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Author Topic: C5 Corvette  (Read 3546 times)
KB2YAN
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« on: December 07, 2010, 03:03:32 AM »

Has anyone successfully mounted a dual band and antenna in a C5 Corvette coupe without drilling holes in the body or welding metal?
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K0BG
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« Reply #1 on: December 07, 2010, 06:37:35 AM »

The real problem isn't the hole-less mounting, it is the lack of a dual band antenna which doesn't require a ground plane under it. The OM series by Larsen are meant to operate fairly well without one, but they aren't dual band. If you try to use say a Larsen NMO2/70BK, you end up with the coax radiating most of the signal.

About the only thing you can do is use a frame extension mount, and hope for the best performance wise.
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AD4U
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« Reply #2 on: December 08, 2010, 09:10:32 AM »

I have a friend who has a C5 Corvette.  He installed a "through the glass" Larsen?? two meter antenna.  It radiates a signal, but don't expect too much from it. 

Typically, with this set up, my friend can communicate through my repeater no more than half the distance that he can when using his other metal vehicle with a properly installed Larsen 5/8 whip.

No wonder "through the glass" antennas are rarely seen or used today.

I also do not know of a dual band antenna that would work on a fiberglass vehicle. 

As a last resort you could try two different "through the glass" antennas, one on each corner of the rear glass.  As I said previously, don't expect too much from them.

Dick  AD4U
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K0BG
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« Reply #3 on: December 08, 2010, 03:09:07 PM »

If it was made after 2001, the Corvette has passivated glass, and the on-glass won't be any better than a rubber ducky! Even if it doesn't have, the coax ends up doing most of the radiating, with predictable results.
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KB2YAN
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« Reply #4 on: December 08, 2010, 05:56:29 PM »

It's a 2001. I don't think a glass mount will work very well.

The underside of the back hatch is metal. I'm thinking the right mount and maybe a grounding strap would work.
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W5ER
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« Reply #5 on: December 09, 2010, 05:39:32 AM »

I've got a 1991 C4, was considering using a dipole for 2 and/or 440.  RG-58 from radio, remotely mounted in back, up to the dipole adhered to the rear glass or up front to the windshield or Targa blue plastic removable roof panel. My thinking is that dipoles work w/o grounding as they are inherently self contained. So Alan, what do you think?

Haven't tried it yet, have put ZERO miles on it in 2010, had knee replaced and discover that the difficulty I had getting in and out is now multiplied many times over, XYL was thinking of taping my exit and putting it on youtube for all to enjoy.

73 Ed W5ER
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K0BG
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« Reply #6 on: December 09, 2010, 06:40:44 AM »

Ed such an antenna was made at one time. How well it worked I can't say.

One of the biggest problems with Corvettes is the lack of shielding. Even as well grounded as they are, even their AM/FM radios suffer off-air fringe problems long before most metal vehicles do. Over the years, I've seen several Corvette installs. Most were somewhat RFI noisier than I was used to. Sort of a mutually exclusive thing!
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N1DVJ
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« Reply #7 on: December 13, 2010, 09:02:17 AM »

I mounted a radio in a friends Lotus, but it wasn't easy.

As mentioned, shielding will be an issue.

I'd try to get a 1/2 wave antenna.  But 1/2 wave on both bands is going to be hard to fine.  But you may have the best luck with a 1/2 wave for 2M and then try to make a plane.  But you may not be pleased.

Through the glass are always a compromise, and as pointed out, won't work well at all with some of the new metalized glass in use.  Even then, a lot of the glass antennas rely on a capacitive ground coupling, so make sure you can get that.  In my friends Lotus, I ended up using metal under the entire panel.  We mounted on the edge of the trunk (if you could call it a trunk) and put heavy foil under the entire assembly connected to the antenna base.

It was an exercise in compromise and frustration.  

It worked, but that's about all I'll say...
« Last Edit: December 13, 2010, 09:04:00 AM by Mike Yetsko » Logged
K0BG
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« Reply #8 on: December 13, 2010, 11:40:40 AM »

Funny you should mention using metal under the antenna. I don't remember much about the install (many years ago), but it was on a dune buggy built on a shortened VW frame. What appeared to be the trunk was really where your feet went. Under the area was a large piece of aluminum sheet.

I suspect a similar scenario could be done, using copper foil tape. I'm not sure it would be as good as a steel trunk lid, but sometimes you gotta do what you gotta do!
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N1DVJ
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« Reply #9 on: December 15, 2010, 06:31:48 AM »

Hi Alan!

As I said, it was an exercise in compromise and frustration.   But you hit it exactly on the nail when you said sometimes you gotta do what you gotta do.  There was just no way to do a good installation, so this was 'an installation'.  It worked... 

I used double stick tape to line around the inside and then put aluminum foil.  What a mess.  Nowadays, if I had to do it again, I might use contact glue, and then press down some copper screen on the whole trunk and even the nearby body panels. 

Oh, I had one case that was a nightmare.  It was for a girl that wanted a CB in a Dodge Colt...  Turned out the trunk was INSULATED.  Yep, everything had standoff insulators.  Then I discovered a small coaxial cable hidden tucked up under the edge at the hinge.  Connected to  the trunk lid.  The trunk lid was the cars broadcast radio antenna!!  I ended up putting a disguise CB antenna on the fender. 
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K4KRW
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« Reply #10 on: December 16, 2010, 03:34:05 AM »

I remember reading this a while back:

From the Comet Antennas FAQ page:

A.In the past, most people preferred drilling a hole in the center of the roof or trunk to provide the best ground plane. This made a lot of sense when the repeater systems were poor and most antennas were single band and needed the ground plane. Current antenna design produces antennas that are ground independent. The sensitivity, coverage area and height of most modern repeater systems is outstanding. The antenna no longer needs to be in the middle of a ground plane for excellent coverage.
The benefit of drilling a hole and mounting your antenna in the middle of the roof or trunk is minimal.

Any comments?
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N1DVJ
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« Reply #11 on: December 16, 2010, 03:40:16 AM »

I think you'd find that antenna performance is STILL affected by position.  And if possible and there aren't other compromises involved, the center of the roof is still the best position.  It's high, it's centered...  Even without considering the effects of a 'ground plane', it's where you want the antenna to be.  (Kinda hard with a convertible though...)

I also think they are refering to the 1/2wave 2M antennas that don't require a ground plane.  A lot of the dual band antennas are 1/2wave on 2M, then some arangement of stacked elements for UHF.  Being multiple elements on UHF probably isolates them somewhat from the effects of the ground plane.

Then again, I may be wrong and I may be just spouting things that have a faint whiff of hydrogen sulphide...
« Last Edit: December 16, 2010, 03:42:24 AM by Mike Yetsko » Logged
KD5FX
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« Reply #12 on: March 23, 2011, 10:33:52 AM »

I've had a 2001 Coupe for over 5 years now. I've tried several dualband type antennas. The one that works the best is a Larson thru the glass dualbander on the back glass. It is tinted glass but I am not having a problem getting a signal through it. You must be very careful when mounting the antenna to avoid the AM antenna wires and defroster wires in the glass. I can send you a picture of my installation if you wish.
73, Dave
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