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Old 11-27-2013, 08:38 AM   #1
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Do cobra 75's generally have more static?

I've had a cobra 75 in my jeep for a while now and I have to turn the SQ way up to not even hear static. Fast forward, I instill a Uniden 520 in my wife's jeep and I can have the SQ almost barely turned up with ZERO static. Not to mention the Uniden sounds more clear than the Cobra.

The only install differences between the two was my wife's is mounted above the rear view mirror. Therefore, I had to run the coax along the top sport bar where in my jeep I ran the coax underneath the carpet. Both runs of coax are straight runs with no loops, etc. The other difference is I got a 4' firestick for my wife's jeep and I got a 3' fire stick.

Do you guys think that could be my issue, or is the cobra 75 a lower quality unit compared to the uniden? I'm about to grab a 4' antenna for my jeep, see if that works and if it doesn't just junking the cobra and getting a Uniden. Thoughts?

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Old 11-27-2013, 11:48 AM   #2
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the firestik is tuned to length, but there are some caveats - they even suggest the 4' over the 3' when possible.

Do you have any kinks in the coax? The remaining cable, ideally, is "s" gathered and kept from touching sides - don't just gather it up and zip-tie it, certainly don't trim it! You should have an 18' coax cable, too...

You can contact Firestik - the engineers there are VERY helpful to get your setup tuned and offer tricks and tips. Good people - they made me a Firestik customer for life.

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Old 11-28-2013, 02:36 PM   #3
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First, the 18' coax cable length thing is nothing more than an old wive's tale. Not to mention that 18' is not even a multiple of the CB's 11 meter wavelength. The correct length of coax cable is the length it takes to connect the CB to the antenna with a little slack left over for future changes or needs.

And the length of antenna will have nothing to do with static, absolutely nothing. My CB is static free with my 2' Firestick FS-2 antenna.

What does the static sound like? Does the static start when you start your engine? If so, are you running aftermarket ignition wiring or no-resistor spark plugs?

How is the CB getting its power? Only by powering the CB directly from the battery can you be assured the CB is getting clean noise-free power. Many of the circuits in a Jeep you can get 12 volts from are too electrically noisy for a CB.

One more problem that can introduce noise into a CB is via the antenna mount when it isn't sufficiently grounded. An antenna mount's grounding requirements are more demanding than something like a light bulb would require. The mount needs a good bare metal to bare metal connection to what it is bolted to. And depending on what kind of antenna mount is between the antenna itself and the body mount, the bottom half of the antenna mount must also have a bare metal connection to the mount.

A picture of the type of antenna mount you have would be helpful.
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Old 11-28-2013, 08:08 PM   #4
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It is the teraflex mount. I'm going to mess with the mount again, but I don't think it will help. Static is there regardless if jeep is running or not.
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Old 11-30-2013, 11:38 AM   #5
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It is the teraflex mount. I'm going to mess with the mount again, but I don't think it will help. Static is there regardless if jeep is running or not.
You have to file all of the powder coating off on at least one of the holes that touch the door or you really can't tune the antenna. Those brackets have pretty thick powder coating so it's not getting a good ground.
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Old 11-30-2013, 01:16 PM   #6
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You have to file all of the powder coating off on at least one of the holes that touch the door or you really can't tune the antenna. Those brackets have pretty thick powder coating so it's not getting a good ground.
I did that on the surface. My SWR on the cobra is around 2~. I was able to get my wife's SWR hell pretty much below .5. I was amazed. I've got my new tire carrier coming and it comes with a CB bracket. So we will revisit this grounding business when it comes in. If no dice on that I'm going with a 4' antenna.
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Old 11-30-2013, 04:45 PM   #7
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I did that on the surface. My SWR on the cobra is around 2~. I was able to get my wife's SWR hell pretty much below .5. I was amazed. I've got my new tire carrier coming and it comes with a CB bracket. So we will revisit this grounding business when it comes in. If no dice on that I'm going with a 4' antenna.
Yea the best I could get my Cobra 75 was down to about 1.2
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Old 12-02-2013, 09:57 AM   #8
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Going to a longer antenna won't help your issue in the least. I'll almost guarantee your problem is antenna mount related. Post a couple good sharp well lighted close-up photos of the top & bottom of the mount and we may be able to figure out the problem. At the least I can tell you where you need to grind the mount's powder coating away so the right parts will be grounded
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Old 01-11-2014, 08:22 PM   #9
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Quote:
Originally Posted by 302 View Post

I did that on the surface. My SWR on the cobra is around 2~. I was able to get my wife's SWR hell pretty much below .5. I was amazed. I've got my new tire carrier coming and it comes with a CB bracket. So we will revisit this grounding business when it comes in. If no dice on that I'm going with a 4' antenna.
I may be confused, I thought that SWR was the ratio of max to min of the reflected energy and the best you would see is 1:1 meaning no HF reflection at the antenna termination so max power to the antenna. You may want to check your meter
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Old 01-12-2014, 11:21 AM   #10
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Mak, you're not confused. The best you can do is 1:1. Meter is probably fine, it's the reading of the meter.
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Old 01-20-2014, 10:39 PM   #11
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Once you remove the powdercoat, is there anything you can put on the metal to inhibit rust that will last more than a couple weeks.
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Old 02-05-2014, 09:34 PM   #12
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Once you remove the powdercoat, is there anything you can put on the metal to inhibit rust that will last more than a couple weeks.
I would imagine you could use dielectric grease.
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Old 02-05-2014, 11:15 PM   #13
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I would imagine you could use dielectric grease.
Dialectic grease is not a good conductor it is actually the opposite of a good conductor. If you want to use something to inhibit rust, while maintaining a good electrical connection, look at something like MG Chemicals 847 Carbon Conductive Assembly Paste.

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