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eHam Forums => Mobile Ham => Topic started by: NT6U on September 17, 2016, 04:40:00 AM



Title: Fiberglass Camper Shells & Antennas
Post by: NT6U on September 17, 2016, 04:40:00 AM
I am installing a new fiberglass Snug Top shell along with my new HF & VHF mobile install (Earlier thread 480 HX install by NT6U).
      Would it be worth the money to line the interior of the bottom inside of the shell with a copper mesh or strapping (Georgia Copper) or would a simple 20ga. flat strap galvanized sheet metal serve the same purpose as a electrical counterpoise?

     I intend to electrically bond this strapping @ all 4 corners to the frame with copper strapping.  I also intend to drill through the fiberglass roof for my antenna mounting, of course adding structural metal to support an antenna.  I also intend on RE-fiber glassing over the added metals to keep them secure, before I reinstall the camper shell carpet.
I will be "hiding" all the work with carpet when I'm done so I don't care what it looks like between the glass shell and carpet.

Does anyone have any other suggestions? Wire as radials ect?  Am I overthinking this?
Thank you.


Title: RE: Fiberglass Camper Shells & Antennas
Post by: KG4RUL on September 17, 2016, 05:38:51 AM
Consider that a normal car body is made from sheet steel not copper.  So, since you have to add metal for structure anyway, use it for a ground-plane.


Title: RE: Fiberglass Camper Shells & Antennas
Post by: AI7PM on September 18, 2016, 01:43:51 PM
I tried this for VHF/UHF. Sheet metal, either top, and/or on the bottom of the topper didn't workout for 1/4 or 1/2 wave on UHF. I tried everything I could come up with. Grounds, and not, in every way you could think of. The Comet NR770 dual band would match. It's 5/8 over 5/8 on UHF. That gave me 1.4:1 It's 1'2 wave on VHF, and was 1:1.

On VHF I could get a good match on 1/4 and 1/2 wave antennas.

A bird strike (LARGE bird) cleaned both of them right off of the topper, so I just added two more NMOs to the cab roof and went back to commercial grade antennas with springs.

I kept one position on the topper. I removed the sheet metal, and installed copper ribbon radials, then repaird and sealed the roof. Still no luck matching 1/4 or 1/2 wave on UHF. But again, good on VHF, so its the APRS antenna now.


Title: RE: Fiberglass Camper Shells & Antennas
Post by: K6CPO on September 19, 2016, 11:51:14 AM
I have a fiberglass shell on my truck and I mounted a single 2 meter/440 antenna in the middle of the cab roof.  I've seen other truck owners get good results from mounting a half-wave antenna on the edge of the hood.  I have a second mount on the driver's side of the hood ready to use if I ever need it.


Title: RE: Fiberglass Camper Shells & Antennas
Post by: VE3HIX on September 21, 2016, 12:36:04 PM
There is more to this than getting a good ground plane or a 1:1 match, if the non-metallic cover is over a passenger compartment. In Europe, you need to shield the passengers from RF. A non-metallic roof would require a completely shielded liner such as the covered metal liner inside a military Land Rover that has a fiberglass top. Even a soldered connection to an NMO inside a truck roof with a steel top exposes a tiny bit of RF to the passengers, and must be shielded.

If the installation is on the back cap of a pickup truck with no passengers underneath, please disregard.

Just a heads-up.

Cheers,
Bob
VE3HIX