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2m/70cm antenna for my RV with a rubber roof (no ground plane)

Discussion in 'On the Road' started by KC9OO, Jul 18, 2017.

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  1. KC9OO

    KC9OO Ham Member QRZ Page

    I have a Fourwinds Class C mobile home with a rubber roof and fiberglass laminated sides. No metal nowhere. I'm currently using a 2m thru-the-glass antenna -- you know, a dummy load. I'm installing a 2m/70cm radio and thought I'd take the opportunity to upgrade the antenna. Any suggestions on what I should purchase?

    Thanks,
    Jon
    KC9OO
     
  2. KD0CAC

    KD0CAC Ham Member QRZ Page

  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    I have had good luck using a large cookie sheet and mag mount.

    A oil drip pan should work even better and cost about 8 dollars at Auto Zone.

    That might look funny on top of your RV tho.

    Have Fun.
     
  4. K5BBC

    K5BBC Ham Member QRZ Page

    On a fiberglass truck topper, I used copper ribbon to form a ground plane. 1/4 inch ribbon, 19 inches long, and about 12 radials. I used a metal switchbox cover for reinforcement, ran the copper ribbon under it and into the 3/4 inch hole that was drilled for the NMO stub. I covered all of that with RV roof seal. Installed the NMO stub and 1/4 wave VHF antenna. I use that position for the APRS tracker, and get a 1.4:1 match.

    just to see what would happen, I tried a 1/4 wave uhf antenna, but couldn't get a match. Same for a short dual band. Using a dual band that's 1/2 wave VHF and 5/8 over 5/8 at UHF yields 1.2:1 on VHF, 1.5:1 on UHF. That type of antenna may be a bit tall (36-40 in) on top of an RV, though I know several RVers who use it mounted to their rear ladder.
     
    K7WFM likes this.
  5. K7WFM

    K7WFM Ham Member QRZ Page

    A metal roof ladder will work. Higher the better.
    Do you have a metal luggage rack or bat wing TV antenna up there? If so, afix the antenna to it.
    Also, the AC unit drip pan is galvanized steel and that should work as well.
     
  6. KB3WFV

    KB3WFV Premium Subscriber QRZ Page

    Hi Jon

    Are you planning on using this antenna while in motion or while set up at camp ?

    If in motion the roof of the class c may be too high for any antenna to avoid being taken out by tree branches or low overhangs such as gas stations. For in motion perhaps mounting a larsen antenna on the hood or corner of the from bumper? If using it while set up to camp, a diamond x50 would be a good choice it's short and light weight easy to put up or put down.

    Might even be able to come up with a set up using the x50 that would attach to the ladder on the rear of the coach ( if you have one). IN motion it would be below the roof line and at camp it could be elevated above the roof .

    I would be surprised if Fourwinds framed their coach roof with wood. It might have metal framing for roof trusses and foil backed insulation. There just might be some metal somewhere. You can remove an inside roof vent trim and peak around. There might be wood as support for the vent screws but I bet there is metal in there somewhere.

    Of course you can take my route.... get a branch to punch a hole the roof of your RV. When you go to replace the rubber roof and the broken plywood, put down wire mesh and antenna mounts before the new rubber goes down.

    The branch route is an expensive way to go but very effective .... the new Tarheel 200HP kick butt on the roof of our 5th wheel. (pictures on my QRZ page)

    73
    Bran
    KB3WFV
     
  7. KC9OO

    KC9OO Ham Member QRZ Page

    Thanks for all the replies. To answer a few questions, I do want to use this mobile, I don't want to use the ladder and I don't want to mess with the roof any more then is absolutely necessary (like me, it's old). I'm not interested in building a single-band antenna because I want both 2m and 70 cm. I will go looking for metal, though I'm not sure about the aluminum framing being sufficient. The AC could be a possibility. And I definitely won't have a tree limb poke a hole in the roof.

    I believe a 1/2 wave antenna will work without a vehicle ground plane. Am I correct on this? And if so, are there any 1/2 wave 2m/70cm mobile antennas out there?

    Thanks again,

    Jon
    KC9OO
     
  8. KB3WFV

    KB3WFV Premium Subscriber QRZ Page

    Aww common Jon, It's sooo much fun. Besides insurance pays for it.

    I don't think a mobile anything will work without a ground plane, but I didn't stay at a holiday Inn last night either, so I'm not sure.

    If you don't want to use the ladder, then the only sure bet for metal on the rood is the bottom half of the A/C unit. YOu can use a bracket like this ......

    https://www.dxengineering.com/parts...N5RoOqxMDkBjQrpfJ1kpf28CZDYoKXvoaAsIrEALw_wcB

    ..... and bolt it to the A/C. I would remove the plastic top and have a look see inside before drilling any holes. You don't want to hit a refrigerant line or wires.

    Might even be able to mount this bracket on a front fender between the hood and the fender in one corner.

    You could use it with this antenna

    https://www.dxengineering.com/parts/lsn-nmo2-70b

    Larsen probably has the most mobile applications for antennas and mounts. They have years of experience with police/fire and ems service. There are others MFJ, Comet , Hustler, etc etc... just Google 2m/440 mobile antenna and let your mouse do the clicking.

    Brian
    KB3WFV
     
  9. KC9OO

    KC9OO Ham Member QRZ Page

    Brian,

    Thanks for the suggestions and links. I think this is the way I'm going to go. Just have to wait for it to stop raining so I can get up on the roof and check out the AC unit. Luckily, it's just rain and not wind storms knocking tree limbs through the roof.

    73 de KC9OO
     
  10. K5BBC

    K5BBC Ham Member QRZ Page

    Not that is 1/2 wave in both bands. The physics just won't work that way.
    As I described above, a 1/2 wave VHF 5/8 over 5/8 wave UHF dual band will work.
     

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