mobile antenna option, 800 mHZ primary w/ vhf secondary, no ground plane reqd?

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dizwiz

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I have a 92 corvette convertible.

I currently run coax up through the windshield pillar, comes out the weatherstrip and then terminates into a BNC connector which is attached to an 800 MHZ ANTENNEX rubber-ducky antenna at the top most point of my windshield frame..

It actually doesnt look too bad either as the antenna extends off the windshield frame at the same angle as the windshield frame 'rake' angle (prob not best for reception, but looks good).

This works 'good' for what it is. I am not expecting stellar reception out of this low-ride height fiberglass vehicle.

However, Id like to know if there are better antenna options. Ive seen the long CB antennas that are built into a special frame behind the rear license plate. However, I dont care about lo-band CB.

Mounting something to the frame or rear deck lid - forget about it. Not worth it to me. Also, its a convertible so, I cant just put a roof antenna on w/ wires through the t-top (targa) top panel. ...

Does anyone have any recommendations on 800 MHZ (primary freq) w/ vhf (150 mhz) secondary capability antennas that do not require a 'metal' ground plane.

Well, I guess a metal ground plane would be ok if the steel windshield frame 'counts' as a ground plane. Though Im not sure it would (correct me if im wrong)

The smaller the antenna the better
 

Rt169Radio

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I use the Larsen tri-band antenna for scanning and it works good and it is sturdy.Its MHz range is 150/450/800 and its quite short.
 

dizwiz

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Thats an NMO mount.

Isnt that the kind that requires a giant hole be drilled in the car?

Also, doesnt it rely upon a ground plane?
 

W9BU

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Thats an NMO mount.
Yes.
Isnt that the kind that requires a giant hole be drilled in the car?
3/4" diameter
Also, doesnt it rely upon a ground plane?
Yes. However, your car is not entirely fiberglass. If the antenna mount was bonded to the frame, it might work OK. Not as well as if the antenna mount was in sheet metal, but it might work. Also, it has been fairly common practice when installing antennas in the fiberglass roofs of ambulances to install a ground plane made of sheet metal on the underneath side of the fiberglass.
 

dizwiz

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Ok. i thought of a unique solution to my dilemma.

Tell me what you all think:

I just realized the fuel filler door, at the top of the rear deck lid, is metal.

This is a 6" x 9" flat metal piece, in an easily unboltable carrier, that is attached to the otherwise fiberglass rear bumper assembly.

While 6" x 9" may seem like a small ground plane, its better than nothing. Also, I can attach a ground strap from it to the frame of the car for even better reception.

I will buy a spare one, drill a 3/4" hole in it for the NMO mount, and mount that Larsen antenna that was recommended in an earlier thread.

The antenna will be off the rear decklid (not as good as roof mount, but better than other options)

If Im going to a car show or something, just swap the original fuel filler door lid back in place since it bolts up so easily.
 

W9BU

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That's a reasonable plan.

Larsen, Antenex, and other mobile antenna manufacturers offer NMO "rain caps". I like the Antenex ones because they are very low profile and available in chrome or black. Unless you are taking the car to a strictly-judged car show, it might be easier to just screw on a rain cap than swap out the door.
 

dizwiz

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Im actually pretty fired up about this idea:

Parts for this 'older' corvette are actually fairly cheap since its in-between the current model and classic corvettes. So I buy another one (from a wrecked corvette or something) so I wont have to 'butcher' my OEM one up.

heres a picture of the fuel filler door: (Actually its prob about 6 "x 11" metal. It must be aluminum since a magnet wont stick to it).


heres a picture of it 'opened'.... plenty of space to route the underside of the NMO mount and wires.


heres a picture of where it goes on the car


again, totally simply to unbolt this assembly.
 

c5corvette

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I did that same project with my C4 during the National Corvette Caravan. Mounted an UHF quarterwave there for caravan communicaitons back and forth with the lead car up front. Its pletny of ground plane for RX, I was using it for TX too.

If youre just using a scanner, you can strip a piece of coax back about 15 inches and tape it to the inside of the car body in the back (you will need to pull back some carpet in the rear area under the soft top, or run it all the way back to the rear quarterpanel, but I have done this and it works well through fiberglass.
 
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