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Thread: RF in 2017 GMC 2500HD

  1. #1

    Default RF in 2017 GMC 2500HD

    I have installed an IC-706MKIIG with a Little Tarheel II Antenna in my 2017 GMC Crew Cab 2500HD.

    The radio is installed under the back seat with a RedARC Battery Charger for the Aux battery because of the GMC smart charging system, and Voltage Boosters to keep the voltage at 13.6 VDC for the Radio. All power for the radios comes directly from the Aux Battery. The RedARC 25 amp charger charges the Aux battery off the Starting Battery.

    I have grounded the Bed of the truck at all four corners to the frame using flat strap. the Exhaust us grounded at the back and in front of the Cadillac converter using flat strap to the frame. The Cab is ground to the bed and the Frame using flat strap on both sides. The tailgate is grounded using flat strap on both sides. The hood is grounded on both sides using flat strap. I am so desperate I grounded the housing of the computer under the hood to the frame using flat strap. I have tried grounding the Pl 259 connector directly to the frame but took that back off when it didn't work.

    I have the RF choke back next to the antenna for the Tar Heel and also put one on the feed line for the Coax as suggested on http://k0bg.com/common.html .

    I have tried putting torriods on the power wires next to the charging battery and the Aux power lines. even though K0BG says that hardly helps but I am desperate to cure this problem. I'll try just about anything except driving off a high bridge, which might cure my frustration LOL. I have put various mix split bead torroids, 3/4" and 1" on various factory cables all through the truck trying to find where the RF is feeding into the truck without any luck.

    After a suggestion from a fellow ham. I placed a dummy load at the antenna mount and transmitted at full power and there was no RF in the truck controls. So I now know that the DC power and wiring and RF through the coax to the actual antenna are not the problem.

    I have tried mounting the antenna on the hood, on the bed as it is now, and up higher on the bed. All with the same result. The Mount is the fire stick swivle mount with the Tar Heel mount hardware installed on it. A second swivle mount offers support. I have tried the install with and without the support hardware with the same RF problem. Pictures attached (I Think)

    The feed line was RG-8X and is now 400max (LMR400 Flex) and is run out the vent on the back of the cab and runs back to the mount on the side with no factory harnesses.

    When I key up on 40 meters on even low power the warning lights on the dash immediately turn on; also on random 20 meter freqs. 80 meters seems to be okay. Its the SDS (Skid control) warning, the Brake warning light, and the Trailer Brake system warning lights. The Cruise control will disengage and stop working and the throttle kicks a bit but that might be the cruise control disengaging.

    After the Dummy load test I am sure the RF is feeding out through the antenna as it should, but it is feeding right back into the truck control system somewhere. BTW I have disengaged the ON Star antenna in the headliner and it is still disengaged. I even took the AM/FM antenna off and still the RF is in the truck.

    Somebody, who must be a genius, please HELP me, LOL.

    I have run out of ideas.

    Walter, W9KJO
    Attached Images Attached Images

  2. #2

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    Whats up with the second bracket? All the other pictures online show the antenna without the added support. That appears to be a metal bracket insulated with electrical tape and zip tied to the antenna. That screwdriver housing is actually part of the radiating element, in fact, its the portion that carries the most RF power. Get rid of that extra bracket. Also, im very curious to know whats wrapped around the coax at the bottom of the picture. I hope that isnt the power leads for the antenna motor...

  3. #3

    Default

    Quote Originally Posted by brandon lind View Post
    Whats up with the second bracket? All the other pictures online show the antenna without the added support. That appears to be a metal bracket insulated with electrical tape and zip tied to the antenna. That screwdriver housing is actually part of the radiating element, in fact, its the portion that carries the most RF power. Get rid of that extra bracket. Also, im very curious to know whats wrapped around the coax at the bottom of the picture. I hope that isnt the power leads for the antenna motor...
    The top bracket is support. I thought the same and raised the antenna up to the top bracket without a support and the RF was the same. The antenna feel very flimsy without some kind of support. The support has a piece of thick white plastic (for lack of the actual description of the stuff), with a piece of thick silicon gasket material to act as an insulator. I purchased a TarHeel actual mount and it has stainless steel that wraps around to give support to the antenna with nothing more than a kind of rubber grommet as an insulator. It would fall at about the same point on the antenna. https://www.tarheelantennas.com/mounts it is the LTMT1 mount. The actual antenna mount on the swivel mount is the mount off the LTMT1.

    Either way I did try it without the support mount and also raised it up to the top mount with the same result.

    I did not use the LTMT1 because it covers up to much of the tail light of the truck.

    The coax is inside plastic split flex to just help protect the coax and control wires from the elements and road stuff. Its just plastic, no metallic qualities at all.

    Thanks for your response.

    73, Walter

  4. #4
    gnuuser's Avatar
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    if you are running a lot of power its feeding back from someplace.
    many sensor systems in newer cars are isolated grounding due to sensitivity to electrical noise. therefore it may be inducing error signals in these wires.
    to be sure its a pain in the arse to track down.
    we had a similar issue with my fathers old police radio (it output 150 watts on transmit)
    how we solved that issue was to run the coax through oiltite flexible metal conduit
    similar to this
    https://www.walmart.com/ip/Southwire...duit/501554651

    cover entire length of coax and bond one end only to the negative battery terminal (do not bond other end to body)
    this may solve it but it depends on how much power your transmitting.

    and your control wires should not be near the coax separate them by at least a foot. (transmitting may induce current on the control wires and backfeed the power system)
    Last edited by gnuuser; Mon 24th Aug 2020 at 02:17.
    too much blood in my caffeine system.

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