A much easier proof is to note the fact that a decent mag mount CB antenna can be tuned to a SWR under 1.5:1 when placed in the center of the vehicle roof, without installing any ground straps between the antenna base and the vehicle body. If you were correct, that would be impossible.
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Somewhat new to CB’s, question about setup.
- Thread starter ClemsonSCJ
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A much easier proof is to note the fact that a decent mag mount CB antenna can be tuned to a SWR under 1.5:1 when placed in the center of the vehicle roof, without installing any ground straps between the antenna base and the vehicle body. If you were correct, that would be impossible.
prcguy
Member
At HF frequencies including CB, there is simply not enough capacitance between the magnet and vehicle surface to equal a direct grounded connection. In these cases the coax is part of the counterpoise and will have some RF on its shield. You can prove this using an RF current probe along the coax and you will find RF peaks and nulls.
I think the comments about scraping paint were more for fun and not a serious recommendation.
I think the comments about scraping paint were more for fun and not a serious recommendation.
FiveFilter
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Internet advice can be funny, if not tragic. Scraping off the paint to use a mag mount. Come on.
Many thousands of magnet mount antenna users know that without scraping off the paint or anything else, just plopping the magnet onto the painted roof will provide an antenna that will work about as well as any other antenna of the same length.
While it is true that a magnet-mount antennas will be a tiny bit less efficient than a hole-in-the roof model, the effect is only about 0.1dB additional loss when compared to the permanent mount. This 0.1dB loss isn't going to be noticeable by anyone except maybe a neurotic studying the meter with a magnifying glass.
The only real issue with mag mounts is routing the coax cable into the cabin. Since I only deploy my CB rigs on highway trips and remove them when not, I bring the coax through a slightly lowered rear window and use a small split hose on the top of the glass to eliminate any wind whistle and rain intrusion.
I always make sure that the radio's chassis is grounded when using my mag mounts. This can help with any common mode currents. I've never had to use coils or filters or such.
All of this works very well for me, even when I use a little RM 203 amp for the extra range and clarity when conditions warrant.
Many thousands of magnet mount antenna users know that without scraping off the paint or anything else, just plopping the magnet onto the painted roof will provide an antenna that will work about as well as any other antenna of the same length.
While it is true that a magnet-mount antennas will be a tiny bit less efficient than a hole-in-the roof model, the effect is only about 0.1dB additional loss when compared to the permanent mount. This 0.1dB loss isn't going to be noticeable by anyone except maybe a neurotic studying the meter with a magnifying glass.
The only real issue with mag mounts is routing the coax cable into the cabin. Since I only deploy my CB rigs on highway trips and remove them when not, I bring the coax through a slightly lowered rear window and use a small split hose on the top of the glass to eliminate any wind whistle and rain intrusion.
I always make sure that the radio's chassis is grounded when using my mag mounts. This can help with any common mode currents. I've never had to use coils or filters or such.
All of this works very well for me, even when I use a little RM 203 amp for the extra range and clarity when conditions warrant.
bpittman
Member
Clem,
A lot of good advice here if you were looking to get an extra S unit on a weak signal in eastern Europe! I've been working CB part time since you needed to apply for a license (to be legal). Todays technology on something as simple as CB stuff your setup will be fine with the Wilson antenna on the roof where you can get as flat as possible. These mag mount antennas are designed to be mounted on painted metal surfaces. One poster is correct in saying the metal mag base has a thin plastic coating, to protect the painted auto surface. If one was going to go to the effort to scrape the paint off and weld, why not drill a hole in the roof, install a NMO mount (or whatever the call them) install a quality fiberglass rod and run the coax across the roof inside? With your equipment you will be fine with what you are doing, just lay the antenna down before driving into the garage!
A lot of good advice here if you were looking to get an extra S unit on a weak signal in eastern Europe! I've been working CB part time since you needed to apply for a license (to be legal). Todays technology on something as simple as CB stuff your setup will be fine with the Wilson antenna on the roof where you can get as flat as possible. These mag mount antennas are designed to be mounted on painted metal surfaces. One poster is correct in saying the metal mag base has a thin plastic coating, to protect the painted auto surface. If one was going to go to the effort to scrape the paint off and weld, why not drill a hole in the roof, install a NMO mount (or whatever the call them) install a quality fiberglass rod and run the coax across the roof inside? With your equipment you will be fine with what you are doing, just lay the antenna down before driving into the garage!
FiveFilter
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Quote: ",,,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 that’s the direction I’m 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 can’t complain...."
With the antenna on the rear portion of the roof, your setup probably will transmit a better signal to the front, To me, this is better for someone traveling who wants road condition information about where he's going. He already knows what conditions are like where he's been. At least, that's my logic.
As far as receiving a signal, I doubt the antenna placement will make a difference. It's important for the transmitting signal, not so much the receive. At least, that's what I've been told.
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 can’t complain...."
With the antenna on the rear portion of the roof, your setup probably will transmit a better signal to the front, To me, this is better for someone traveling who wants road condition information about where he's going. He already knows what conditions are like where he's been. At least, that's my logic.
As far as receiving a signal, I doubt the antenna placement will make a difference. It's important for the transmitting signal, not so much the receive. At least, that's what I've been told.
jhooten
Member
SWR is not a reliable indicator of antenna resonance or efficiency. While SWR can be low enough to let the transmitter be happy, that does not mean the antenna is an efficient radiator. A dummy load has very low SWR but you won't "get out" very well using one.
BTW, Very few vehicle roofs are big enough to act as a ground plane for a CB antenna. Unless of course your vehicle is over eighteen feet wide.
And yet, it is not that difficult to install a decent-performing CB antenna on a vehicle anyway. A mag mount may not have enough capacitance to run at ideal efficiency, and the vehicle body may not be a perfect ground plane, yet despite those limitations, a mag mount CB attached to the center of the roof of most vehicles will perform reasonably well if you do basic tuning. it won't perform as well as a 1/4-wave vertical with a 18' diameter ground plane, but it will work well enough to do the job in most cases.
jhooten
Member
The definition of decent performing is in the eye of the beholder. Some users are happy to be able to talk across the median to get current traffic updates/smoky reports. Some people try to make up for their decent performing antennas by running shortwave broadcast station power levels.
Depending on what the job is, yes.
Depending on what the job is, yes.
jhooten
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ClemsonSCJ
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mmckenna
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Yeah, pretty much.
Radio can be easy or as complicated as you want it to be. If you want it easy, you are going to have a hard time really squeezing the most range out of it. Understanding the technical side lets you get down into the nitty-gritty and get the most our of your setup.
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