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Thread: CB antenna
07-24-2012, 06:47 AM #1
I am thinking about installing a CB radio in my truck. It will be a CX75 WX St unit that will be mounted under my seat. The mic has the controls mounted to it. The only time I can see using it would be on trail rides to keep myself and the trucks around me informed of any issues on the trail. Because it won't be used like a trucker I want all the equipment to be hidden. Yes that includes the antenna. I found this how to on how to use the stock antenna location for the CB antenna mount. As I am not an electrician and also a technotard I was hoping someone could shed some light on whether or not this will work. Again I don't need to be able to transmit and receive for miles or anything like that.
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07-24-2012, 07:11 AM #2
thats a interesting thought, might have to look at this for mine. the other thing you may want to look at is some sort of swing away mount in the bed. tucked under the bed rail when not in use, and out when it is. something im looking at for mine now.
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07-24-2012, 09:10 AM #3
07-24-2012, 09:11 AM #4
No. this will burn the final transistors out in your CB. If it is a newer CB, it probably won't even transmit. Why? read on...
Antennas are "tuned" for maximum efficiency. In the FM broadcast band, the electronic length of the antenna needs to be about 27" at 1/4 wave. Receiving on an improperly "matched" antenna will not cause any harm. It CAN cause poor reception depending upon how far it is away from the proper length.
TRANSMITTING, on the other hand, is a totally different story. When you transmit on a mismatched antenna, there is power left over that gets reflected back into the radio. It is like hooking 2 CB radios (or any amplifier for that matter) together and forcing one's power into the output of the other.
Think of it this way... If you and I have 2 identical brass bells and I ring mine right next to yours, then I mute mine with my fingers, you will hear yours resonating from the sound vibrations from mine. If you have 2 different sized bells, this won't work. The same principal applies to antennas. Your antenna must be tuned to resonate on the frequency that you are transmitting on.
This is where the SWR meter comes in. SWR stands for "Standing Wave Ratio" and basically measures the amount of reflected power coming back to the radio from the antenna. As your antenna gets closer to the correct length, the SWR lowers because more power resonates off of the antenna and less of it comes back to the radio.
Additionally, you can't "split" the coax and use one end to hook to the CB and the other to your stereo. If you do, you will fry the stereo the very first time you press the transmit button on the CB.
Transmitter antennas that are less than full wave also need what is called a "Ground Plane" in order to radiate the correct pattern. Otherwise, you will make the system "directional", meaning that you will radiate most of your power in one direction while almost none in another. CB antennas are most happy in the center of your roof or deck lid. Not on the edge of a fender.
Even if you modify the entire antenna with CB antenna parts, it still won't work very well. You would be miles ahead to get a magnet mount antenna and keep it in your truck than you would be to try to modify a broadcast band antenna. A good magnet mount antenna will be much cheaper than replacing your CB too.
Here's a link to a great article from Firestik: http://www.firestik.com/Tech_Docs/am-fm-cb.htm
I hope this helps.
Last edited by moogvo; 07-24-2012 at 09:32 AM."It went together didn't it? Well then there has to be a way to take it apart!" - Me.
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07-24-2012, 10:48 AM #5
@moogvo Thank you for your informative reply. I just want to make sure we are talking the same thing. I was going to use an actual CB antanna. I am going to lay my OEM antenna down like @SurrealOne did to his ride. If this changes anything please let me know. If you have any suggestions other than the rust inducing magnet mount that would be greatly appreciated.
07-24-2012, 10:57 AM #6
Yeah, that does change things. It will still radiate a weird pattern but you should be able to get your SWR down to a reasonable level. Note that a mag mount won't pull rust through the paint unless you leave it on for a long time. It won't scratch the paint if you keep it clean and a good coat of wax on the truck!
07-24-2012, 11:04 AM #7
Thank you moog!! Keeping it clean is not an issue. I just like things stealth like.
07-24-2012, 11:29 AM #8
@moogvo, I've been toying with the idea of a CB for a while ... mostly for SHTF reasons. I'm nowhere near ready to touch that, yet ... but when I am do you mind if I pick your brain on the subject?
07-24-2012, 11:41 AM #9
In any case... Yes, I will give you the best advice I can with your CB install! ;)
07-24-2012, 11:50 AM #10
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