Built-in 11m antenna - tuner for 2m/440

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD0UCA, Sep 3, 2017.

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  1. KD0UCA

    KD0UCA Ham Member QRZ Page

    Greetings! What happens at my job, is I drive commercial trucks that has a cb antenna built in. I'm not always in the same truck day to day. Even during mid-day, I may have to swap trucks.

    What I'd like is some advice on using an autotuner that can match the 11m antenna to 2m/440 so I can plug in and go.

    A mag mount on top of the cab isn't much of an option because the top of the cab isn't as high as the fiber glass cargo box behind me.

    These are 36 to 42 ft freightliner and kenworth straight box trucks I'm working with.

    Any suggestions?
     
  2. KB1CKT

    KB1CKT Ham Member QRZ Page

    Is the antenna already attached, and thus the one to use? I'm a bit dubious of matching an CB antenna to 2m let alone 440. Sounds like it is provided; can you touch the antenna, or would you get in trouble? I'm wondering if you can just unscrew it for the trip and replace with a better antenna. Even then, the coax may be dubious on 440.

    Sometimes what you have is what you have. If the antenna is "blocked" by the box then it's simply the way it is. "Blocked" is still higher up than using an HT in the cab. And of course, even an HT in the cab is higher up than most cars, and if it's a fiberglass box, then it's not too shielded. Then again, if it's a fiberglass cab, it's not much of an option either.

    Are you looking to keep 11m coverage, or only looking for 2m/440 coverage? If you need to keep 11m I'd be thinking of just carrying a 2m/440 magmount. Whatever is easiest to carry and swap around, given the amount of movement that has to undertake. But I'd get a cheap antenna as the coax is apt to wear out (pinched in the door or otherwise flexed often), maybe carry a spare, new in bag, for when it wears out.

    What kind of power are you running?
     
  3. KD0UCA

    KD0UCA Ham Member QRZ Page

    As described in my original post, magmount isn't much of an option for me. It would be a PIA to have to swap it around all the time... and I'll probably just end up too frustrated having to fiddle with it all the time. Although the box is fiberglass, the contents inside will vary.

    As far as power, I'm not planning on running much above 25 or so. The trucks are leased, any modification such as swapping out the antenna is a no-no. I won't be using 11m at all... and honestly, I can even do without 440.

    Pics included to help give the idea of what im working with. 20170903_071605.jpg 20170903_071642.jpg
     
  4. KA5IVR

    KA5IVR Subscriber QRZ Page

    IMO, trying to tune that 11m antenna to be resonant will not work too well and just be a PITA.

    I would try the 2/440 Mag Mount first and see how that works, if the cab is metal. I don't think the fiberglass box on the back will make too much of a difference. Another idea, depending what style mirrors are on those trucks, use a clip-on mirror mount.
     
  5. KD0UCA

    KD0UCA Ham Member QRZ Page

    Maybe I'm missing something here... I notice for HF, you can string up practically any length of wire, and the tuner can match it. Do such devices just not exist for the shorter wave of UHF/vhf?
     
  6. M0GVZ

    M0GVZ Ham Member QRZ Page

    Use a magmount on the middle of the roof or if you can get to the back of the CB make up a male to female lead to screw on the end of the coax going to the CB and use a 1/4 wave 2m whip with a 3/8 thread on it. The length of that CB antenna is so much that even if you can find an ATU to use the majority of your signal will be heading towards the sky.
     
  7. M0GVZ

    M0GVZ Ham Member QRZ Page

    They do but they're more expensive and usually pointless as the main reason people use them on HF is because it allows you to use a shorter length of wire as an antenna due to lack of room which is not a problem for VHF/UHF.
     
  8. KC3RN

    KC3RN Ham Member QRZ Page

    As far as I'm aware, there are no auto tuners available that will tune 2m or 440, and a manual tuner would be more of a PITA than a small mag mount......
     
  9. KD0UCA

    KD0UCA Ham Member QRZ Page

    M0GVT... Thank you very much for that explanation! It answers a lot of my confusion!
     
  10. KG7SWP

    KG7SWP Ham Member QRZ Page

    For VHF get an old CB fiberglass whip. Strip the outer plastic sheath. Cut length to about 20"(With wire unwrapped). Trim wire to resonance, using a VHF SWR meter. You may need a matching coil that can be clipped on for 440 Mhz. If you know someone with a VHF/UHF antenna analyzer, it will go much quicker.
    It will work, but not as good as something mounted on top of the box (Which I think is aluminum).
    The reason for VHF/UHF tuners not being a common unit (70s & 80s had a few options), is that stray capacitance & inductance (4" of wire length is a large thing at 440Mhz.) affect the system.

    Ed
     

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