You need to know how much your going to talk on the radio. Talking to neighbors, DXing, or just freindly rag-chewing. Also keep in mind about the styles of radio. Size, features and ease of use are probably the 3 most important things to consider. If you want to get started with the basics, a Uniden Pro 510XL, Cobra 25 LTD, or any other simple 40 channel AM radio will do. Now keep in mind that mobile radios will need a power supply to run indoors. The power supply should be anywheres from 5 to 20 amps at 13.8 volts. For a smaller radio, a 5 amp will do fine. You will need a 20-30 amp to run a higher wattage 10-meter radio. If your looking for a better radio with alot more features, try a Cobra 148 GTL or a Uniden Washington Base. These radios will also give you Single Sideband. (SSB) Single Sideband has 2 modes. Upper sideband (USB) and lower sideband (LSB). Sideband has no carrier signal so its all modulation. Alot of CBers use SSB for long range contacts and also to get away from noise on AM. Many also buy 10-meter Ham Radios and have them modified to 27 mhz, so that they can talk louder and farther than regular CBs.
Choosing your antenna
There are many different styles of antennas as there are radios. Take time and do some research into what kind your looking for. Your antenna is 90% of your set-up. If you have a really good radio and a bad antenna, your notgoing to do as well. I've hear people with little radios and killer antennas that blows away someone with a $300 set-up. Just because of the antenna. If your going with a base antenna, I suggest a A99 made by Solarcom. This is a widely used antenna thats been around for years. Plus, its adjustable at the base for matching to just about any CB radio. (Do not use a mobile antenna for a base antenna!) If your looking for a mobile antenna, I suggest a magnet mount antenna to get you started. Any antenna from your local Radio Shack will do, but if you want performance and quality, try a Wilson "Little Wil" or 500 model. These antennas are quite popular. So are the K-40 brand. Now, with the mobile antennas, you'll have to match the radio with the antenna. This is done with a SWR meter. (Standing Wave Ratio) Some people ask me or tell me that a SWR meter is not important. Well....these are the same people who come back with their radios burned up. A SWR meter will tell you if you have any shorts or mismatch with the antenna. You don't need to purchase one, just borrow one from a friend. Its only hooked up temperaly in between the radio and antenna just for tuning. Some people run it inline all the time and check it every so often. Some radios have this SWR meter in them. Use a calibraited external SWR meter for tuning and then use the SWR meter in the radio to identify serious antenna problems.
Base or Mobile?
This is totally your decision. If you don't think you could operate a CB while driving, then don't! I've seen people that can't operate their cell phones without going into the ditch. I've used many different radios in my vehicles for 16 years. Not everybody can do that. It takes experience. Remember to stay in your vehicle when transmitting and never touch your antenna while transmitting. You can burn your hand and/or cause other damage to yourself and others. It only takes 20 watts of RF power to light a light bulb. If your going to have a base antenna, mount it high enough away from people, electrical wires, buildings, etc. Depending on the make and design of the antenna, height of the antenna will be different. You can mount a antenna anywheres from 12 to 200 feet from the ground. Read the instructions on the antenna for best results. A Antron 99 antenna works very well between 22 and 78 feet. You will want to use 50 ohm coax to run your base antenna. Do not use TV coax! Its not the same ohm rating. (72 ohms) I use mini 8X coax. This is about the same diameter as RG-58. RG-58 handles 500 watts and mini 8x handles 1000 watts and is made with better materials. Its pretty flexable, but don't crimp, pinch or bend it too sharply around corners. This will affect the coaxs ohms and possibly short it out. Make sure all fittings and connectors are soldered and/or grounded as needed.
Overall Operation
After you have your whole set-up complete, your ready to hit the airwaves. Follow the instructions that come with whatever radio you get. This is my opinion only, but treat people how you expect to be treated over the air
Mic Wiring
Cobra Models:
18ULTRA/LTD, 19/ULTRA/LTD/DXLTD/GTL, 21XLR/GTL/LTD/Classic, 25GTL/LTD/Classic Gold/LTDWX Classic/PLUS, 26, 29XLR/LTD/Classic/WX/ST/PLUS, 31PLUS, 33PLUS, 40X, 77X, 78X, 86XLR, 87GTL, CAM89, 89GTL/XLR, 93LTDWX, 135/XLR, 138XLR, 139XLR, 146GTL, 148GTLDX/GTLB, 1000GTL
Standard:
1-Shield
2-Audio
3-Transmit
4-Receive
Galaxy Models:
2100, 33Plus, DX33HML, Dx44V, DX55, DX66V, DX77HML, DX77V, DX88HML, Jupitor, Mars, Mirage, Mirage 44, Pluto, Saturn, Saturn 2, Sirius, Super Galaxy
Standard:
1-Shield
2-Audio
3-Transmit
4-Receive
Cobra Models:
18RV, 19X, 19PLUS, 20PLUS
Standard:
1-Audio
2-Transmit
3-Not Connected
4-Shield
5-Receive
Cobra Models:
90, 140GTL, 142GTL, 148GTL, 2000GTL, 2010
Standard:
1-Audio
2-Shield
3-Receive
4-Switching Wire
5-Transmit
Mics:
Astatic:
Shield,audio groung
Blue,switching groung
Red,transmit
Black,receive
White,audio
Yellow,not used
Turner:
Sheild,audio ground
Red,switching ground
Blue,transmit
Black,receive
White,audio
Yellow,not used
Sadelta:
Shield,audio ground
Brown,transmit
Green,receive
white,audio
Realistic:
Shield,audio ground
Blue,switching ground
White,audio
Red,transmit
Black,transmit
K40:
Shield,audio ground
Black,switching ground
White, audio
red,transmit
blue,receive
Galaxy:
Shield,audio ground
red,transmit
black,receive
yellow,audio
List of freqs that you might want to avoid using...
Freeband Allocations (25 - 30 Mhz.)
25.020..........U.S. Army
25.035........U.S. Army
25.040........Oil Spills Cleanup
25.069........U.S. Navy
25.080.......U.S. Coast Guard
25.085.......U.S. Navy-Ships
25.090.......U.S. Navy-Ships
25.095.....U.S. Navy-Ships
25.100.....U.S. Navy-Ships
25.105......U.S. Navy-Ships
25.110.........U.S. Navy-Ships
25.111.........U.S. Navy
25.130.........U.S. Air Force
25.161........U.S. Air Force
25.198.........U.S. Air Force
25.230....Inter-Military Freq.
25.240...................................................................U.S. Army
25.245.....U.S. Air Force
25.333...................................................................U.S. Air Force
25.335...................................................................U.S. Marine Corps
25.340...................................................................U.S. Air Force
25.350...................................................................Inter-Military Freq.
25.360...................................................................U.S. Navy
25.365...................................................................Inter-Military Freq.
25.380...................................................................U.S. Coast Guard
25.390...................................................................U.S. Army
25.400...................................................................Inter-Military Freq.
25.410...................................................................U.S. Navy
25.412...................................................................U.S. Navy
25.415...................................................................U.S. Coast Guard
25.425...................................................................U.S. Army
25.430...................................................................U.S. Dept. of Energy
25.440...................................................................U.S. Navy
25.450...................................................................U.S. Army
25.470...................................................................U.S. Navy/Air Force
25.480...................................................................U.S. Navy
25.515...................................................................U.S. Navy/Air Force
25.525...................................................................U.S. Air Force
25.535...................................................................U.S. Army
25.550...................................................................U.S. Army
25.575...................................................................U.S. Navy
25.590...................................................................U.S. Navy
25.597...................................................................U.S. Air Force
25.845...................................................................U.S. Marine Corps
26.110...................................................................U.S. Navy
26.310...................................................................U.S. Navy
26.356...................................................................U.S. Air Force
26.389...................................................................U.S. Air Force
26.485......U.S. Navy
26.490.......U.S. Navy
26.500.......Inter-Military Freq.
26.510.......U.S. Army
26.515.......U.S. Navy
26.540.......U.S. Navy
26.550.......Inter-Military Freq.
26.560.........U.S. Navy
26.575.........U.S. Army
26.580........U.S. Navy
26.590.........U.S. Air Force
26.610...................................................................U.S. Navy/Marine Corps
26.615...................................................................U.S. Navy
26.620...................................................................Civil Air Patrol
26.625...................................................................U.S. Air Force
26.630...................................................................U.S. Army
26.650...................................................................U.S. Navy
26.665...................................................................U.S. Navy
26.675...................................................................U.S. Navy
26.684...................................................................U.S. Air Force
26.700...................................................................U.S. Army
26.710...................................................................U.S. Air Force
26.725...................................................................U.S. Marine Corps
26.750...................................................................U.S. Navy/Air Force
26.775...................................................................U.S. Marine Corps
26.800...................................................................Border Patrol
26.825...................................................................U.S. Navy
26.835...................................................................U.S. Navy
26.850...................................................................U.S. Navy/Army
26.875...................................................................U.S. Navy
26.880...................................................................Border Patrol
26.900...................................................................Inter-Military Freq.
26.925......U.S. Navy/Army
26.930.......U.S. Navy/Marine Corps
26.945......Federal Aviation Admin.
27.545........U.S. Navy
27.550....U.S. Navy/Army
27.565.......U.S. Navy/Army
27.575........F.C.C.
27.585.......F.C.C.
27.590........U.S. Coast Guard
27.595.......U.S. Navy
27.600........U.S. Navy/Army
27.615..U.S. Navy
27.625......Federal Aviation Admin.
27.630...........N.A.S.A.
27.650.....U.S. Navy/Army
27.655........U.S. Navy
27.675.......U.S. Army
27.700.......U.S. Navy/Army
27.715.......U.S. Navy
27.725.......N.A.S.A.
27.745....U.S. Navy
27.750......U.S. Navy/Army
27.775.......U.S. Army
27.785.......U.S. Coast Guard
27.794......U.S. Army]
27.800......U.S. Navy/Army
27.825.....U.S. Army
27.850......U.S. Navy/Army
27.870.......U.S. Air Force
27.875......U.S. Army
27.900..........U.S. Army
27.925........U.S. Army
27.950.......U.S. Navy/Army
27.964......U.S. Navy
27.975..........U.S. Army
27.980.........U.S. Coast Guard Reserve
27.995........U.S. Army
28.000 - 29.700......10 Meter Amateur Band
29.895...........U.S. Navy
29.900.....Air Force One
29.905.........Inter-Military Project
START WITH A GOOD ANTENNA
When you are putting together a system for your vehicle,
whether on a budget or not, plan on buying the best antenna
system (coax, mount, antenna stud and antenna) that you can find
and go buy a radio.
WHAT ARE SOME GOOD ANTENNAS?
Antennas have to be designed to transmit and receive on the band that you are using. CB is located in the 11-meter band.(They call it that because the wavelength is about 11 meters.) CB antennas range in height from a little under 2 feet (24 inches) up to 108 inches.
The 1/4 wave whip (108") will offer better reception and transmission capability over a shorter, coiled or "loaded" antenna.
VERY short antennas, or multiple antennas that aren't "phased" properly will result in a very poor signal. Remember, for co-phasing antennas, they must be 1/4 wavelength apart which, for the 11 meter band, is around 9 feet. Most cars aren't wide enough to allow antennas to be placed 9 feet apart. The other characteristic of co-phasing is that it is much more directional- than a single antenna. It will transmit and receive MUCH better along the axis of the car than sideways off the car so if you want a omnidirectional antenna, you don't want co-phasing so you only want one antenna.
Another subject of common questions is about antennas which receive AM/FM broadcast stations and act as a CB transceiver antenna. In general, these antennas work but are not nearly as good as a dedicated CB antenna. You have to weigh the advantages and disadvantages for your circumstances.
Good brands of dedicated CB antennas in the USA include (but are not necessarily limited to Hustler, Wilson, Antenna Specialists, Solarcon, Jo Gunn, FireStick, K-40 and Francis. Some of the home made loading coils are excelent.
WHAT SHOULD I CONSIDER WHEN CHOOSING A LOCATION FOR MY ANTENNA?
The answer to this question differs greatly between base and mobile installations. Each will be answered separately.
In mobile installations, things to consider are whether you're willing to drill holes or want to use a magnet mount, gutter mount, trunk mount, or a bumper mount. If you say no to all of those,which would probably mean you have a very nice car your list of options is pretty short otherwise you can start making choices with the following things in mind:
1) the closer your antenna is to the top & center of the vehicle, the better. So the roof is better than the rain gutter or trunk and all of those are far better than the bumper. But they'll all work.
2) a drilled/permanent mount is better than a magnet mount in the same location. (This is so that the antenna gets a better "ground plane".) If you use a magnet mount, run your coax feed line through the door or hatch that gets the least use and then leave it alone. Don't use any path where the coax would get pinched.
For base installations (i.e. at home) the best places are "as high as you can" within legal limits. The roof is normally fine. If you're in an apartment complex, you may be limited to a balcony but ask the manager - they may just want you to keep it "invisible." (Check your national and local regulations. In the USA, the FCC regulations limit CB antennas to 60 feet above ground level or 20 feet above the tallest structure on your building. Maybe shorter if you live close to an airport - one foot high for every hundred feet from the nearest runway.)
Base station antennas should have a good ground in case of lightning. (In the rare event of a lightning strike, this can mean the difference between burning down the building or just the radio.) Most cold water pipes that go into the ground will work. But the best choice for a ground would be an 8-foot (2.4m) copper rod stuck in the ground near the antenna. (If you want to use anything other than the rod for a ground, contact someone knowledgeable about housing construction and safety - you don't want to accidentally use a hot water or gas pipe. You also need to know your local building codes.
Aside from a bunch of fancy options that do little to improve
the performance of your system, all radios are pretty much the same.
The manufacturing of CB radios is a government-regulated process.
The final output power, by law, is regulated to a maximum of 4 watts.
Some manufactures try to fool you by using words such as "5 Full Watts of Power" I thought that you might like to know what they really mean when they say 5 full watts of power.
This is not a misstatement. Also, it is not the audio they are talking about. The Final RF transistor Collector Voltage is usually figured at 13.8 vdc. With that voltage applied to the Final's Collector, the maximum current that you can set the radio for and still be within the FCC specifications is 362.3 milliamps.
P = E x I
This means that the power that is being consumed by the final RF stage is 13.8v x 362.3 = 5 watts. The final RF stage is usually operated as a high-level modulated class "C" amplifier.
The efficiency of a class "C" amplifier is a maximum of 80% (mathematically provable). 80% of the 5 watts that the RF final consumes from the automobile battery or the A. C. Power Supply is 4 watts.
The folks that advertise 4 watts output power are correct and the ones that advertise a full 5 watts of power are also correct. If anyone is advertising 5 watts of power OUTPUT, then they are lying as there is no 5 watts OUTPUT on transmit unless the radio is operating against the FCC Rules and Regulations.
Of course, there is absolutely nothing wrong with having all of the features, but not if the extra cost means that you are going to skimp on the antenna system. It is a bad trade off and one that is all to often exercised. The best radio with a lousy antenna system will NEVER outperform a cheap radio with a good antenna system. If anyone tries to tell you otherwise … run for the door. Cheap antenna systems are cheap for a reason and that almost always means lousy components throughout.
In many cases, it isn't always just the antenna that is bad. In way too many instances you get a piece of coax that would be best utilized if it were used to tie your dog to a tree. There is a lot of junk cable on the market! If you were watering your yard with a hose that was literally full of holes you would better understand the problem of poor coax cable. Unfortunately, you can't see RF energy pouring out, or interference pouring into a piece of bad coax, but that is what you can often end up with.
Another part to watch for is the stud mount. The stud mount needs to be mechanically strong and electrically superior. Those in the know about electronics, RF or otherwise, will tell you that the majority of problems in an electrical or electrical-mechanical device will involve poor connections that cause opens, shorts or high resistance. The stud mount is an electrical mechanical device that must support the antenna and act as a bridge between the antenna and the coaxial feed to the radio. Again, if you are looking for cheap ones, you can find them. They are made of aluminum, or they use non-stainless steel washers that are sure to corrode, or they have cheap plastic insulators that crack or collapse under normal conditions. And some of them have all of the above!
When you shop, shop smart and you will only need to do it once. Give the majority of your time and money to the antenna system and you will be making the right moves.
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SWR
1 - By definition SWR is the ratio of outgoing power to reflected power. Any power being reflected, is NOT going out of the antenna. A perfect match is ALL wattage going out and NONE reflected back to radio.
How do you figure the coax length? The formula is as follows.
468 divided by Freq. in Mhz. times velocity factor (.66 for Polyethylene, .78 for Foam) will give you the following.
POLYETHYLENE
Channel 1 - 468 -:- 26.9 = 17.397 x .66 = 11.482 or 11'5" x 2 = 23' 0"
Channel 20 - 468 -:- 27.2 = 17.205 (or 206.4") x .66 = 11.355 or 11'3" x 2 = 22' 8"
Channel 40 - 468 -:- 27.4 = 17.080 x .66 = 11.272 or 11'2" x 2 = 22' 6"
FOAM
Channel 1 - 468 -:- 26.9 = 17.397 x .78 = 13.569 or 13'6" x 2 = 27' 0"
Channel 20 - 468 -:- 27.2 = 17.205 (or 206.4") x .78 = 13.419 or 13'5" x 2 = 26' 10"
Channel 40 - 468 -:- 27.4 = 17.080 x .78 = 13.322 or 13'3" x 2 = 26' 6"
The 206.4 inches above is significant in that the Radio Shack whip is 102 inches, many mobil setups can't use the 11 or 13 ft. lengths because it will not reach the radio, so in the real world the best length is 22 ft. or 26 ft which should get the SWR's down.
Now Francis Antennas recommends 18 Ft. that's because it is tuned to that length of coax. I have found this to be a good length for a Francis.
OK, what does that have to do with base station antennas?
A little story here, when I set up my Base Station, I used an Antron 99, I put it on top of a 40 Ft. pushup pole. I used the old standby of 36 Ft. of coax for a full wavelength, I needed more than that so I went to Radio Shack and got 72 Ft. of RG-8 foam coax.
I followed Antron's instructions went to Channel 40 then went to Channel 1 and balanced the 2 readings by adjusting the tuning rings on the Antron, the outcome was 1.5 SWR on both ends and 1.4 on Channel 20.
Next I inserted a 3 Ft. jumper into the line, humm! On Channel 20 the SWR went UP! That meant the coax was too long so I cut 2 Ft. off, SWR came DOWN to 1.2, cut off 2 more Ft. making the total length 68 Ft. SWR came down again to 1.05 to 1, which I can live with. This will work for the Antron 99 which is tunable. Other antennas may be different but the principal is the same.
The fact that the coax was getting shorter shows me that the above figures are good. In the real world, it didn't work out that way. You must make real world adjustments.
NOTE: In a mobil setup, if your SWR is 3, your antenna is not grounded. There is one thing I can't say enough about and that is GROUNDING!! If in doubt Ground it out, especially if you are running power, for antennas mounted on the trunk, you need to ground the trunk with copper straps, like battery straps.
I receive calls from baffled radio users, with the same complaints : "My microphone shocks me when I key up!", "Radio hums on high power or with the amplifier on", "My SWR increases when I turn up the power" or "I have low SWR, but can only talk a half mile". Most of the time these symptoms all point back to the same problem, improperly configured coax cable and RF grounds. This is an especially crucial issue when you are using an amplifier as well.
There are a few common mistakes individuals (and shops) make when installing antenna systems, most are easily remedied. First, and probably the most common; extra coax cable is coiled in a circle or loop.
This is not a good idea as the coil then becomes an extra loading coil, sending RF energy into the cab or other location other than the antenna. This is probably the biggest producer of microphone sparks, and definitely the most painful (speaking from personal experience).
To correct this, try to run the coax differently stretching it out. If you still have excess, make a large figure eight or zigzag pattern. This will offset the magnetic fields, which cause the problem. Second: make sure all PL-259 connections are well soldered, especially the grounding points. Never trust a crimp on connector.
Third: if your antenna is mounted to any moving body part (door, trunk lid) connect a short wire from that part to the body when possible, this will assure a good ground especially in instances where you must contend with weather-stripping and other poor conductors. Following these few simple rules will make installing and tuning your total system much easier, and occasionally, less painful.
CLIPPING THE LIMITER MYTH
For all of you golden screwdrivers out there that think that clipping the limiter is going to make your radio better, "DO NOT DO IT!" Your just going to make your radio exceed 100% modulation, sound distorted and produce all kinds of harmonics.
When you "clip" the limiter, you remove it from the mic input circuit, and in doing so, cause the radio to be very sensitive to RF and causing (squeal).
In some of the earlier radios clipping the limiter was the only way to improve the modulation, and even then, it did not make the radio exceed 100%.
TUNEUP INFORMATION
I have received lots of questions about "how can I tune my radio for more power?" You can't, It takes more than just turning a few pots. Strangely enough, there are many "truck stop hacks" that do just that and call it a "peak and tune" and charge $20.00 to $35.00 to do it.
Well, it takes more than just a few twists to tune up a radio, it takes proper equipment like an accurate Frequency Counter, RF Signal Generator, Oscilloscope, a good VOM (volt/ohm) Meter, a 50 ohm/1000 watt Dummy Load, a good quality RF/SWR Meter and lastly a frequency reference like a receiver that tunes WWV in Ft. Collins Colorado, to calibrate your Frequency Counter.
LIGHTNING AND POWER SURGE PREVENTION
Every month we take in hundreds of repairs for customers, Many of these items are sent in with power input related damage. In particular, on base station amplifiers and radios:
In this tip I will cover the basics of AC spikes, and not the more detailed problem of electrical damage resulting from antenna line spikes, such as caused by lightning. AC line voltage in the US is usually around 110 to 120 volts, as it is supposed to be.
However, due to weather conditions, or line equipment failure, these AC lines can transmit well above the acceptable voltage to your radio or amplifier's power supply circuitry. In most cases, each unit has a built in supply that rectifies 120Volts AC to DC voltage, to be used by the internal circuitry. All RCI and Galaxy base stations are built in such a fashion, as are many others.
These devices normally come with AC circuit-side fuses, and DC circuit-side fuses, some may be internal. This is your last stage or protection, and it is crucial that you used the rated fuses for these devices. To further protect you device, always use the third prong on the devices that come with them, this allows for the case of the device to be grounded to you homes electrical system.
Do not use extension cords that bypass this third prong. To make absolutely certain your expensive equipment is protected, the ideal means is a Personal Computer type UPS system. This rectifies the AC to DC, and back to AC, making it almost impossible to force an electrical spike through this type of device, and it will also allow you to use your radio equipment in the event of a power outage, for a brief period until the internal batteries are depleted. These devices are rather expensive, but are an excellent idea to protect your equipment, and for emergency preparedness.
A less expensive and more easily obtainable protection device is a standard Computer Surge Protector, available at any general merchandise store (such as Wal-Mart). Make sure that you choose one with an Insurance Option; basically theses refund you the price of your equipment if it's damaged by electrical surges, while their product is in use. These are slightly more expensive, but well worth the small investment. Simply fill out the card included with the purchase, and mail it in with the details of your equipment. Combined with proper maintenance, and tuning, your equipment should last through many years of service with the proper electrical filters such as the above.
I am sure you all know this, but just to be on the safe side, when there is a storm its better to be safe then sorry. I disconnect all my equipment. I have seen over the years too many radios, including equipment, linears, antennas, and an entire radio room totally destroyed by lighting.
INTRODUCTION
CB radios are designed to be two-way devices. That is … they receive and they transmit. These are the two primary functions. Both functions share some common circuitry, but they also work independently of one another. We often hear from people that say, "I receive okay but nobody can hear what I’m saying" or "They hear me but I don’t hear them." Because we are an antenna manufacturer either of the two statements are often followed by "Do you think there is something wrong with my antenna setup?"
The radio manufacturers most certainly field technical calls that question the radio’s performance when indeed the problem is antenna related. Likewise, we field numerous calls from individuals that want to fix an "antenna problem" that really isn’t an antenna problem. In this article we will offer our angle on some of the more common problems we run into regarding radio troubles and offer some ways for you to troubleshoot and/or fix the problems.
WIRING POWER TO THE RADIO
This is one of the biggest problem areas we run into when performance problems occur. Do not overlook the 12 volt power line that feeds the radio. Just because the lights come on, do not assume that sufficient power is available. It is our strongest belief that the power to the radio should come directly from the battery. There are several reasons why. First of all … it is what we call "clean power." When you tap into a circuit under the dash there is no telling, short of studying schematics, what other accessories are sharing that circuit. If there happens to be a relay or motor in or near the tapped into circuit, there is a possibility that the radio will pick up "noise" and or realize power drops that could affect performance. Some of the "hardcore" radio operators will use a piece of coax to run power from their battery to the radio. By using the center conductor as the positive lead and the shield as the negative lead, a clean and shielded power source is available. Another advantage of running straight to the battery is that the radio can be used at anytime. You will not need to turn on the ignition switch as would be required on some circuits. In the event of an electrical problem, communication will still be possible.
As a final note on power, make sure you have full battery power available at the radio. It is a very good habit to check the voltage to see that you have 12 to 14 volts available. The fact that the radio lights come on does not mean that you do! We have seen this problem numerous times. LED’s and lamps will light up with as little as 5 volts but your transmitter and receiver will not function properly without full power. Corroded connections, poorly crimped connectors and wire gauges that are too light to carry the needed current are power thieves. Two strands of wire in a 20 strand bundle will give you the false impression that everything is okay but the radio cannot draw enough energy to function as intended. And yes … it will affect receive just as much as it will affect transmit. We recently looked at a problem installation on a motorhome that "wouldn’t receive over 75 yards." The owner tested three different radios and none of them performed better than the other. He assumed the antenna system was at fault even though the SWR was below 1.5:1 on all channels. When we checked the power feed we found less than 7 volts available. As soon as we ran a good line we were talking to people several miles away.
BLOWN TRANSMITTERS
Any condition that causes high SWR has the potential to wipe out the transmitter’s power transistor. If you’re receiving signals but nobody responds back, you may have lost half of your radio. It happens all the time! If you apply the principles of "plug-n-play" or "point-n-click" to a CB installation there is a strong probability that money will leak out of your account. Shorts in the antenna system and/or high SWR will damage your radio. Shorts are the worse! Untuned and untested systems are next. We always recommend that a volt/ohm meter be used on the antenna system BEFORE the coax is ever connected to the radio. Ground-plane dependent and no-ground-plane systems have a different testing procedure and you need to be familiar with the specific characteristics of the type of antenna system you are installing (There are articles on this subject in our library). However … in every case … if you have any continuity between the antenna base and the antenna mount on applications where a feed-through antenna stud mount is being used … you have a problem, and the radio should not be used. And, with the coax disconnected from the radio … if you have any continuity from the antenna base to any ground point on the vehicle, that too indicates a problem.
High SWR caused by untuned antennas will not toast the transmitter during testing. The problem is a time-based one involving heat build up. During SWR testing the transmitter is activated in short bursts. Cooling off time exists between calibration and the collection of the readings. Until all components are tested and the SWR adjusted, you should not keep the microphone "keyed up" for longer than 10 seconds at a time while calibrating and testing … especially if at any point the SWR readings are at or above 3.0:1.
Read all that you can read and go into your installation with knowledge. With so many possibilities it is nearly impossible to answer every question that will crop up, But if you get a grip on the fundamentals, you’ll be well on your way to getting the maximum performance from your 2-way radio.
The popular statement, "There’s good news and bad news ...", could have been written for CB radio. The good news is, sometimes you can talk to someone down the street, or halfway around the world. The bad news is, you may not always be able to talk to someone down the street, or halfway around the world. That is the nature of communications on the CB band.
The frequencies that CB radios operate on are affected by terrain, ambient weather conditions, the forever changing height of the ionosphere, sun spot cycles with their radio frequency (RF) interfering magnetic waves, and the quality and design of the equipment. On any given day (or hour of the day) you might find that the person you spoke with earlier can no longer be contacted. And, while you are trying to talk to that person who is two or three miles away, somebody that lives a thousand miles or more away comes in as if they were in the other room. Since it is humanly impossible to manipulate the things in nature that affect all radio wave transmissions, especially those in the CB band, knowledgeable people with honest intentions will not promise the CB user a specific distance that they can consistently communicate over. Of course, dishonest people are apt to tell you anything when trying to separate you from your hard-earned money.
If ask to make an honest statement regarding the distance that one may expect from a legally operated CB, the statement across the industry must read as follows.
CB operators can expect a fairly consistent operational range of three to five miles in an area of limited obstructions. Prolonged periods of relatively consistent performance between two or more sites in the five to twenty-mile range is a very common occurrence. Consistent operation between locations beyond twenty miles will most often be sporadic. During the course of any given day, for a period that will vary in duration, could occur at any given hour and be in any possible direction, communicating over hundreds, thousands or even tens of thousands of miles with no more than 4 watts is a very probable possibility.
There are many things that a CB operator can do to maximize performance under any set of conditions.
Adjust the SWR
Use high quality coaxial cable
Use top loaded antennas
Use 5/8 wave antennas
Select a longer antenna
Mount antenna higher
Use antenna(s) with proven history of performance
Clean coax and power connections
Make sure other station has quality components
Use in off-peak periods
Use power microphone
Have radio peaked by qualified technician
CB is meant to be a fun, useful, inexpensive, and unlicensed means of communications for Joe Citizen. Cost is minimal and airtime is free. If you are aware of the limitations that go along with the frequency, you can expect your CB to perform exactly as it was intended, so long as you do the most that you can do with the pieces you can control. Have fun! Have good conversations! Have CB!
1. Every industry has its bottom dwellers. We cannot protect you from them. Consumers who make decisions based strictly on price, or on what someone says instead of what they can do, will often fall prey to the bottom dwellers.
2. Beware of information from "experts" (real or self-proclaimed). There is antenna theory and there is antenna reality. We have yet to see a vehicle that simulates a lab. While theory is a good starting place...experience is invaluable when it comes to real problems. The knowledge gained from the best book on theory will not necessarily produce the best antenna design.
3. Some "experts" may "claim" 5/8 wave mobile antennas are not possible because they would need to be 23 feet high. They are wrong! Physical length and ground wave performance are not the same. If you ever hear someone make that claim, ask them how a handheld CB can have a 1/4 wave antenna 8 inches long and mobile 1/4 wave antennas can be anywhere from 12-60 inches long in spite of the fact that a physical 1/4 wave is 108 inches.
4 .Never key up or attempt to operate your CB without a working antenna or "dummy load" (non-radiating antenna simulating device) connected to the radios antenna jack, unless you have extra money to buy another radio, or know a good repairman.
5. All mobile and base transmitting antennas need counter-poise, more commonly called ground plane. The antenna is the reactive unit, the ground plane is the reflective unit. Neither is more important than the other. In mobile installations with standard antenna systems, the vehicle metal (body, frame, etc.) acts as the ground plane. In "no-ground-plane" systems, the coax shield is used for counterpoise.
6. Most, but not all, manufacturers pre-tune their mobile antennas on a test bench. To protect your radio's circuitry and achieve optimum performance, mobile transmitting antennas (CB, cell phone, amateur, etc.) need to be tuned on the vehicle.
7. Before transmitting, you should check your antenna system for shorts or opens. If you have continuity between the center pin of the connector and the outer threaded housing, you may have a short. Don't transmit! If you do not find continuity between the center pin of the coax and the antenna base, you have an open. Fix it. (See "Testing Continuity") Exceptions: Some base loaded antennas use a center tap design and there will be continuity from ground to center conductor. Also, Firestik "No Ground Plane" antenna kits will have coaxial center pin to ground continuity.
8. SWR that pegs the needle on all channels almost always indicates a short in your antenna system. Do not attempt to tune the antenna until the short is fixed. Operating with high SWR will probably damage your CB's internal circuits.
9. Make sure that the antenna you are using is the right antenna for your application. Don't use a TV antenna or an AM/FM antenna for your CB. Do not operate your CB without an antenna or dummy load.
10. Transmitting antennas are sensitive to objects in their "near field of radiation." Tune your antennas in an open area. Never tune inside or next to a building, near or under trees, near or under power lines, and never with a person holding or standing next to the antenna. Try to simulate normal operating conditions.
11. If you mount two or more antennas close to each other, you will alter the transmission patterns of each one. The affect may be either positive or negative. We recommend that a minimum of 12" exist between your CB antenna and other types of antennas.
12. Your radio cannot tell one component from another. As far as the radio is concerned, the coax, stud mount, mounting bracket, antenna and vehicle is ONE unit. Don't be too quick to fault your antenna until you are sure that all of the other components have been given equal consideration.
13. Of all antennas returned to Firestik for warranty service, 75% show no signs of being tuned to the vehicle. All antennas should be checked prior to use. Most will require some adjustment. Less than 3% of all returned antennas have actual performance causing problems. Of those, half of the problems are user or installer created. High SWR and other performance problems are 20 times more likely to be caused by bad coax, bad connections, shorted mounts, poor installation location or faulty test meters.
14. In almost every instance, once you get the same SWR reading on channels 1 and 40, further antenna tuning will not improve the readings. If the SWR is still over 2:1, you have other problems to conquer. Exception: There are rare occasions when the ground plane is so small or large that the system is way out of phase (especially with high-performance antennas). If you have high SWR on all channels and have confirmed that you have no opens or shorts in the feedline, try making a small tuning adjustment in the antenna. There are times when the SWR will drop equally across all channels under unusual ground plane conditions. If you find this to be the case, carefully adjust the antenna.
15. SWR that is high on all channels (over 2:1 but not pegging the needle) after the antenna has been tuned usually indicates insufficient ground plane, ungrounded antenna mount or that a coax cable problem exists.
16. The doors, mirrors, spare tire racks, luggage racks, etc. on many vehicles are insulated from a good ground with nylon or rubber bushings. This also stands true for fiberglass vehicles. Make sure that your antenna mount is grounded, even if it entails running a ground wire to the vehicle chassis. Bad hard ground at the mount generally equates to less than optimum performance. Exception: No ground plane antenna kits do not require a grounded mount.
17. If you are hearing whining noises from your radio while your vehicle is running, it is probably due to "dirty power" being supplied to the radio. Under dash power may be more convenient, but the "cleanest" power will be found by running the radio's power leads straight to the battery.
18. You can never buy coax cable that is too good for your system. Never compromise quality for cost when purchasing coax. Your best bet is to stick with coax that has a stranded center conductor and 90% or higher shielding.
19. Most manufacturers of high performance antennas recommend a specific length of coax cable. If your antenna manufacturer suggests a specific length, give priority to that recommendation.
20. If your ground plane is good, your mount grounded and, your antenna favorably located, coax length rarely becomes an issue. But, if one or more mismatches occur, you may find high SWR. This can often be corrected by using 18 feet lengths of high quality coax.
21. Excess coax between your radio and antenna mount should never be wound into a circular coil of less than 12" in diameter. Doing so can cause system problems. Your best option for handling excess coax is to serpentine the cable into a 12 to 18 inch yarn-like skein. Secure the skein in the center with a wire tie and tuck it away.
22. Single antenna installations require coax with approximately 50 ohm's of resistance (RG-58/U, RG-58 A/U or RG-8X). Dual antenna installations require the use of 72 ohm cable (RG-59/U or RG-59 A/U).
23. Coaxial cables with foam (polyfoam) center conductor insulation should be your last choice for use on mobile (vehicle) installations. Even though it will work initially, it has limited life and does not stand up to the conditions encountered in the mobile environment. Choose coax with polyvinyl insulation when doing mobile installs.
24. Coax cables should never be cut and spliced together like common electrical wire. Line losses will occur.
25. Coaxial cable with holes in the outer insulation, severe bends, or door, trunk or hood caused pinches will cause performance problems. Treat your coax with care.
26. If you live in an area where rain and/or sleet is common, wipe your antenna down with a rag that has been coated with WD-40, Armor-All, Pledge, light oil, etc. This trick prevents ice build up that can overload and cause your antenna to break. In an emergency use butter, cooking oil or anything else that will repel water.
27. When tuning your antenna(s), make sure that you do so with the vehicle doors, hood and trunk closed. If left open, they can cause inaccurate SWR readings. Try to simulate actual operating conditions.
28. Mobile antennas, for best performance, should have no less than 60% of their overall length above the vehicles roof line. For co-phased antennas to perform optimally, the space between the top 60% of the two antennas needs to be unobstructed.
29. Remember, all transmitting antennas need ground plane (counterpoise). Base antennas, much like "no ground plane" antennas, build it in. Do not use mobile antennas for base station applications unless you know how to build your own ground plane.
30. If you are installing a single antenna on one side or the other of your vehicle, best on-the-road performance will be realized if the antenna is on the passenger side of the vehicle (Passenger cars and light trucks) Large trucks or vehicles pulling large trailers should put the antenna on the drivers side to avoid the signal from being blocked by the trailer and to keep from hitting road side trees.
31. Co-phased (dual) antenna installations create a radiation pattern that favors communication directly in front and back of the vehicle. This is why co-phase systems are popular with people who do a lot of highway driving. Co-phase antennas must be center or top loaded. Top loaded antennas are the best.
32. Some people believe that co-phased antennas must be separated by a minimum of nine (9) feet. We have successfully used co-phase antenna systems with spacing as little as four (4) feet. Space alters the pattern and not always negatively. Each vehicle will be different.
33. Co-phase antennas can improve performance on vehicles that lack good ground plane characteristics (fiberglass motorhomes, trucks, etc.). Instead of using available metal to reflect the radiated energy, the antennas use each others field.
34. When tuning co-phased antennas (dual), it is best to adjust both antennas an equal amount to maintain equality in their individual resonant frequency.
35. On a co-phase system, if you try to tune each antenna independently using RG-58 type coax and then connect them to the co-phasing harness, you will almost always find that they will appear electrically short as a set. We recommend that you first assemble the entire system. Take all measurements and make all adjustments with both antennas in place.
36. If you are experiencing SWR that is high across the entire band and have eliminated shorts, opens, groundless mounts and coax as potential problems, suspect lack of ground plane. Try adding a spring or quick disconnect to the antenna base. In some cases, the repositioning of the antenna relevant to available ground plane will solve the problem.
37. One of the greatest benefits of the FS series (patented tunable tip) antenna is noted when there is lack of available ground plane. If the tuning screw reaches its "maximum out" position before satisfactory SWR is realized, a common 1/4-20 threaded bolt or screw of a longer length can be used to replace the supplied tuning screw. If the vinyl cap is too short to remain in place, the user can disregard it or clip a hole in the top for the longer screw to pass through.
38. In rare instances, like antennas mounted in the middle of a metal van roof, excess ground plane can cause a problem. This usually shows up as high SWR across the band. In these cases, a tunable tip antenna may not be the best choice. The reason being, the antenna is too long and the tunable tip cannot adjust down far enough (see line 40). If you suspect this, an antenna that wire can be removed from will usually fit the bill (i.e. KW or RP series).
39. There may be situations when a tunable tip will bottom out before optimum tuning is achieved. If this happens, try removing the knurled jam nut and finger tighten the tuning screw against the o-ring. If still too long, remove the tuning screw altogether. If total removal causes the antenna to go short, cut the tuning screw in half and re-insert it into the tuning extender and re-test. The following items on the FS Series "tunable tip" antennas, when removed, will have an effect on SWR (in order from least effect to most effect). O-ring, jam nut, tuning screw mass (cutting off length), vinyl cap, tuning screw complete.
40. The vinyl cap on any "tunable tip" Firestik antennas is optional. However, your antenna needs to be tuned as it will be used . . . with or without the tip.
41. Magnetic mounts should be used in temporary situations only. If you leave them in the same spot for a long period, the paint will not age like that of the uncovered areas and/or moisture will be trapped between the mount and vehicle causing rust or discoloration. Periodically lift the magnet and gently clean off the underside of the magnet and the vehicle surface.
42. It is a bad idea to use magnetic mounts and amplifiers together. Magnetic mounts rely on capacitance grounding. This situation can literally cause the paint under the mount to bubble or discolor due to excessive heat build up.
43. On wire-wound antennas that require wire removal for tuning purposes, best overall performance will be achieved by keeping the loose end of the wire pressed down tightly against the wire coil. If you use power amplification on top loaded antennas and do not process the end of the wire load so it can dissipate its heat into other adjacent coils, you can melt the tip of the antenna.
44. Generally speaking, center loaded antennas perform better than base loaded antennas, and top loaded antennas perform better than all. For any given antenna design (base, center or top loaded), the taller the antenna the better. With length comes a wider bandwidth (lower SWR over more channels), more power handling capability and overall performance increases.
45. When ultimate mobile performance is desired, function should be given precedence over mounting location convenience and appearance.
46. Don't confuse SWR with overall performance. You should seek SWR of 2:1 or lower on channel 1 and 40, but keep in mind that best performance may not be found at the lowest SWR readings. For the most part, if you get your SWR below 2:1, on both ends of the band, don't be overly concerned about using meter tricking procedures that bleed off energy.
47. The SWR meters built into CB radios are okay for general readings, but are rarely sensitive and/or accurate enough for fine tuning of antennas. Use them mostly to indicate serious high SWR problems only.
48. Firestik has tested literally hundreds of SWR meters. A large percentage of these have shown to be off by 0.3 to 0.7 when compared to a piece of certified equipment. There is no standard among production meters. However, unless a unit is defective, most will indicate the most serious problems that you might encounter
49. Aside from cost, the type of wire used in or on antennas (copper, silver, aluminum, gold, tinned, etc.) has negligible effect on antenna performance. The antenna must be designed to resonate with the wire type and gauge chosen by the designer. However, larger wire gauges will normally increase the bandwidth and heat dissipation abilities of the antenna.
50. Copper is 55% better than aluminum, 27% better than gold and 578% better than tin insofar as conductivity is concerned. Silver will conduct AC/DC current less than 2.5% more efficiently than copper, but the cost to performance is generally unjustified and any gain, insofar as RF transmission is concerned, is negligible.
51. If devices other than an SWR meter are going to be used between the CB radio and antenna, always tune the antenna system first without that device in line. If SWR is high with the other device in line, you will know where the problem is.
52. In "no ground plane" systems, it is best to choose a system that terminates the coaxial ground at the radio end of the cable. These systems are far less reactive to cable routing errors and will almost always outperform systems that are terminated at the antenna base or antenna end of the coax.
53. Cables and antennas from standard & no-ground plane kits are not interchangeable. The "No Ground Plane" antennas from Firestik have a yellow band near the base.
54. Wire wound antennas with a plastic outer coating will greatly reduce audible RF static when compared to metal whip antennas.
55. If you leave your antenna on your vehicle permanently, remove the rubber o-ring that is found on the threaded base of some antennas. Tighten permanent antennas with a wrench. Add a lock washer if you want.
56. If you use mirror mounts and often find yourself in areas with overhead obstructions, tighten the bolts just enough to keep the antenna vertical at highway speeds. If the antenna contacts something overhead, the mount will rotate on the mirror arm and protect your antenna.
57. If you use long antennas and find that they bend too far back at highway speeds, tilt them forward if possible. When under a wind load, they will end up in a relatively vertical position.
58. On antennas that are topped off with a vinyl tip, make sure that you take your SWR measurements with the tip in place. If you tune your antenna with the tip off and then reinstall the tip, your SWR will change.
59. Without advocating the use of power amplifiers or unauthorized channels, take note that the Firestik II tunable tip antennas have a fairly large metal tip that broadens the bandwidth and dissipates a considerable amount of heat.
60. It is illegal to use power amplifiers with CB radios. It is illegal to "tweak" the radios internal circuits to increase output power. The transmitter power of a legal, FCC certified CB radio is 4 watts AM.
61. If having one antenna for CB/AM/FM is appealing, use a CB antenna and a splitter that allows it to be connected to your AM/FM radio. Devices that let you use your AM/FM antenna for CB use will leave you disappointed.
62. On a budget? Buy a cheap radio and a good antenna. Aside from added bells and whistles, all CB's are FCC regulated to transmit no more than 4 watts of power. A good antenna on an inexpensive radio will almost always outperform a bad antenna on an expensive radio.
63. Beware of the wire wound mobile antennas mentioned in ads that claim them to be "full-wave" or "wave and a half". At best, you are being deceived by the misleading association of wire length to actual performance characteristics. Wire length, for all intents and purposes, is irrelevant. With "very" few exceptions, antennas must function as a 1/4 wave or 5/8 wave to be useful on mobile installations. For example, Firestik and Firestik II antennas between 2 foot and 5 foot have a radiation pattern similar to a 5/8 wave reference antenna. However, wire lengths range from 20 feet to 32 feet (0.6 to 0.9 of a full wave length). If wire length was relevant, each antenna would need 22.5 feet of wire.
Police and Fire Radio 10 Codes
10-0 Caution 10-51 Wrecker needed
10-1 Unable to copy - move 10-52 Ambulence needed
10-2 Signal good 10-53 Road block at …
10-3 Stop Transmitting 10-54 Livestock on highway
10-4 Acknowledgement 10-55 Intoxicated driver
10-5 Relay 10-56 Intoxicated pedestrian
10-6 Busy, unless urgent 10-57 Hit and run
10-7 Out of service 10-58 Direct traffic
10-8 In service 10-59 Convoy or escort
10-9 Repeat 10-60 Squad in vicinity
10-10 Fight in progress 10-61 Personnel in area
10-11 Dog case 10-62 Reply to message
10-12 Stand by 10-63 Prepare written copy
10-13 Weather/Road report 10-64 Message for local delivery
10-14 Prowler report 10-65 Net message assignment
10-15 Civil disturbance 10-66 Message cancellation
10-16 Domestic problem 10-67 Clear for net message
10-17 Meet complainant 10-68 Dispatch information
10-18 Quickly 10-69 Message received
10-19 Return to 10-70 Fire alarm
10-20 Location 10-71 Advise nature of fire
10-21 Call by telephone 10-72 Report progress of fire
10-22 Disregard 10-73 Smoke report
10-23 Arrived at scene 10-74 Negative
10-24 Assignment complete 10-75 In contact with
10-25 Report in person 10-76 En route
10-26 Detaining subject, expedite 10-77 ETA
10-27 Drivers license information 10-78 Need assistance
10-28 Vehicle registration info 10-79 Notify coroner
10-29 Check for wanted 10-80 Chase in progress
10-30 Unnecessary use of use 10-81 Breathalyzer report
10-31 Crime in progress 10-82 Reserve lodging
10-32 Man with gun 10-83 Work school xing at ..
10-33 Emergency 10-84 If meeting … advise
10-34 Riot 10-85 Delayed due to …
10-35 Major crime alert 10-86 Officer/operator on duty
10-36 Correct time 10-87 Pickup/distribute checks
10-37 Investigate suspicious vehicle 10-88 Present telephone number of ..
10-38 Stopping suspicious vehicle 10-89 Bomb threat
10-39 Urgent, use lights and siren 10-90 Bank alarm at ..
10-40 Silent run, no lights/siren 10-91 Pick up prisoner/subject
10-41 Beginning tour of duty 10-92 Improperly parked vehicle
10-42 Ending tour of duty 10-93 Blockade
10-43 Information 10-94 Drag racing
10-44 Permission to leave for … 10-95 Prisoner/subject in custody
10-45 Animal carcass as … 10-96 Mental subject
10-46 Assist motorist 10-97 Check (test) signal
10-47 Emergency road repair 10-98 Prison/jail break
10-48 Traffic standard repair at … 10-99 Wanted/stolen indicated
Communications Math
There are numerous formulas and equations that pertain to the communications business. Many of these are very complex and probably beyond the primary (majority) of hobbiest. We will start this page with some of the basic math concepts. You might find some of these helpful, or just interesting. In any case, we will continue to add that which we think may be of further use to you. Your suggestions and recommendations are always welcome. You can e-mail them to us by clicking on the e-mail hyperlink found at the bottom of this document.
I know the frequency of my transmitter. What is the wavelength?
In meters: 300 divided by frequency in MHz
In feet: 984 divided by frequency in MHz
In inches: 11,811 divided by frequency in MHz.
I know the wavelength of my transmission. What is the frequency?
300 divided by wavelength in meters equals frequency in MHz. Example, What frequency has a 6 meter wave length? 300 divided by 6 equals 50 MHz.
I want to build a straight wire antenna. How do I calculate the length I need?
Full wave: 984 divided by frequency in MHz equals the length in feet
Three-quarter wave: 738 divided by frequency in MHz equals the length in feet
Five-eighths wave: 615 divided by frequency in MHz equals the length in feet
One-half wave: 492 divided by the frequency in MHz equals the length in feet
One-quarter wave: 246 divided by the frequency in MHz equals the length in feet
What is the formula for converting meters to feet?
Meters multiplied by 3.281 equals an equivalent length in feet.
What is the formula for converting feet to meters?
Feet multiplied by 0.3048 equals an equivalent length in meters.
What are some other common conversion formulas?
Inches multiplied by 25.4 equals an equivalent length in millimeters.
Inches multiplied by 2.54 equals an equivalent length in centimeters.
Inches multiplied by 0.0254 equals an equivalent length in meters.
Millimeters multiplied by 0.03937 an equivalent length in inches.
Meters multiplied by 39.37 equals an equivalent length in inches.
GENERAL RADIO FREQUENCY
SPECTRUM IDENTIFICATION
FROM TO DESCRIPTION
16Hz 16,000Hz Audio Frequencies
10kHz 30kHz Very Low Frequencies
30kHz 300kHz Low Frequencies
300kHz 3,000kHz Medium Frequencies
3MHz 30MHz High Frequencies
30MHz 300MHz Very High Frequencies
300MHz 3,000MHz Ultra High Frequencies
3,000MHz 30,000MHz Super High Frequencies
30,000MHz 30GHz Extra High Frequencies
