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  #1 (permalink)  
Old 05-29-2018, 9:49 AM
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Default Somewhat new to CBs, question about setup.

Hey guys Ive been running a CB in my vehicles for several years now but have never really done much research into other than setting SWR. I know how to do that but dont have much knowledge beyond that. Im wanting to get a new set up in my Jeep Grand Cherokee and want to know if it sounds efficient, mainly the antenna aspect.

Im gonna be running a Cobra radio, totally stock, a TNT 350HD amp, and a Wilson 2000 Trucker antenna. The main question I have is in regards to my antenna location. I have a mount from a Jeep accessory company that mounts the antenna on the back between the gap of the tailgate and side panel just above the tail light ( The Steel Armadillo LLC > Jeep Grand Cherokee (WK) 2005-2010 > Steel Armadillo CB Antenna Mount ). With the 10 shaft that comes with the Wilson 2000 the coil will be about 9-12 below the roof of my car. Will that be a major issue with TX, RX, and setting a good SWR?
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Old 05-30-2018, 12:04 PM
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Come on guys, just needing to know if the coil being slightly below the roof of the car is going to be an issue.
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Old 05-30-2018, 5:08 PM
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if the roof is fiberglass probably not,,,,
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Old 05-30-2018, 5:21 PM
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Major issue? Define major.
If you have an unbroken metal roof the best place for the antenna is about the middle of it. Putting any part of your antenna below the ground plane (roof) is not ideal.

And then again, you realize that simply having that amp hooked up can result in a $10,000 fine. If you're running that much transmitter power, it may be a problem because it is radiating into your ground, into the car.
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Old 05-30-2018, 5:34 PM
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Originally Posted by ClemsonSCJ View Post
With the 10 shaft that comes with the Wilson 2000 the coil will be about 9-12 below the roof of my car. Will that be a major issue with TX, RX, and setting a good SWR?
Most likely yes. Having the antenna below the roofline will increase SWR, decrease RX and TX performance, and increase the amount of RF radiating into the passenger compartment. All of those are bad, especially if you're running extra power.

Put the antenna in the middle of the roof.
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Old 05-30-2018, 7:05 PM
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Major issue? Define major.

If you have an unbroken metal roof the best place for the antenna is about the middle of it. Putting any part of your antenna below the ground plane (roof) is not ideal.



And then again, you realize that simply having that amp hooked up can result in a $10,000 fine. If you're running that much transmitter power, it may be a problem because it is radiating into your ground, into the car.

Roof has a sunroof so not sure if thats what you mean by an unbroken metal roof.

As for the fine...always been curious how someone comes in contact with such a person who would issue said fine? If you get pulled over, even if the cop knew what you had, he cant enforce it. Who else is gonna be going through my car?
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Old 05-30-2018, 7:05 PM
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Originally Posted by jonwienke View Post
Most likely yes. Having the antenna below the roofline will increase SWR, decrease RX and TX performance, and increase the amount of RF radiating into the passenger compartment. All of those are bad, especially if you're running extra power.



Put the antenna in the middle of the roof.

Ive heard sunroofs cause problems there as well.
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Old 05-30-2018, 7:25 PM
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Lowering your SWR isn't the only measure of a good antenna installation. You also need to consider the radiation pattern that you are creating with the mounting location.

If you are going through all this effort, and then adding an amplifier with the idea of communicating longer distance, then cutting corners by using a clamp on antenna mount installed in a poor location is counterintuitive.

If you want your signal to radiate well in an omnidirectional pattern, you need to have your antenna mounted in the center of your ground plane, not off to one end. By mounting off to one end, you are creating a directional pattern. Whereas if you install it dead center, it's going to radiate much better in all directions.
The other benefit is that if you are going to be running an amplifier, you need to put some effort into keeping that energy out of the vehicle wiring and away from the driver and passenger. Hanging it off the rear of the body near a window isn't going to do that. Mounting it on top in the center is.

Use a base loaded whip if you can with the roof mount.
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Old 05-30-2018, 7:47 PM
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Originally Posted by mmckenna View Post
Lowering your SWR isn't the only measure of a good antenna installation. You also need to consider the radiation pattern that you are creating with the mounting location.

If you are going through all this effort, and then adding an amplifier with the idea of communicating longer distance, then cutting corners by using a clamp on antenna mount installed in a poor location is counterintuitive.

If you want your signal to radiate well in an omnidirectional pattern, you need to have your antenna mounted in the center of your ground plane, not off to one end. By mounting off to one end, you are creating a directional pattern. Whereas if you install it dead center, it's going to radiate much better in all directions.
The other benefit is that if you are going to be running an amplifier, you need to put some effort into keeping that energy out of the vehicle wiring and away from the driver and passenger. Hanging it off the rear of the body near a window isn't going to do that. Mounting it on top in the center is.

Use a base loaded whip if you can with the roof mount.


Will a sunroof in the middle of the roof affect where I need to put the antenna? If Im gonna mount on the roof then Ill probably go with the Wilson magnet mounts.
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Old 05-31-2018, 12:04 AM
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If you are new to CB ,someone gave you bad advice about using an amp telling you you're going to talk farther.... classic 11m misconception.
Even if you're driving more output power this won't make you hear more,so if you can't talk to someone you don't hear, you're just likely to make your signal slightly higher to the ones you can hear that's all. And if that unit has a preamp on receive they usually just amplify the noise.

Plus with that type of amp and your antenna placement you are going to get all sorts of RF problems.

Putting your antenna in an ideal location first is your best solution like others mentioned.
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Old 06-01-2018, 12:45 PM
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I use a couple of mag-mount Wilsons with great results. Get yourself a Wilson 1000 or 5000 and plop it on the roof. Check the SWRs and compare locations. Generally, in the middle is a great place. Mine are usually in the middle of the roof slightly towards the rear as I'd rather talk ahead of me when I ask for road information. I doubt the moon roof will make much difference. Go for it!

And about the fine, it's a strawman factor. Nobody's going to bother you because of your amp, especially in a mobile unit. Now, if it's a base station and is bothering the neighbors, the chance begins to raise the meter off of zero. If it's a base unit near an airport, the meter of possibility might start bouncing off the high end.
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Old 06-02-2018, 3:52 AM
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Quote:
Originally Posted by 599 View Post
If you are new to CB ,someone gave you bad advice about using an amp telling you you're going to talk farther.... classic 11m misconception.
Even if you're driving more output power this won't make you hear more,so if you can't talk to someone you don't hear, you're just likely to make your signal slightly higher to the ones you can hear that's all. And if that unit has a preamp on receive they usually just amplify the noise.

Plus with that type of amp and your antenna placement you are going to get all sorts of RF problems.

Putting your antenna in an ideal location first is your best solution like others mentioned.

Ive actually never been given advice. Ive been running a CB in my car since high school (little over 10 years) and never did much research into it. Hell Id be willing to speak for a lot of people who probably have no idea something as simple as a CB radio could be as complicated as it is. Most people think radio...antenna...bam, done. Im not even sure how I came across SWR and knowing that it had to be adjusted but somehow I at least got that.

As far as the amp, thats something I discovered on my own but I just know my buddy and I who had to talk on our CBs all the time never could get more than a few short miles apart before we couldnt hear each other at all. Then I ended up getting a Palomar Elite amp and he got some other brand I cant remember from a local shop. After that, as long as weather conditions werent crappy, most of the time we could talk to each other clearly from or houses which were 15 miles apart. After looking into efficient setups now, I know my setup then wasnt efficient at all so now that I plan to do things properly well see how much better results I get.
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Old 06-21-2018, 10:16 AM
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*****************UPDATE****************

I wound up going with the Wilson 1000 magnet mount and am gonna forgo the amp for now. May explore that option later but not right now. I just got done hooking it up and tuning the SWR and at first was having issues getting it below 2. I had previously read that magnet mounts get their electrical ground from the contact between the magnet base and the metal roof. I figured that was where my issue was because the roof of my Grand Cherokee has raised ridges across the roof so the magnet was not able to get a flat mount. Kinda a bummer cause I was wanting to keep it in the center of the roof so I had an equal ground plan in every direction. I ended up having to move it towards the very back of the roof where the ridges stop. I could have gone forward however I have a sunroof so I would have had a diminished ground plane in the forward direction and thats the direction Im most likely to want the best signal.

Anyways, once I moved the antenna and got it mounted flat to the roof, I ended up getting the SWR down somewhere between 1.2 and 1.3 so I reckon I cant complain. Thanks for everyones help!
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Old 06-21-2018, 7:00 PM
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You have to scrape away the paint down to the bare metal for the magnet base to make good ground contact.
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Old 06-21-2018, 7:55 PM
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You have to scrape away the paint down to the bare metal for the magnet base to make good ground contact.
No. The sheet metal and the base of the magnet form the plates of a capacitor, which is designed into the tuning of the antenna. Scraping the paint off the roof defeats the whole point of a magnet mount antenna, and can actually detune the antenna.
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Old 06-21-2018, 8:40 PM
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I prefer to tack weld the mag mount to the roof after removing the paint. I also like to tack weld the shield of the coax to the roof for extra bonus points grounding.

Otherwise it can be difficult but not impossible to match an antenna using the mount in your link. The finished product will be somewhat directional toward the opposite front side of the vehicle due to the vehicle ground plane pulling the radiation pattern down toward the horizon over the mass of the vehicle.

Most of the radiation from the antenna you have chosen will be below the coil and not above, but blockage in this case is not a big deal. The blockage is very small with respect to wavelength and signals toward the rear of the vehicle will be worse than to the front anyway.

One of the challenges of the mounting you chose is keeping RF off the coax and that would need to be addressed before lighting up an amplifier in the vehicle. You can usually cure hot coax with proper application of ferrite like wrapping the right number of turns through the right ferrite mix and placing that at a critical point in the coax. I can give more info on that if your interested.

If you go with a mag mount and are worried about grounding, you can easily increase the ground coupling of the mount to the roof with a home made capacitor plate. You can get enough RF coupling to where you can't measure any difference in tuning or performance compared to the same antenna drilled into the roof and hard grounded.

To make a capacitor plate get a sheet of thin flexible magnet material as used on refrigerator magnets. You can get an 8 1/2 X 11" sheet off Ebay cheap and make sure it has one side with peel and stick adhesive. Then get a thin maybe .003 to .005" thick copper sheet off Ebay then glue the copper sheet to the magnet, cut it in half (8 1/2 X 5 1/2" is plenty big for 27MHz) then solder a very short but wide flexible braid to the edge of the copper sheet magnet and attach it to the grounded side of the mag mount.

Whatever ground coupling the mag mount had will be increased several times by the capacitance of the magnetic copper sheet and the antenna will think its got a direct ground connection at its base, tuning will be easier and better, performance will be better and you should have no hot coax.

I've done the capacitor plate trick on several ham antennas and a full size 8 1/2 X 11" sheet will make an 80m (3.8MHz) whip on a mag mount think its got a direct ground connection. The higher in frequency you go the less coupling you need.

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You have to scrape away the paint down to the bare metal for the magnet base to make good ground contact.
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Old 06-22-2018, 2:47 PM
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No. The sheet metal and the base of the magnet form the plates of a capacitor, which is designed into the tuning of the antenna. Scraping the paint off the roof defeats the whole point of a magnet mount antenna, and can actually detune the antenna.
Try to keep up. He said he was told the ground was from the magnetic base making direct contact with the metal of the body. For that to happen, yes, you will need to remove the paint as most auto body paint is non-conductive.

Next nit-pick. A four inch magnet base does not give enough area to provide much capacitance to couple an HF signal to the vehicle body panel even with an insulator as thin as a layer of paint. In the vast majority of cb installations using a mag mount the rf ground is made through the negative power wire. One of the reasons fir inconsistent SWR indications.
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Old 06-22-2018, 8:06 PM
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Try to keep up. He said he was told the ground was from the magnetic base making direct contact with the metal of the body. For that to happen, yes, you will need to remove the paint as most auto body paint is non-conductive.
I'm well aware of what he was told, and it's total BS. End of story. Scraping the paint wouldn't be enough anyway, as most mag mount antennas have a non-conductive plastic film applied to the contact surface of the base to reduce the possibility of scratching or marring the vehicle paint. If you want direct electrical contact instead of capacitive coupling, you can't just scrape the paint off a 4-inch circle of the roof (which is going to rust quickly), you'd need to remove the plastic film off the mag mount base, too.

Quote:
A four inch magnet base does not give enough area to provide much capacitance to couple an HF signal to the vehicle body panel even with an insulator as thin as a layer of paint. In the vast majority of cb installations using a mag mount the rf ground is made through the negative power wire. One of the reasons fir inconsistent SWR indications.
Actually, the whole point of the vast majority of mag mount installs is to get a working antenna without damaging the vehicle paint, or drilling holes for antenna mounts or ground wire screws. Your first sentence is wrong, and the following sentences are a good explanation of why jerry-rigging a ground wire to a mag-mount antenna that isn't designed for one is a bad idea.

If scraping away a 4" circle of paint for a mag mount base is OK, then drilling a <1" hole for a permanent mount would be even okayer. If marring the paint is not an option, then you use a magnetic mount antenna, and you don't scrape paint off or drill holes to attach RF ground wires.
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Old 06-22-2018, 8:12 PM
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Folks, if you aren't going to provide serious and useful responses to the OP's question, perhaps you should keep your comments to yourselves.
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Old 06-22-2018, 9:57 PM
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Your first sentence is wrong,
Prove it. Calculate the capacitance yourself. Show your work.
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