Radio and Antenna Basics
11-16-2010, 06:03 AM
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Radio and Antenna Basics
Throughout my search for other peoples ham radio or CB radio installation locations, I've noticed many many misconceptions involving antennas and just radio in general. So I figured I would start a thread of basic antenna theory, and also get some feedback on other peoples rigs/gear.
I'm a Ham radio operator (KF7FPH), Electrical Engineering student, and truck driver. I've had my experience with radios for a while and have a decent understanding of how they work fundamentally. With proper install considerations and tuning. Most CBs will transmit 5 or more miles in a state like MI, lots of rolling hills and trees. On my rigs I've been known to keep in contact with other trucks for 12miles...and I had the shortest firesticks on the market.
For good CB performance, the number one most important piece of equipment you have is your antenna. This is for 2 reasons. CB falls in the HF band, also the FCC limits the power to something like 5W, so if you have even just a couple dB of attenuation your ability to transmit any significant distance drops dramatically. I could go into detail on modulation improvements, peak power vs. RMS, tuning etc. But not worth it here. For lack of a better way, I shall just bullet point some common issues/misconceptions, general ideas to follow.
- Dual antennas are NOT always better. Dual antennas give you a couple of dBi of gain in front of your vehicle and in the rear. They also attenuate signals coming from the sides. In the KW I drove this made sense to have dual antennas b/c I mostly used it for highway. For off highway or 4x4 use, a single antenna will offer equal propagation all around.
- For those of you who do want dual antennas, referred to as co-phased antennas, keep in mind these things.
1. Because you will be changing the overall impedance of the system you must use a different coax than before of a specific tuned length, or use a variety of methods using tuned lengths of 75 ohms to connect to your radio. Your needs a 50Ohm impedance to transmit at max power. I can't remember and dont feel like doing math to remember how much of a difference it makes, but not only can it burn up your radio if its really bad, the performance lost is just horrible. The lengths required depend on coax relative velocity and other things. Best off just buying co-phasing kit.
2. The other crucial thing to remember is that separation distance. In general 6 to 7 feet will improve gain from side to side on vehicle and 8 to 9 is where you get gain for front to back. Anything else renders your dual antennas useless and even worse off in many instances than a single.
- The best place to mount your CB antenna apart from height restrictions is the roof. In fact it really isn't that hard to do. Many people are intimidated by a roof install and it really is no different than running your coax through a variety of other places. Bed mounts and bumper mounts can be the worst, unless most of the antenna element is above the ground plane (anything metal on the vehicle). On firesticks they put most of the coil near the top, which helps DRAMATICALLY when considering this. Base loaded antennas however are completely different ball game and almost always have to be on or darn close to the highest metal point in the vehicle.
- Make sure your antenna has a good ground plane. I say this although it may seem obvious it can be tricky. One... corrosion between various parts in vehicles, Two...after a year or 2 depending on mount location and material and vehicle material grades of metal etc. You will find yourself needing to do some maintinence. Especially if mount material differs from the vehicle material at that point. Generally in the form of a quick sand paper job to remove corossion accelerated from the AC current you get from a radio antenna. Again I could go into physics of it/chemistry, but bottom line, corrosion at any place with differing materials including connectors will eventually have to be addressed, especially if you actually use your radio frequently. A way to slow this is use a special oil/coating for radio components. Just a quick dip before install and the lifespan of your install will be significantly improved. I can't remember for certain, the first time I heard of this I was told it was a dielectric material, but from my understanding of physics this would be more of a problem.
- Every rig will be slightly different, and on an HF radio, especially CB where power is low, tuning your SWR is EXTREMELY important. Otherwise you are creating another source of attenuation. Due to the nature of HF radios many people would be surprised what stupid things are causing SWR to be different. Also because every rig is different, antenna mfgrs ship there antennas with a little extra wire on it, in order to "play it safe" instead of sending somebody an antenna that they wont be able to match to there system at all. Again if you want details on WHY its a big deal, I can give you numbers but right now I'm just to lazy to do the math.
- Mag mounts, glass mounts, and other such mounts with the exception of no ground plane mounts and matched no ground plane antennas, are your worst bet as far as performance. Mag mounts rely on magnetic induction for your ground plane, but this varies again from vehicle to vehicle and is nowhere near the same as a good connection.
- A good ground plane is extremely important as well. It needs to have as large of a footprint as possible, for example roof compared to the rail on a bed. Now yes the whole truck actually creates the ground plane in this instance, but the idea is that where you mount is located, the greater the area of the surface around it the better. What we are essentially trying to do is create a near-field reflection point. It is also in part responsible for creating your overall 50 Ohm impedance. There are many No-ground plane mounts on the market, but be sure to pay attention to how they work. Some require a no ground plane antenna that either uses slightly different design to create a 50ohm impedance system, and others are for use with a regular antenna, but sometimes have a T connection somewhere down the coax at a specific distance (yes do not trim), for you to attach a grounding lug or bolt to your vehicle. Keep in mind this grounding location will also have the corrosion issue. So place it in a location you wont mind getting at in a year or 2.
- Unless your doing cophased in which you require either tuned lengths of 75Ohm impedance to the antennas and share a connector at the radio etc. Keep in mind there is more than one way to match impedance for co-phased. Anyways bottom line, make sure your using 50 OHm coax. NOT the same as tv coax. Also again because low power, and the band CB operates in. Cheap coax will make a notable difference in the range you can reach with a CB
- CB tuning is great...but completely useless unless you have a good system. and I've even heard of people burning up their tuned CBs with a poor SWR magmount antenna after transferring their CB from another rig.
- I'm saying it again, the best thing you can do to make sure performance is nominal. USE AN SWR METER. If you don't have one. You can get a power meter/swr at radio shack or at a truck stop. Anywhere from $30 to $60. OR, look for a local CB shop and just have them tune it for a fee. If you can't find one, and your propogation is good enough, park near a highway (not on) and call out on 19 for anybody who might know of one in the area. If you are spending any money on improving your setup. This should be a priority. My first rig was $100 of used parts all said and done. Cheap coax, cheap antennas, cheap CB, cheap mic. The only thing I had going for me was proper co-phase mounts integrated on the KW I drove. My rig was outperforming several $500 setups, with tuned CBs. One guy I was speaking to was desperate for a SWR meter. He had an amp (a.k.a. illegal power boosting box), and was up to 15W and was reaching about as far as I was. If you are going to get a CB, include this in your cost.
- Now I'm sure I'm forgetting many things, or lacking explanation in some areas, but please post your questions.
- For the Hams out there, much of this is a different story. A 2m band 1/4 wave or 5/8whip for example will sometimes include a tuning "chart" for triming the antenna to desired tuning, and for most cases this is more than enough. One due to the nature of being a higher frequency the antennas have much broader bandwidth, and most of us are running 50W or more, (65 personally). Good mounting spot still important, not as much a worry on low loss coax, or with antenna tuning with a SWR meter. Many HAM radios will auto turn the power down if impedance doesn't match or SWR is to high. Don't get me wrong, coax quality, and SWR can severely reduce performance of rig, but its much easier to get swr in a ballpark range (say less than 2) without a specific meter.
Hopefully this clears some misconceptions and for some people, causes more questions to be asked when people are selecting a rig. I may redo this post with much more detail, and better editing or revising to make a clear guide. To reiterate my self once again, mounting point, SWR, and matching impedance can make all the difference in the world with a rig. There are so many people that have had a CB for a while, and never realized they were limiting themselves to 10% of the range they could've had.
For existing dual antennas ask yourself these questions
-----Dual antennas may look cool, but are they useful for you? Do you even have them connected and spaced properly such that you aren't hurting your performance? ---------------------
I'm a Ham radio operator (KF7FPH), Electrical Engineering student, and truck driver. I've had my experience with radios for a while and have a decent understanding of how they work fundamentally. With proper install considerations and tuning. Most CBs will transmit 5 or more miles in a state like MI, lots of rolling hills and trees. On my rigs I've been known to keep in contact with other trucks for 12miles...and I had the shortest firesticks on the market.
For good CB performance, the number one most important piece of equipment you have is your antenna. This is for 2 reasons. CB falls in the HF band, also the FCC limits the power to something like 5W, so if you have even just a couple dB of attenuation your ability to transmit any significant distance drops dramatically. I could go into detail on modulation improvements, peak power vs. RMS, tuning etc. But not worth it here. For lack of a better way, I shall just bullet point some common issues/misconceptions, general ideas to follow.
- Dual antennas are NOT always better. Dual antennas give you a couple of dBi of gain in front of your vehicle and in the rear. They also attenuate signals coming from the sides. In the KW I drove this made sense to have dual antennas b/c I mostly used it for highway. For off highway or 4x4 use, a single antenna will offer equal propagation all around.
- For those of you who do want dual antennas, referred to as co-phased antennas, keep in mind these things.
1. Because you will be changing the overall impedance of the system you must use a different coax than before of a specific tuned length, or use a variety of methods using tuned lengths of 75 ohms to connect to your radio. Your needs a 50Ohm impedance to transmit at max power. I can't remember and dont feel like doing math to remember how much of a difference it makes, but not only can it burn up your radio if its really bad, the performance lost is just horrible. The lengths required depend on coax relative velocity and other things. Best off just buying co-phasing kit.
2. The other crucial thing to remember is that separation distance. In general 6 to 7 feet will improve gain from side to side on vehicle and 8 to 9 is where you get gain for front to back. Anything else renders your dual antennas useless and even worse off in many instances than a single.
- The best place to mount your CB antenna apart from height restrictions is the roof. In fact it really isn't that hard to do. Many people are intimidated by a roof install and it really is no different than running your coax through a variety of other places. Bed mounts and bumper mounts can be the worst, unless most of the antenna element is above the ground plane (anything metal on the vehicle). On firesticks they put most of the coil near the top, which helps DRAMATICALLY when considering this. Base loaded antennas however are completely different ball game and almost always have to be on or darn close to the highest metal point in the vehicle.
- Make sure your antenna has a good ground plane. I say this although it may seem obvious it can be tricky. One... corrosion between various parts in vehicles, Two...after a year or 2 depending on mount location and material and vehicle material grades of metal etc. You will find yourself needing to do some maintinence. Especially if mount material differs from the vehicle material at that point. Generally in the form of a quick sand paper job to remove corossion accelerated from the AC current you get from a radio antenna. Again I could go into physics of it/chemistry, but bottom line, corrosion at any place with differing materials including connectors will eventually have to be addressed, especially if you actually use your radio frequently. A way to slow this is use a special oil/coating for radio components. Just a quick dip before install and the lifespan of your install will be significantly improved. I can't remember for certain, the first time I heard of this I was told it was a dielectric material, but from my understanding of physics this would be more of a problem.
- Every rig will be slightly different, and on an HF radio, especially CB where power is low, tuning your SWR is EXTREMELY important. Otherwise you are creating another source of attenuation. Due to the nature of HF radios many people would be surprised what stupid things are causing SWR to be different. Also because every rig is different, antenna mfgrs ship there antennas with a little extra wire on it, in order to "play it safe" instead of sending somebody an antenna that they wont be able to match to there system at all. Again if you want details on WHY its a big deal, I can give you numbers but right now I'm just to lazy to do the math.
- Mag mounts, glass mounts, and other such mounts with the exception of no ground plane mounts and matched no ground plane antennas, are your worst bet as far as performance. Mag mounts rely on magnetic induction for your ground plane, but this varies again from vehicle to vehicle and is nowhere near the same as a good connection.
- A good ground plane is extremely important as well. It needs to have as large of a footprint as possible, for example roof compared to the rail on a bed. Now yes the whole truck actually creates the ground plane in this instance, but the idea is that where you mount is located, the greater the area of the surface around it the better. What we are essentially trying to do is create a near-field reflection point. It is also in part responsible for creating your overall 50 Ohm impedance. There are many No-ground plane mounts on the market, but be sure to pay attention to how they work. Some require a no ground plane antenna that either uses slightly different design to create a 50ohm impedance system, and others are for use with a regular antenna, but sometimes have a T connection somewhere down the coax at a specific distance (yes do not trim), for you to attach a grounding lug or bolt to your vehicle. Keep in mind this grounding location will also have the corrosion issue. So place it in a location you wont mind getting at in a year or 2.
- Unless your doing cophased in which you require either tuned lengths of 75Ohm impedance to the antennas and share a connector at the radio etc. Keep in mind there is more than one way to match impedance for co-phased. Anyways bottom line, make sure your using 50 OHm coax. NOT the same as tv coax. Also again because low power, and the band CB operates in. Cheap coax will make a notable difference in the range you can reach with a CB
- CB tuning is great...but completely useless unless you have a good system. and I've even heard of people burning up their tuned CBs with a poor SWR magmount antenna after transferring their CB from another rig.
- I'm saying it again, the best thing you can do to make sure performance is nominal. USE AN SWR METER. If you don't have one. You can get a power meter/swr at radio shack or at a truck stop. Anywhere from $30 to $60. OR, look for a local CB shop and just have them tune it for a fee. If you can't find one, and your propogation is good enough, park near a highway (not on) and call out on 19 for anybody who might know of one in the area. If you are spending any money on improving your setup. This should be a priority. My first rig was $100 of used parts all said and done. Cheap coax, cheap antennas, cheap CB, cheap mic. The only thing I had going for me was proper co-phase mounts integrated on the KW I drove. My rig was outperforming several $500 setups, with tuned CBs. One guy I was speaking to was desperate for a SWR meter. He had an amp (a.k.a. illegal power boosting box), and was up to 15W and was reaching about as far as I was. If you are going to get a CB, include this in your cost.
- Now I'm sure I'm forgetting many things, or lacking explanation in some areas, but please post your questions.
- For the Hams out there, much of this is a different story. A 2m band 1/4 wave or 5/8whip for example will sometimes include a tuning "chart" for triming the antenna to desired tuning, and for most cases this is more than enough. One due to the nature of being a higher frequency the antennas have much broader bandwidth, and most of us are running 50W or more, (65 personally). Good mounting spot still important, not as much a worry on low loss coax, or with antenna tuning with a SWR meter. Many HAM radios will auto turn the power down if impedance doesn't match or SWR is to high. Don't get me wrong, coax quality, and SWR can severely reduce performance of rig, but its much easier to get swr in a ballpark range (say less than 2) without a specific meter.
Hopefully this clears some misconceptions and for some people, causes more questions to be asked when people are selecting a rig. I may redo this post with much more detail, and better editing or revising to make a clear guide. To reiterate my self once again, mounting point, SWR, and matching impedance can make all the difference in the world with a rig. There are so many people that have had a CB for a while, and never realized they were limiting themselves to 10% of the range they could've had.
For existing dual antennas ask yourself these questions
-----Dual antennas may look cool, but are they useful for you? Do you even have them connected and spaced properly such that you aren't hurting your performance? ---------------------
11-16-2010, 09:56 AM
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11-16-2010, 11:10 AM
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They are a wilson 48" fiberglass flex 305-4FD picked them up from a local truck stop. 
Not sure if it's tuned exactly for FM or not, but it works, however i know these are: http://www.wearecb.com/store/firesti...nna-p-212.html
or if you want to run just one for both you get one of these: http://www.firestik.com/Catalog/AR-1A.htm
Not sure if it's tuned exactly for FM or not, but it works, however i know these are: http://www.wearecb.com/store/firesti...nna-p-212.html
or if you want to run just one for both you get one of these: http://www.firestik.com/Catalog/AR-1A.htm
Last edited by xxxtreme22r; 11-16-2010 at 11:13 AM.
11-19-2010, 11:43 PM
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so my buddy just went up to reno and his grandpa gave him 2 cb radios. one for him and one for his buddy. well im the buddy 
and i cant wait to put this thing in so your thread was the first one i looked at for my research. any suggestions as to what antenna i should use? just trying to get 5 or so miles of range. nothing huge. any help is great thanks for your time 
and i cant wait to put this thing in so your thread was the first one i looked at for my research. any suggestions as to what antenna i should use? just trying to get 5 or so miles of range. nothing huge. any help is great thanks for your time
12-05-2010, 06:31 AM
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depends on what you use your rig for and whether or not you want something permanently mounted or not.
if you need to go under trees, into parking garages, drive-thrus, etc... then a permanently mounted fiberglass antenna that sticks up way above your roof might not be the best choice - a mag mount that you can pop off your roof in a second and throw it into the back seat or cargo area might be the way to go.
if you plan on wheeling a lot, keep in mind that some groups discourage use of long whips, since they can bend under trees and snap back into the vehicle behind them or spotters (helps if you keep your distance when wheeling too, but stuff happens).
if you need to go under trees, into parking garages, drive-thrus, etc... then a permanently mounted fiberglass antenna that sticks up way above your roof might not be the best choice - a mag mount that you can pop off your roof in a second and throw it into the back seat or cargo area might be the way to go.
if you plan on wheeling a lot, keep in mind that some groups discourage use of long whips, since they can bend under trees and snap back into the vehicle behind them or spotters (helps if you keep your distance when wheeling too, but stuff happens).
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