Installing A CB Radio

Hello there, basic RF install rules dictate that the rig be directly connected to the 12 volt battery. This way you are assured that the tansmitter will get the Amperage it needs to produce the rated RF output. It may take a little effort to get the power lines, BOTH, Ground and +12.. do not rely on chassis ground, to the battery, but it will be worth the effort.

What kind of antenna are you gong to use, Magmount ?, or a permanent system. Now is the time to plan the coax run also!!!

Good Luck!!

 

Hi John,

Before you go to the trouble of installing your radio, I highly suggest that you set it up in the car on a temp basis with a temp antenna, and see how much noise the Prius produces at 27 MHz. That might help you to conclude whether it is feasible to put the effort into a permanent installation.

 

CB Radio? I seem to recall something about that from the late Paleolithic era of radios.

Tom

 

Patrick, as usual, brings up a VERY good point.
I agree, TEST IT OUT before you install it!!!

 

I've been thinking about installing my old Texas Ranger. I was thinking of putting in dual antennas mounted some how under the bumper with some sort of brace that comes out to the back or slightly to the side so as not to interfere with using the hatch. I'm not sure where the best place to mount the actual CB radio is either. Just an idea I was kicking around.

 

Here is a GREAT tutorial on antenna placement and its effects!! Its a little long, put well written..

[FONT=Arial, Helvetica, sans-serif] Mobile Antennas[/FONT] [FONT=Arial, Helvetica, sans-serif] This is an area of hot competition among antenna manufactures. I am not going to cover how to mount your mobile antenna (Radio Shack sells everything you need to mount antennas), but the basic mobile antenna designs that most mobile antennas manufactures are using today. If you have just started reading my page and are new to antennas, you are going to be confused. You cannot just jump right into putting together an antenna without learning a few things about them first. You have to read "Antennas Basics", "Coax Basics" and the "Verticals" sections first before you tackle this section. First we need to introduce a new term that we will be using to rate mobile antennas (gain really isn't a good thing to use, since mobile antennas generally have no gain), "antenna efficiency". This is how well the antenna converts your power (watts) to signal instead of wasting it as heat. An efficient antenna puts most of the power out as signal, so the range of 95-99% is a perfectly efficient radiator (all antennas waste some power, none are 100% efficient). Most base station antennas are 95-99% efficient. Say you are using 100 watts, and your antenna converts 95 watts to signal and turns the remaining 5 watts into heat, this is a 95% efficient antenna. [/FONT]
[FONT=Arial, Helvetica, sans-serif] The most efficient mobile antenna is the 102" whip. If you desire the best performance, the 102" (quarter wave) whip is the only way to go. If you look back to the "Verticals" section and look at the ground plane (figure 1 in "Verticals" section) you can see the main vertical element is basically a 102" whip. The center wire connects to this part. It must be insulated from the vehicle body. This is usually accomplished by a plastic washer. Now, the vehicle body acts as the ground plane, or like the radials on the ground plane antenna! The feedpoint impedance of the 102" whip when mounted on most vehicles is 40 Ohms, so the lowest SWR you can get is 1:3:1. When you assemble this antennas system, if the SWR is above 3:1 on all the 40 channels, then you have a bad connection somewhere. If your coax is ok (see "Coax Basics" section) then you probably have a short or open circuit on your connection to the whip. Check the connections with an Ohm meter, center pin of radio side of coax should have an electrical connection to the actual whip and not the body of the vechicle, and the collar of the radio side of the coax should have an electrical connection to the body of the vehicle and not the whip itself. Make sure your assembly is right. If everything is assembled right, you should see an SWR 2:1 and lower (down to about 1:2:1) over the 40 channels. Really, your whip should not need adjustment, so before you think about "pruning" it, you better check to make sure things are working right. Do not let the 2:1 SWR fool you, getting it down to 1:2:1 will not get you much more (if any) performance! The only exception to pruning your whip is if you intend on talking above channel 40. If you use, lets say 27.555MHz, then you will need to trim a few inches off the tip of the antenna. Start by trimming a 1/4 of an inch off at a time and rechecking until your SWR is where you want it.If you need to lengthen the antenna, you can do so by added a spring or quick-disconnect fitting which will add around 2 - 4" to the overall height. This should get you well below channel 1 with a low SWR. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Most of us do not have room to use a 102" whip on our vehicle. Plenty of manufactures make a shortened antenna for our use. How do they do that? Simple, somewhere on the antenna (the base, center, top or entire antenna) they wind a coil to compensate for the length that they are shortening the antenna from 102". So if your mobile antenna is 54 inches, the manufacture has made a coil to compensate for the 48" inches they are short from 102" (102 - 54 = 48). When a coil is added to an antenna it does three things. One, it cuts down on the antenna's efficiency. Second, it cuts down on the bandwidth. Third it cuts down the antennas impedance (it lowers it even more than 40 Ohms). The shorter the antenna is made, the more these three factors are reduced. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Extremely short antennas are to be avoided at all costs. There are differences in efficiency between the different methods of "loading" (placing a coil on the antenna to compensate for shortening it) a mobile antenna. The four types of loading are base, center, top and continuous loading. Figure 1 shows the four types of loading. [/FONT]
[FONT=Arial, Helvetica, sans-serif] [/FONT]
[FONT=Arial, Helvetica, sans-serif] Figure 1 - The four different ways to load a shortened mobile antenna. The first three are usually have stainless steel shafts whereas the last one is usually wrapped on a fiberglass rod. That is then covered with a plastic weatherproof covering. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Their performance can be summarized like this. If these antennas are all the same length (say 54 inches) the least efficient antenna is the base loaded whip. Its advantage is that you can make a heavy coil that will have a higher power handling capability than a center loaded or top loaded mobile antenna. A thicker coil handles more wattage, but you could not have a heavy coil in the middle of the antenna or top because the antenna would not be able to support it (it would be too "top heavy"). But still, it is the least efficient of all the shortened antenna types. For improved antenna efficiency, you could use the center or top loaded antenna. The center and top loaded antennas have about the same efficiency, so there really is no difference. You will mainly find only center loaded antenna however. Top loaded antennas are rare because they are more difficult to make strong enough to support the wind load. The most efficient of the shorten mobile antennas is the continuously loaded mobile antenna. It is usually a fiberglass rod wrapped up its whole length with a copper wire or flat ribbon. Use it when you must use a shortened antennas and want maximum performance. Use the longest possible for your vehicle. Its only disadvantage is it usually cannot handle high power (like over 500 watts) because it has to wrapped with a thin wire so its flexible and light. [/FONT]
[FONT=Arial, Helvetica, sans-serif] A glance at the different mobile antennas for sale results in extreme buying confusion. First and foremost, the mounting location is the most important aspect to performance. You must get as much of the antenna over the top of the vehicle as you can. Roof mounting is most desirable, followed by trunk deck / hood mounting then lastly bumper mounting. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Most fiberglass whip makers are claiming their antennas are 1/2 wave, 3/8 wave, 5/8 wave and 3/4 wave antennas. That sounds very impressive. But is it electrically true? Yes, the makers of these antenna wind the respective length of wire onto the fiberglass antenna but does the radiation pattern benefit from the extra wire length as claimed? In a nutshell, no. The extra length of wire (beyond 102" inches) is coiled so closely together to be able to actually fit on a skinny fiberglass rod that it electrically ends up performing the same as the 1/4 wave antenna. There are some exagerated claims of performance from some companies. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Luckily, the performance difference between different makers is so minimal it almost better to pick antennas based on the antenna you like the looks of most! [/FONT]
[FONT=Arial, Helvetica, sans-serif] Radiation Pattern of Mobile Antennas[/FONT]
[FONT=Arial, Helvetica, sans-serif] Most people think that antennas mounted on vehicles are omnidirectional. This is mostly true, but the radiation pattern is influenced greatly by the body of the vehicle. Remember we stated that the body acts as the "radials" for the antenna? Well, we know that the body does not extend around the base on the antenna equally. Figure 2 shows how the radiation pattern of a whip is influenced by the body of the vehicle. As you can see, the shape of the pattern depends on where you mount the antenna. The pattern is "pulled" to areas where there is the most vehicle body. The pattern is the worst in directions where there is no metal body for a radial. [/FONT]
[FONT=Arial, Helvetica, sans-serif] [/FONT]
[FONT=Arial, Helvetica, sans-serif] Figure 2 - The dashed line shows a omnidirectional pattern you would expect from a mobile antenna, but as you can see, the pattern gets distorted from the car body not being even around the base of the antenna. This is why you should try to mount the antenna as close to the center of the vehicle as possible unless you desire a pattern that stresses a certain direction. Do not think of this as gain in a certain direction, this effect is actually detrimental to the overall effiencieny of the antenna. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Co-Phasing Your Mobile Antennas ("Twin Truckers") [/FONT]
[FONT=Arial, Helvetica, sans-serif] Co-Phasing antennas simply means taking two identical antennas, mounting them on the vehicle and feeding them in-phase. One of the biggest misconception of radio operators is what kind of effect this has on the radiation pattern. Most people think that after you Co-Phase two mobile antennas, your signal will be strongest in line with the vehicle body (meaning the signal is strongest down the road straight in front of you and straight behind you also. This is the theoretical effect that you would get from co-phasing two omnidirectional antennas. However, to realize this effect you need to satisfy a couple of requirements. For one, a good earth ground with long (over a wavelength or so) radial wires is required. Secondly, at CB frequencies the closest you would be able to place these antennas are about 18 feet apart. Since it is impossible to satisfy these requirements, the effect of co-phasing is seriously diminished. Unfortunately, even the "Radio Shack Antenna Book" states that co-phasing two mobile antennas will produce a two directional signal. [/FONT]
[FONT=Arial, Helvetica, sans-serif] So then, is there any advantage to co-phasing two mobile antennas? Why yes, there is. Before we noted that the radiation pattern of a single antenna is "pulled" where there is the most metal vehicle body. You can see the pattern is not perfectly omnidirectional like we would expect it be. As we travel down the road, you will notice signal fade ("flutter" or "waver") from this uneven radiation pattern. Co-phasing two antennas will even out the pattern irregularities. Instead of making the pattern more two directional, it will make it more omnidirectional. Do not expect more "gain" from two antennas. Figure 3 shows how co-phased antennas clean up the radiation pattern. Read the section "Co-Phasing" for instructions on how to make a harness to feed your co-phased antennas. It best to get them as far apart as possible. The best way would be to mount one on the front bumper in the center and one on the back bumper in the center also. Most people think this looks silly (me included!) and mount one on each side of the vehicle. [/FONT]
[FONT=Arial, Helvetica, sans-serif] [/FONT]
[FONT=Arial, Helvetica, sans-serif] Figure 3 - Radiation pattern of Co-Phased antennas. The pattern is now more consistent in every direction, and is less influenced by the body of the vehicle. [/FONT]

 

I have used a 50W radio on both CW and SSB (14, 21, 28MHZ) from the 06 prius. The antenna is a loaded whip magmount right at the center of the roof, I didn't want to drill any holes. Now please keep in mind that even though you have a direct connection to the 12V battery, the most current you can draw is 10A (for very short times), ie:10A X 12V=120W maximum, when including the effeciency of the transmitter you are more like 50-75W for short periods. This restraint is even more pronounced when the car is off and you're pulling out of a motorcycle sized battery only now. When the car is on and ready the HV system is charging the battery, you could get a DTC from the computers when pulling more than 10A out of any 12V outlet or even the direct connect to battery. I have since removed the radio equipment and now only use a handheld vhf radio from the prius..Better safe than sorry.

 

I don't recall the last time I saw a CB radio

 

I hear that many folks (illegally) simply mod their amateur radios to use 27mhz. That way, they not only get the chicken bands and 5mhz, they get the whole shebang ... 1800khz all the way (by example, in a Kenwood 2000) up through 1.2ghz. Crush a couple diods, and Voilà !! ... er ... so they say.

You no longer have to dx at 13wpm for a general class license, like back in the 1990's ... you can simply memorize the entire exam pool in a couple week ends ... then your good to go (plus $2K for the Kenwood). You'll have most all the spectrum, minus 900mhz and 220. Pick up those bands if they're "must have", by modding a 900mhz Johnson commercial, and 220 via a transverter. You'll have the ultimate geek mobile ... of course no one will be caught dead, driving around with you. On the bright side, you'll be able to talk more than just 30 or 40 miles cb style (conditions permitting). On the other hand, there's a sweet "jail break" for the i-phone that'll let you transmitt right onto the I.R.L.P. ... which will let you communicate anywhere in the world without geek'ing your car up. Lot cheaper too. Plus you don't have to worry about sucking the life out of your puny aux battery.

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Saw an old CRX towing a utility trailer out of Lowe's today, which was odd enough alone, but they also had a monster tall whip on the roof. Made it look like a full scale RC car. People around here do the darnedest things with their vehicles.

- D

 

Thread resurrection. So did anyone successfully ran a two way communication radio on a maximum of 12 amp load when running even if it calls for adding an extra battery just to support a 20-30 minute continuous radio transmission while the car running. I really need to install a GMRS radio in my car. Thanks,