 Mounting your antenna
Mounting your antenna
ANTENNA INSTALLATION
The best place to put a single antenna is right in the center of the roof but we all know you can't get there from here in a truck.
On a semi the most common place to mount an antenna is on the mirrors, is it the best place no but you don't have a lot of choices. Some other places you might look into are the headache rack, or the exhaust bracket as these are grounded to the frame.
Installing the Antenna Mount
An antenna mount is a device that hooks your antenna onto your vehicle. Mounts are usually made of metal and have a plastic insulator which insulates the whip from ground. There are many kinds of mounts, almost as many as there are antennas. The most popular ones for trucks is the mirror mount. The mirror mount is good for getting your antenna up high where it can get out.
If you are using dual antennas you need to be 8 feet apart or your signal will go to the sides more than in front and behind this is important. (I'll bet you didn't know that)
An important thing to remember with any mount is that it must have a good ground connection between the mount and the truck frame. Some mounts have teeth that are tightened until the they dig into the mirror bracket.
The center conductor of the coax connects to the whip either directly, or through a loading coil. Neither the metal whip nor the center conductor can touch other metal
If you think that the whip might bend back and touch the metal body when your vehicle is in motion, you can insulate the section of the whip with some electrical tape or plastic tubing or adjust the antenna froward a little. (Not a lot you are not jousting)
If at all possible avoid installations where the antenna whip is up next to the trucks body.
(This means mount the antenna as far out on the mirror bracket as possible)
This is imperative for good performance. Any other antennas mounted on the mirror will absorb 10-20% or more of your power.
(Did you know that?)
Follow directions enclosed with the CB antennas you purchase. Most problems can be answered by just reading the instructions before you begin.
Coax
Now there are several types of coax, The most popular are RG-58/AU and RG-8/AU coax Unless you're running 600 watts or more in your truck, RG-58/AU will work fine. RG-59/AU is used for twin CB antenna co-phasing harnesses.
It should never be used for single antenna CB installations. The impedance is wrong and you will never get the SWR down.
It's good when installing a antenna get the coax out of the way, running it through the door is not the best way buy far to run coax. Avoid flattening or crimping or cutting the insulation on the coax.
The coax will need to be connected to the back of the radio and to the antenna. This is done with a connector called a PL 259 that attaches to the coax.
Checking the SWR
Is your Antenna Working Right? The length of your antenna makes a difference. (Not the length of coax)
When your antenna is the wrong length, some of the power does not radiate, but is forced back into the coax, and into the radio itself If this reflected power is too high, it can cause your CB's power transistors to overheat and even burn up! (Aka Blown Finals)
Besides, it's a waste of energy that you could be using to talk with.
So you want the least amount of reflected power and the most amount of forward power you can get.
It's simple. You can find if your antenna is the right length by using an SWR meter. Checking SWR First of all, you'll need a short coaxial cable with a connector on each end. Plug in one connector into your rig and the other into the socket on the meter labeled TXMTR or TX. Plug the coax that goes to your antenna into the socket on your meter labeled ANT. Turn the knob on the meter all the way down (counterclockwise). Put the switch in the forward or calibrate position. Turn on your radio to channel 1. It should be working normally. Press your mike button and, without saying anything into the mike, adjust the knob on the SWR meter until the meter reads set, or full scale. Then flip the switch to Reflected or SWR and read the SWR scale of your meter. After noting what the SWR is, stop transmitting. Then turn your radio to channel 40 and test. If the meter reads less than 1.5 on 1 and 40 your antenna is working properly. If it reads more than 2, your antenna probably needs some adjustment. If it reads more than 3 or in the red, check all connections at the antenna for possible bad connections; the antenna or the center wire of the coax might be touching the body of the vehicle, or you don't have a good ground. Coiling your excess coax into a small bundle can cause a high reading too. (It makes an electro magnet)
If this happens, the coax can be coiled into longer loops (Like a bread sack)to avoid causing a high SWR.
Adjusting Your Antenna's
So let's say that your SWR turns out to be 2: 1, and you want to bring it down. There are two ways to change an antenna's SWR: one is to lengthen it, and the other is to shorten it. You can figure out which way to go in the following manner: Take an SWR reading on channel 1, then take one on channel 40. Note which channel had the higher SWR? If the SWR is higher on channel 40, you need to shorten the tip. If the SWR was higher on channel 1, you need to lengthen the tip. Move it about 1/4" at a time or screw it out longer a turn or two at a time. Most antennas have a set screw you can loosen so that the tip can slide up and down. If this does not give enough adjustment, you can clip or file 1/4" at a time off the bottom of the tip and reinsert it in the coil. Make sure you put the cap(s) back on if the antenna came with one and to reset the SWR meter every time you take a reading.
If you're using twins, make equal adjustments to each side at the same time. If the SWR is in the red, do not keep the microphone keyed. This will protect the final transistors from burnout.
Note: Do not check the SWR when you are next to a metal building or other trucks as this will interfere with the readings you will get.
I hope this has given you a little understanding on the ins and outs of antenna installation.
There are other tips I could go into but this has gotten too long as it is .
Last edited by cb_repairman; 10-29-2008 at 01:58 AM.
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