Gearhead Jim

Mid-America will sell me a CB antenna and a mount that fits behind the rear license plate, for only $169. (!)

But I already have the antenna, just need something/someplace to mount it. My little window-edge clamp wouldn't work on my C5 and i don't think it will work on the C6. Except for the license plate mount, is there any other way to mount the antenna outside the car? I had it horizontally in the trunk cargo net (!) of my C5 and it worked but range was pretty limited. Also tried shorty antennas inside the car and didn't like them either.

I could make an angled piece of aluminum to fit behind the license plate similar to the Mid-America mount, but probably someone else is already making them better than i could. Can you tell me where to get one?

BTW, I only use CB for keeping in touch with the other cars in our club on trips. I agree with those of you who think it's pretty useless otherwise so we can save some bandwidth and skip that discussion...

Indy-hp

I showed a handy friend of mine a picture of the Mid America C5 license plate CB mount and he made me one out of a scrap piece of sheet stainless steel. Even if I had paid for the steel, it shouldn't cost more than $20. Cut out triangle shape, drill 3 holes, bend at 85 deg. angle, done. It would probably cover the keyhole and latch button, but for club road trip use only, that is no big deal to me.

Tin Star

http://www.hamstick.com/ then click "products" followed by "mounts" (check lic plate mount and flat bar mount)

V Vette

Whats a CB???????

1fastLT

CB=Circuit Breaker.... My question is why you need one and why would you mount it by the license plate???

LS WON

You can try one of those glass mount antennas that are mounted onto your glass. It won't ruin the lines of the Corvette as much as that CB antenna will.

Gearhead Jim

I've been told that the glass-mount antennas loose a lot of performance, but I can't verify that. Do we have any antenna wizards here?

LS WON

Because it is a Corvette it presents a problem(Fiberglass) normally a magnetic mount like a K-40 is a great antenna on metal cars but there are only 2 other choices for CB the ugly mounted one on the license plate or the less evil the glass mounted antenna.

Gov'sGuy

Jim,

I don't think you'll get good range from pretty much any antenna you mount on a Corvette. Most all antennas need a ground plane to both ground the antenna and to act as a sort of mass sink. A ground plane isn't a problem for most cars because of the steel body, but with the Corvette's fiberglass body you just can't do that.... even with your license plate mount.

You should have better luck with your interior antennas by running a good frame ground wire to the antenna mount; solder or braze a wire lug to the mount... some exterior antenna mounts have a ground lug already attached.

NOTE: Don't use a ground from an electric circuit..... if you do you may need to install an in-line filter to block ignition feedback.

That should get you better RF performance.

Good luck
Al

xs650

A 1/2 wave tuned antenna should work good without a groundplane. I think a 5/8 should too. I agree that a regular CB antenna won't work up to it's potential on a Corvette.

shopdog

Halfwave antennas are ground independent, 5/8-wave antennas aren't. That's why fiberglass boats typically use halfwave antennas. Works for fiberglass cars too.

One important tip, though. You must use a current balun to feed the antenna. A current balun is a special kind of choke that prevents RF currents from flowing on the outside of the coax shield (transmission line currents flow on the inside of the shield, skin effect prevents them from bleeding to the outside until they reach the end of the cable, then they can turn around if you don't choke them at that point). The feedpoint of a halfwave antenna is high impedance, which requires a matching network at the antenna base, and if you don't include a current balun, the coax shield will be hot with RF, distorting the antenna pattern, and bringing RF back into the cabin where it can raise hell with the vehicle electronics.

Gearhead Jim

"current balun" sounds like a legal term:
"Your honor, the defendant wishes to file a current balun about..."

For those of us with less (a lot less) electronic knowlege, what does one look like? The no-ground-plane antenna that I had in the C5 doesn't look unusual and is not tuneable. The instructions caution not to shorten the coax cable because the whole unit is tuned together. It gave range of about 1/2 mile, which I thought was pretty good for an antenna mounted horizontally in the trunk. There was no interference with car electronics that i could detect.

My original plan was to mount the same antenna outside the new C6 for club trips, take it off for daily driving. The license plate mount would seem to work well for that but now I'm getting confused...

shopdog

A current balun is just a ferrite toroid with 8 to 10 turns of coax cable. Amidon sells the toroids. You can get one at nearly any amateur radio shop.

xs650

Firestick sells a 1/2 wave with a special coax lead they caution you to not shorten or ground the antenna end of the shield. Does that serve the purpose of a balun, or is there one built into it? From the outside, it looks like ordinary coax to me.

donsar

If that's all that you use it for, why disfugure the car? Buy a couple of personal handi-talkie radios, assuming others in you club have them. There range is somewhat limited, but they work great within a mile or 2.

Gearhead Jim

We've tried different handhelds with unsatisfactory results. Standing out in the open you may get a mile of range, trying to transmit from inside the car, in traffic, range often drops to about 100 yards and is unpredictible.

dollarbill

I am sure that this thread would have been one of the most popular ones about 15 years ago. Today with racing radios, FRS radios, and Cell Phones - why bother???????

xs650

None of those tell you about potential LEO hazards up the road like a CB tuned to a bunch or ratchet jaw truckers does. If you can mentally filter through their jabbering, there is lot of useful information there

Cellphone don't work reliably in lot of fun places to drive. FRS radios have such short range car to car as to be virtually useless unless you are caravaning in open country.

Ray Heaton

Gearhead Jim --

If your antenna is mounted horizontally in the trunk, and you're trying to talk with someone relatively close whose antenna is identically mounted, you'll have the best results. If their antenna is mounted vertically and yours is horizontal you will have a difficult time; much signal effectiveness will be lost unless you're very close, say, within a few hundred feet. The same holds true whether you're on CB (27 MHz) or GMRS (UHF).

If you go with Shopdog's recommended fibreglass half-wave you'll have much better performance (distance). In this example a half-wave antenna is symetrical and complete; it has all it needs to function without a ground plane.

A half-wavelength straight-wire antenna at 27 MHz will be about 17 feet long (a half wavelength = 468 / frequency in MHz). To make it more manageable most of these types are "loaded"; the wire is wrapped around a glass core, like a small diameter Slinky. This shortens the length a lot, perhaps down to five feet.

A magnetic-mount quarter wavelength antenna (also loaded to make it physically shorter) still requires something to perform as the 'missing' other quarter wavelength of wire. On a metal body the other half is provided by the rooftop if it's mounted there. The rooftop is the ground plane.

XS650 -- the "special coax...they caution you to not shorten" probably includes a quarter wavelength that has the outside braid cut and "floating" (isolated from the rest of the braid) somewhere to provide the balun effect. Or it's using the length of the cable to act as a matching transformer. Or both.

Toroids are donut-shaped; if you want to try making a toroid-core current balun to work with a half-wave antenna I suggest a 2" diameter core (so you don't have to cut off and reattach the radio connector), ferrite type, mix #43. Wind the coaxial cable through the center hole and around the toroid perimeter six times. Hold the cable in place -- tight against the toroid -- with nylon wire ties or vinyl electrical tape.

It's a lot easier at VHF / UHF frequencies, where a metal-tape antenna can be temporarily "stuck" onto the inside of the rear window, or directly onto the fibreglass anywhere within the body.

Gearhead Jim

dolllarbill-
CB is the quickest way to tell things to 10 cars scattered over a mile in traffic. Other methods can substitute but not as well.