowded is also a real help.
    Radios, or interference.

    A “problem” is that some of these guys transmit much, MUCH farther than they can hear. Those cabs are loud. And audio reproduction poor (built-in speaker or that crappy chrome Wilson piece).

    .
     
    walterjn and 2NC995 like this.
  14. 2NC995

    2NC995 DAN

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    Thanks. A lot of my assumptions are based on thoughts like this. Don’t know if they’re true or not, but anecdotal information suggests that having the coil above body metal counts for a lot.
     
    Slowmover likes this.
  15. Slowmover

    Slowmover Sr. Member

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    The second crowd with good radios are the wind-millers. Have to be able to communicate with escort/pilot cars. Some have two-three radios set to different channels.

    But, as they’re busy, one doesn’t involve them in non-work related chatter. (Same for other heavy haul for Oilfield, etc).

    I’ve been reading on RAMI antennas (RA Miller: Defense Avionics) as next tractor so equipped. Handles CB/AM-FM/Cell off an antenna pair. Duplexer in dash. Multiple lengths of coax. There are a few videos by the company for those interested (“Volvo Antenna Trouble Shooting; @ 10” long). Antennas at mirror ends.

    Drivers tend to bypass with a “bird perch” mount on an antenna base screw. Own coax. Now the antenna is literally against the body.

    Freighliner not terribly different to solution. .

    Have to get them high.

    A “rule of thumb” is 2/3 of each antenna can see each other in a co-phase setup. (Is it accurate? Well, one needs to tilt forward from 5-20/degrees to accomplish it, often. IIRC, distance is 85” or so).

    Help with an analyzer is maybe a handful of shops from Rockies eastward I’ve heard of. Had a guy outside of town here “help” me with a BUSTED 259 (ha!). Told him I’d pay for other work, but not that portion.

    With a CB shop in good repute it’s an installer with years of success with a particular truck model that pays off. As in, it may not be great, BUT IT WORKS!!

    .
     
    #15 Slowmover, Jan 10, 2020
    Last edited: Jan 10, 2020

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