Tarheel on Travel Trailer

Discussion in 'On the Road' started by N1SFT, Jul 22, 2019.

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  1. N1SFT

    N1SFT XML Subscriber QRZ Page

    Hi fellow RVers.

    I'm fixin to install HF in the Travel Trailer for (obviously) fixed operation.

    The Tarheel seems to be as good a compromise as any, but I wanted to run my understanding across the hive;

    Installing the tilt-over base on the roof of the camper, so that while under way (being towed) the unit lays on the roof with proper supports, the base would be towards the front, and the coil/whip fold down towards the tail.

    The obvious question is regarding the RF Ground.

    The roof of the camper is roughly 9 feet above the twin I-beam chassis of the trailer. Running a ground strap from the chassis frame to the tilt-over base seems to be little value. So, if this were a VHF install, I'd proceed to construct some form of metal ground plane skin that would be adhered to the rubber roof membrane.

    VHF is easy at least conceptually.

    But I can't imagine an 8 foot wide by 8 foot long section of "groundplane roof" would make any difference at all for HF.

    So, for all the photos we see of RV's with a screwdriver on the roof - how are they RF Grounded? You're over 11 feet over the Earth ground, so little if any ground capacitance can occur.

    Tarheel instructions instruct the installer to make sure Vehicle Ground is within 12 inches of the base. Thats impossible to achieve on a fiberglass sided stick built RV camper.
    PED4ENKO likes this.
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    A long time ago, I installed 2-way radios (mostly CB) in vehicles. When I installed on top of a large non-conductive surface, I typically used aluminum tape to form a large "X" at the antenna location. Thin aluminum sheet/foil would also work. Use a good adhesive, such as Scotch 77 or 90.
  3. KB3WFV

    KB3WFV Premium Subscriber QRZ Page

    Hi Craig

    The Tareheel screwdriver antenna is great for using with an RV. Your right the ground plane is important and difficult to achieve on an RV. My rubber roof was damaged by a tree branch and required replacement. I was able to take advantage of this disaster and installed a layer of wire mesh under the entire length and width of the trailer before installing the new rubber roof.

    Here is a link to a QRZ post with a video about my install.

    I am not suggesting you tear up a perfectly good roof. However the ground plane needs to be directly below the antenna. You may try laying out several radials from the base in a star pattern on the roof. Use thin cooper wire 18ga mayve? The more the better. This can be installed when camping and removed while traveling. Or for a permanent installation on a EPDM rubber roof, you can glue down the radials by using a lap sealant or caulk like Dicor to cover the wires with. You could also use a roll of wire mesh to roll out on the roof while camping and roll it up when traveling. I don't see a way to permanently installing the mesh on top of the roof.

    In the thread linked above there are some photos from another Tarehel owner who mounted his on the A-frame of the hitch. This mounting provides a solid mount to the steel frame rail.

    The radial idea seems to be the least intrusive and easily implemented, while performing well as a ground plane for the antenna.

    Last edited: Jul 22, 2019
    K0UO likes this.
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    -Aluminum Duct Tape from hardware store. Tape pattern to roof, connect to antenna base.

    -Adhesive copper foil, Amazon, Ebay, electrical dealers. Ditto.

    -Removable wire radials that drape down from antenna and roof. Use alligator clips. "Silky" coated antenna wire from Wireman or dealers would be good.
    WA7PRC likes this.
  5. N1SFT

    N1SFT XML Subscriber QRZ Page

    Hi Brian, thanks for responding! Actually I did see your thread on the project previously, it basically planted the "seed" as it were. :)

    By putting the tarheel up on the roof with a constructed ground plane, that installation is basically an elevated-radial design, right?

    Based on ARRL "guidance" an elevated radial design needs 1/4 wave wires, usually (2) wires per band... so a 40m vertical should have 32ft+/- of radials.

    The reason for it being considered an "elevated radial" is because the counterpoise lines are not connected to the metal mass of the vehicle, and because the vertical height above Earth reduces the capacitance-coupling to near zero I would imagine.

    Unlike a metal-skinned RV, or a bus, or an over the road truck-tractor, the fiberglass RV with rubber roof just doesn't provide a ground path for RF.

    These are my thoughts, and I'm interested in differing opinions.

    My guess is on a 30 foot RV, a vertical antenna for 40m will be just OK, and at 80m that same antenna would perform even worse. But at 20m, I'm guessing it performs quite satisfactory.
  6. W5LZ

    W5LZ Ham Member QRZ Page

    Another option would be to add the 'radials/ground' at the antenna's feed point and running those radials/grounds down the corners of the trailer to ground level (not moving, right?). String them out as appropriate/convenient. You could make the lengths almost anything you wanted. What kind'a wire? Whatever you happen to have basically, as long as it's a conductor it won't matter. The radiation pattern may not be exactly what the 'classical' one is, but who cares, it'll work.
    N1SFT and KB3WFV like this.
  7. KB3WFV

    KB3WFV Premium Subscriber QRZ Page

    Hi Craig, I'm glad the post was inspiring and my apologies for being a bad influence. :)

    The counterpoise/ground plane doesn't have to run in a straight line. That 32 feet can zig-zag back and forth beneath the antenna reaming inside of a 25 foot space. Imagin all of the different paths RF can take on wire mesh.

    A couple of other things to consider. 1) The Tareheel is adjustable in vertical length which allows the best possible match using the available ground plane on a given frequency. 2) The steel frame of chassis will play a role in things as well.

    I do not recall how your trailer is constructed, but mine is aluminum frame with fiberglass sidewall on a steel frame and a plywood roof covered in EPDM rubber. Under the plywood is foil backed insulation. At the roof edge along the sides are 8 inch wide metal flashing strips that forms a rolled edge to the side wall along the entire length of the trailer. I installed wire mesh which fastens to the metal flashing which is fasten to the aluminum framing as it rolls over the edge. So in effect the wire mesh, aluminum framing and the steel chassis all work as a ground plane, at least that's my theory. All of the components have continuity to each other at DC.

    It's not perfect. Ideally there would be bonding straps across any point that there are welds in the aluminum frame or steel chassis and the wire mesh would be soldered to the flashing. Tareheel technical support actually recommended that the entire roof surface be covered entirely with 4x8 sheets of metal and that those sheets be bonded together for a ground plane. Opting for speed of installation, lower cost and less weight I went with the wire mesh.

    The trailer is 35 feet long and the antenna is centered as best as the roof structure would allow me to. It is a little to the drivers side and slightly forward. I am also not perfectly bonded. Despite these less than perfect conditions the antenna performs well.

    I can not find my test results at the moment, but the antenna will tune from 6 meter all the way to 80 meter. I do not have an antenna test range but it does seem to perform well. I regularly use this antenna as net control on 40 meters and can work the same stations that I do from home. Not scientific data but somewhat a comparison to a known performance. All in all in my opinion it works very well, the biggest problem I have is noisy receive from all of the other campers or the camp ground.

    I think I would try a temporary test set up before a permanent install. Maybe a hamstick on some sort of weighted mount. Maybe a magnet. Set it on the roof and roll out some wire or screen/mesh, connect the wire or mesh physically to the antenna mount and test how things tune and perform. The only difference between the hamstick and the Tareheel is the tareheel is multi banded and remotely tune able. Nonetheless the hamstick will give you a single band to play with and test the ground plane.

    - Brian
    N1SFT likes this.
  8. N1SFT

    N1SFT XML Subscriber QRZ Page

    Great points! Thanks for taking the time to respond. I will take these thoughts to heart as I build the station. (I'm still in the planning phase, not ready to pull any triggers yet.)
  9. N7ZAU

    N7ZAU Ham Member QRZ Page

    Have you considered something like a Delta Loop that doesn't require a ground plane? Several designs for different frequencies. One choice is using Crappy poles to elevate the wire. Can attach an easy mount to the ladder to attach when you get to your destination.
  10. W0NAR

    W0NAR Ham Member QRZ Page

    I use a push up mast with a rotatable multi-band dipole.
    Rotator on the bottom. Works great QRO too !!!

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