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What is the effective range of my Cobra CB radio?,
Unfortunately, there is no easy answer to this question.
All Cobra CB radios transmit using the maximum FCC allowable power output which is four watts of power. The amount of power that actually gets out can be affected by the type of antenna used, it's condition and location, the physical length of the whip and more importantly the proper matching of the standing wave ratio or SWR. For more information on setting the SWR access the FAQ on All About SWR.
Other factors that can enhance or detract from the effective range is the environment that the CB is used in. Tall buildings, trees, hills, and interference from other CB radios all limit the effective range of a CB radio. Certain atmospheric conditions can also limit the range of your Cobra CB radio.
If we were able to eliminate all negative environmental factors, a properly set up base station could transmit 10 to 15 miles, a mobile unit 5 to 7 miles and a hand held unit approximately 2 miles with the only variable being the type of antenna used with your unit. Unfortunately, these optimum conditions don't exist and the range of your unit will be less depending on the conditions you are operating in.
Are FRS and GMRS radios compatible with CB?,
FRS and GMRS are relatively new radio bands which have been opened to the general public.
FRS and GMRS radios are compact handhelds and use FM transmission in the UHF radio band.
They are very handy for personal communications such as at malls, carnivals, vacations, etc.
Any time you need to keep in touch.
Range will vary between 1 to 5 miles depending on terrain and the particular model you choose.
Cobra offers a variety of models.
FRS and GMRS radios operate at a much higher frequency than CB (approximately 465 megahertz, compared with 27 megahertz for CB).
They therefore cannot communicate with a CB radio.
What is the range of my handheld CB radio?,
The range of a handheld CB radio is dependant on a number of factors.
This document describes what to expect, and how to maximize range.
When using the stock "rubber duckie" antenna, typical range is approximately 1 mile under optimum conditions (flat, open terrain).
Actual range will vary depending on conditions.
The short "rubber duckie" antenna is very convenient, but is not ideal for long range communications.
For increased range, use a telescoping antenna such as the Cobra HA-TA.
The following conditions will reduce the operating range:
The batteries are wearing-out.
There are hills, trees, or buildings between radios.
One or both radios are inside a house.
Using the rubber duckie antenna inside a car will result in very short range.
For use in a car, a mobile antenna (such as a magnet mount) is highly recommended.
An adapter such as Cobra part number HA-BNC will be required to connect the radio to a mobile antenna.
A suitable adapter is also available from Radio Shack.
For optimum range, try the following:
Make sure the batteries are in good condition.
If the radio has a high/low power switch, use high power.
Turn on Soundtracker (if equipped).
Turn the squelch control all the way down.
Select a quiet channel (one with low background noise).
Speak about 1-2 inches from the microphone slot.
This will increase modulation and make you sound louder.
What are the CB Frequencies?,
CB Frequencies (in megahertz)
CB Channel
Frequency
CB Channel
Frequency
01
26.965
21
27.215
02
26.975
22
27.225
03
26.985
23
27.255
04
27.005
24
27.235
05
27.015
25
27.245
06
27.025
26
27.265
07
27.035
27
27.275
08
27.055
28
27.285
09
27.065
29
27.295
10
27.075
30
27.305
11
27.085
31
27.315
12
27.105
32
27.325
13
27.115
33
27.335
14
27.125
34
27.345
15
27.135
35
27.355
16
27.155
36
27.365
17
27.165
37
27.375
18
27.175
38
27.385
19
27.185
39
27.395
20
27.205
40
27.405
How to choose a CB antenna.,
Choosing a CB antenna can be a bit tricky, but only because there are so many choices.
This document describes the various styles of CB antennas.
The first step in choosing an antenna depends on the type of vehicle you have.
If you are mounting an antenna to a boat or fiberglass RV, you need a special type of antenna called a "no-ground-plane" antenna.
Most CB antennas require a large metal surface (called a "ground plane") in order to work properly.
Boats and fiberglass vehicles lack a proper ground plane.
A no-ground-plane antenna is specially designed for these applications.
You can find these antennas at Radio Shack and places that sell boating and RV accessories.
Please note that it is important not to modify or change the cable that comes with the antenna.
The cable is specially matched to the antenna.
There are not many choices of no-ground-plane antennas, so you will have to work with the styles you find available.
They are typically fiberglass antennas, and mount using some kind of clamp-type bracket (except for the glass-mount type).
If you need a no-ground-plane antenna, then you are done with this document (but you can skip below to the glass mount antenna).
Otherwise, keep reading.
The next step in choosing an antenna is choosing a mounting method.
Listed below are some popular styles:
BASE STATION
If you are using a CB radio in your home, you will need a base-station antenna mounted on your roof.
You do NOT want to use a mobile antenna.
Mobile antennas are designed strictly for vehicles and will not work properly for base-station use.
And any kind of indoor antenna will get truly lousy range.
Base-station antennas are installed using the same type of hardware as TV antennas.
Since the cable run can be rather long, it is best to use RG8 cable which has low loss.
Base station antennas are available from a variety of vendors.
Try browsing on the internet.
MAGNET MOUNT
A magnet mount antenna means just what it says.
A large magnet keeps the antenna on the car.
The magnet has a plastic covering so that it does not scratch the paint.
The antenna can be mounted on the roof or the trunk lid, but roof mounting provides better performance.
The cable is brought inside the car, and the door or trunk lid is closed over the cable.
Or the cable can be brought in through the window.
Magnet mount antennas are quick to install, easy to remove, and are easily transferred from one vehicle to another.
TRUNK LIP MOUNT
The trunk lip mount clamps on the edge of the trunk lid.
It is usually mounted along the front of the trunk lid, just behind the rear window.
It can also be mounted along the side edge of the trunk lid.
No drilling is required.
BUMPER MOUNT
This is the place to choose if you want to use one of the really long whips.
You can also mount a fiberglass antenna to the bumper.
It will be necessary to drill a hole for the mount.
If you use a fiberglass antenna, choose one that extends at least a foot above the roof of the vehicle.
Bumper mounts are more difficult to install on vehicles with plastic bumpers.
MIRROR MOUNT
Popular on trucks, the mirror mount antenna clamps onto the mirror bracket.
Plastic mirrors won't work, the mirror must have a metal bracket.
In addition, it is important that the antenna clamp gets grounded to the vehicle.
If the door is fiberglass, it will be necessary to run a ground wire to the antenna clamp.
Use 14 gauge wire, connected to the nearest ground point on the chassis (such as the door hinge).
GUTTER MOUNT
A gutter mount antenna clamps onto the rain gutter above the door.
Actually, most modern cars have done away with rain gutters to improve aerodynamics.
After mounting, the antenna cable is brought inside the vehicle and the door is closed on the antenna.
Or the cable can be brought in through the window.
GLASS MOUNT
A glass mount antenna mounts to a window on the vehicle.
It is a permanent mount, and should not be mounted to any glass that rolls down or swings open.
This type of antenna is short, and looks similar to a cell phone antenna.
The antenna is mounted on the outside with double sided tape, and a small box is mounted in the exact same spot inside the vehicle with double sided tape.
The antenna should not be mounted over any metallic tint or over defroster lines.
Because of the short antenna and some signal loss through the glass, this type of antenna is one of the poorest performers.
But it does offer a solution if other mounting methods are not acceptable.
The glass mount antenna is a no-ground-plane antenna, and is therefore suitable for fiberglass vehicles and boats.
DUAL ANTANNAS
Dual antennas (also called co-phased antennas) are popular, more for looks than for performance.
They are typically mounted using mirror mounts.
This type of configuration provides increased range to the front and rear, and reduced range to the sides.
For proper co-phasing, the antennas should be mounted approximately 9 feet apart.
This limits the application to large trucks; your typical pickup is too narrow to provide 9 foot spacing.
Co-phased antennas require 75 ohm cable (rather than the 50 ohm cable used for single antennas).
Actually for overall use, a single antenna works just as well.
COMBINATION ANTENNAS
These are hard to find, but there are AM/FM/CB combination antennas.
There is also a splitter device available which allows using the AM/FM antenna as a CB antenna, thus achieving the same result.
There is no unsightly CB antenna, just the regular AM/FM antenna.
But this is one of the worst performers for CB use.
Using the AM/FM antenna compromises CB performance.
Your final decision on an antenna may be influenced by the following:
LENGTH
This is THE MOST important characteristic that affects performance.
The longer the antenna, the better the range.
A cheap 60 inch antenna will outperform an expensive "top-of-the-line" 30 inch antenna.
Go with the longest antenna that is practical.
The best performer is a 1/4 wave antenna, which is 108 inches long.
That may be too long for you, but just remember that longer length equals better performance.
Incidentally, you may see 102 inch whips.
The missing 6 inches is made up by the mount.
STEEL OR FIBERGLASS
The only theoretical advantage of a fiberglass antenna over a steel whip is that the fiberglass antenna will stay more vertical at highway speeds.
But actually there is not any noticeable difference in performance.
Go with the style that you like best.
LOAD
Unless you are going with a 1/4 wave whip (108 inches), your antenna will have a "load".
The load is a special wire coil which makes the antenna look like it is 108 inches long (electrically).
The radio cannot tell the difference.
The load is located either at the base, the center, or the top.
Because of the weight, only the stiff fiberglass antennas can be top loaded.
As far as performance, the location of the load is not critical.
But here is an example of when it might be important:
lets say you have a bumper mount antenna on a minivan, and the antenna extends one foot above the roof.
In this case much of the antenna is right next to the body of the vehicle, which will tend to reduce performance.
Getting the load above the vehicle will help.
So the best choice would be a top loaded antenna.
WEATHER RECEPTION
Some CB radios provide reception of government weather broadcasts, which is a nice feature.
But not all CB antennas are compatible with weather reception.
Here are the rules:
All center loaded and top loaded antennas are compatible with weather reception.
Not all base loaded antennas are compatible with weather reception.
If you are buying a base loaded antenna, make sure it says that it is compatible with weather reception.
OK!
Now you have finally chosen an antenna and installed it and are happy.
The last thing you need to do is adjust (tune) the antenna for proper operation in the CB band.
This is accomplished by checking the "SWR" of the antenna.
Most CB antennas are adjustable, which should be described in the instructions that came with the antenna.
(You DID save the instructions, didn't you??)
A separate document is available which discusses SWR.
What is Single Sideband?,
All CB radios operate on AM, which is the same type of transmission as your typical AM radio station.
In addition, some high-end CBs (such as the Cobra 148) are equipped with single sideband.
Single sideband is a different mode of transmission.
People using a regular CB radio cannot properly receive single sideband, it will sound garbled.
Here is a brief description of single sideband:
All AM transmissions take up a certain amount of space, called "bandwidth".
The bandwidth for CB radios is 8KHz (kilohertz).
As an example, lets look at channel 19.
The frequency of channel 19 is listed as 27.185MHz (megahertz), but the signal actually consists of a range of frequencies.
The range is 4KHz below and 4KHz above (making an 8KHz bandwidth).
So the actual range of channel 19 is 27.181 to 27.189MHz, with a center frequency of 27.185MHz.
The range of frequencies below 27.185MHz is called the Lower Sideband (LSB).
The range of frequencies above 27.185MHz is called the Upper Sideband (USB).
So AM transmissions consist of a lower sideband and an upper sideband.
CB radios equipped with single sideband can operate on just one of the sidebands (lower or upper).
So in effect you have extra channels.
A person operating on channel 19 LSB will not interfere with a person operating on channel 19 USB.
In this manner an SSB radio offers 80 discrete channels.
You don't really get 120 discrete channels (40 AM plus 80 SSB) because there will be interference between AM and SSB.
If someone is operating on channel 19 AM, it will interfere with sideband transmissions and vice versa.
But you do get 80 discrete SSB channels in addition to the regular 40 AM channels.
Radios equipped with single sideband have an additional control, usually called a "voicelock" or "clarifier".
This control is adjusted to clarify received signals when using single sideband.
This is necessary because there is not enough information in an SSB transmission for the receiver to properly decode the signal.
A manual control is necessary to clarify the reception.
This typically needs to be done only once when communicating to a person on SSB.
The advantages of single sideband:
More channels
Higher power (12 watts is allowed on SSB, only 4 watts is allowed on AM)
Quieter reception
One interesting difference between AM and SSB is that single sideband only transmits a signal when you talk.
If you key the microphone on AM, the power meter will always indicate transmit power.
If you key the microphone on SSB, the power meter will not indicate power unless you talk.
In addition, the power meter will fluctuate with your speech.
This is normal operation for SSB.
One other note: As previously stated, a person on AM will not be able to understand an SSB transmission.
However, it is possible to receive AM transmissions when you are on sideband.
If a person transmits on channel 19 AM, it will be possible to properly receive him on either USB or LSB.
This is normal.
So if you are trying to talk to someone on SSB and they don't respond, switch to AM and see if they are operating on AM.
All About SWR,
What is SWR?
SWR is short for "standing wave ratio".
It is a measure of how well the antenna is performing.
Most problems with the antenna or antenna cable will show up during an SWR check.
Please note that the SWR is a measure of antenna performance.
A poor SWR is caused by the antenna, the antenna cable, or a poor antenna installation.
Poor SWR is not caused by the radio.
Since the SWR is a function of the antenna system, changing radios will not affect the SWR.
Why is SWR important?
SWR readings typically have a range of about 1 to 10.
The lower the number, the better the antenna is working.
As the SWR climbs, both transmit and receive range will drop.
An SWR of 1 is perfect, but it is not possible to get a perfect reading on all 40 channels.
When an antenna is properly adjusted, the SWR is will be highest on channels 1 and 40, and lowest on channel 19.
This gives the best performance throughout all 40 channels.
The SWR must never exceed 3, otherwise the transmitter in the CB radio can overheat and eventually fail.
Excessively high SWR can also cause other problems such as a squealing noise, or can cause interference with other electronic devices in the vehicle.
An SWR of 2 or less is very good, and an SWR of 1.5 or less is excellent.
How can I measure my SWR?
SWR is measured using an SWR meter.
Some higher-end CB radios have a built-in
SWR meter, which is very convenient (such as Cobra models 29 and 148).
Other models must use an external SWR meter and a short "patch cable".
An external SWR meter will have 2 connectors on the back.
The antenna cable will screw onto the connector marked "ANT".
The patch cable will screw onto the other connector.
The other end of the patch cable screws onto the CB.
The patch cable needs a PL-259 connector on each end.
The patch cable should be kept as short as possible, no longer than 3 feet in length.
Where can I get an SWR meter?
SWR meters can be found at places that sell CBs and CB accessories.
This includes CB shops, truck stops, and Radio Shack.
What is the procedure to check SWR?
The procedure for checking SWR is basically the same whether using a built-in meter or an external meter.
Follow the instructions that come with the meter.
Here is the basic procedure:
SWR must be checked in an open area.
Park the vehicle away from buildings and trees, which can affect your readings.
Do NOT check SWR inside a garage!
Close the doors, hood, and trunk lid.
Select the channel to check.
It is recommended to check channels 1, 19, and 40.
Set the switch to the CAL, FWD, or FORWARD position (depending on the meter).
Push the transmit button on the microphone, then adjust the calibrate knob so that the needle goes to the cal marker on the display.
The cal marker is always located on the far right-hand side of the display (maximum deflection).
It will say either CAL or SET.
While still holding the transmit button, set the switch to the SWR, REF,
or REFLECTED position (depending on the meter).
Read the SWR on the meter.
On Cobra CBs, the top scale of the meter is the SWR scale.
When you switch to a different channel, you should always re-check the CAL setting (repeat steps 4 through 7).
How is the SWR adjusted?
The object is to get the SWR the same on channels 1 and 40, and below 3.
Whatever you do, make sure the SWR is below 3.
Once the SWR is the same on channels 1 and 40 and is also less than 3, the antenna is tuned for optimum performance.
Begin by checking the SWR on channels 1 and 40, then refer to the following:
If the SWR is higher on channel 1, the antenna is too short.
If the SWR is higher on channel 40, the antenna is too long.
An adjustment is made to the antenna (refer to the antenna instructions), then the SWR on channels 1 and 40 is re-checked.
This process is repeated until the readings are about the same.
Remember that the readings must also be below 3.
When you are done, check the SWR on channel 19.
It should be even less than what you got on channels 1 and 40.
Most antennas are adjustable.
Refer to the instructions that came with your antenna or call the manufacturer.
If you have dual antennas, make equal adjustments to both antennas.
Here are a few methods, which vary with manufacturer:
Antennas with a steel whip are usually adjusted by loosening a set screw and raising or lowering the whip.
If you have a center-loaded antenna (fat section in the middle of the whip), adjust the top whip up and down.
Even if the instructions do not refer to raising and lowering the whip, virtually all whip antennas can be adjusted in this manner.
Some models have a metal collar which is turned, or a sleeve that slides up and down.
Fiberglass antennas can be adjusted as follows:
Remove the plastic cap from the tip of the antenna.
Slit the plastic cover to expose the top coils of wire.
To shorten the antenna, cut off the top coil.
To lengthen the antenna, pull up the top coil.
Replace the plastic cap and check the SWR.
It is best if you refer to the specific instructions for your antenna or call the antenna manufacturer.
For instance, some fiberglass antennas have a sleeve which you slide up and down to adjust the antenna.
I can't get my SWR down
If you can't get your SWR below 3:
A.
There may be a problem with the antenna installation.
Refer to the installation instructions that came with the antenna, and check your installation.
Mirror-mount and trunk-lip-mount antennas typically must have good electrical contact with the frame of the vehicle.
If a mirror bracket is mounted to a fiberglass door, try running a short, 12 gauge ground wire from the antenna bracket to the door hinge.
On a trunk-lip-mount, you may need to scrape the paint away where the set screws contact the trunk lid.
Or, you may need to run a ground strap from the trunk lid to the frame.
Mounting the antenna to an aluminum surface (tool box, etc.) may not provide a good ground, which can cause high SWR.
This is because aluminum is not a good
conductor.
A grounding problem can also occur if mounting to a luggage rack.
You can try running a ground wire to the antenna mount, but you may need to relocate the antenna.
It is also possible that you are not using the right kind of antenna.
Most CB antennas must be mounted to a metal surface ("ground plane") in order to operate properly.
The metal body of the vehicle serves this purpose.
On fiberglass or plastic body vehicles, a "no-ground-plane" antenna is needed.
This type of antenna is specially designed to operate without a metal surface.
B.
The antenna cable has been shortened or lengthened.
Changing the length of the antenna cable can affect the SWR.
If your antenna came with cable, DO NOT shorten the cable.
If your antenna did not come with cable, try using an 18-foot cable.
If you have extra cable, do NOT tightly coil the extra length.
You can run it back-and-forth inside the vehicle, or coil it in at least a 12 inch diameter loop and then tape the middle together into a bow shape.
If you need to lengthen the cable, use an in-line coupler and add lengths in multiples of 3 feet.
You can also contact the antenna manufacturer for recommended lengths.
C.
The antenna cable is damaged or the antenna mount is shorted.
This usually results in an extremely high SWR.
If the needle is going all the way to the cal marker (or beyond) when you try to read the SWR, then either the cable is damaged or there is a problem with the antenna mount.
Use an ohm meter to test as follows:
Disconnect the antenna cable from the radio and use the ohm meter to measure between the center conductor and the connector shell.
Use the highest range on the ohm meter.
If you get a reading, then there is a problem with either the cable or the antenna mount.
Disconnect the cable from the antenna and repeat the test.
If you still get a reading, the cable is bad.
If you no longer get a reading, then there is a problem with the antenna mount.
D.
The whip may be too long (steel whip antennas).
If you have pushed the steel whip all the way down and the SWR is still higher on channel 40, then the whip is too long.
In this case, it is permissible to shorten the whip by cutting the end.
If the whip is painted, scrape the paint away after cutting so that there is good electrical contact with the set screw.
DO NOT cut more than 1/4 inch at a time.
Before cutting, refer to the above (A through C).
Your trouble might be an installation problem, not that the whip is too long.
Be careful!
If you cut too much, you may wind up with an antenna that is now too short.
The only remedy for a short antenna is to get a new
whip.
E.
The whip is too short (steel whip antennas).
Again, first refer to the above (A through C).
Your problem may be installation-related.
But it is possible that certain applications may require a longer whip than what was supplied by the manufacturer.
If you have raised the whip as high as it can go and the SWR is still higher on channel 1, contact the antenna manufacturer.
What is CB?,
CB (Citizens Band) radio is simply a 2-way voice communication system that lets you talk to other CB users.
It lets you talk from your truck, car, home, business, or boat to any other CB operator on the same channel.
Technically, it is a transceiver.
It functions both as a radio transmitter (when sending messages) and a receiver (when receiving messages).
Citizens Band Radio was created by the Federal Communication Commission (FCC) in 1958.
In that year the FCC authorized 23 channels for private citizen use.
CB’s popularity soon congested these channels, so the FCC added 17 more channels for a total of 40, effective January 1, 1977.
Do I need a license to operate CB?
No.
The FCC used to issue licenses for CBs, but they discontinued that requirement many years ago.
Is a CB complicated?
No.
There are only three basic controls on a CB radio.
One is used to turn the set on and off and to control the volume of incoming signals.
The second control has a very appropriate name:
“Squelchâ€쳌.
When adjusted properly it keeps your radio silent until an actual message is received.
The third control is the channel selector, which allows you to change channels.
These are the basic controls of a CB radio.
More sophisticated radios have more controls, but if you can operate these three then you can operate any CB radio.
How far can I talk on a CB?
How far you can communicate depends on a number of things:
natural obstructions such as hills and valleys; radio interference and atmospheric conditions; man-made obstructions like bridges and tall buildings.
Normally, communications are limited between five and seven miles depending on the above conditions.
How to choose a CB radio.,
CB radios all have pretty much the same receive sensitivity.
In addition, CB radios are limited to 4 watts of transmit power per FCC regulations.
Therefore, all CB radios have pretty much the same transmit performance.
Spending more money will generally not get you better range, but certain features can help maximize range.
For example a Noise Blanker can help eliminate noise, which can improve reception of weak signals.
And an SWR meter can help maximize the performance of the antenna.
There are numerous features that are available by spending a little extra on a radio.
Here is a list of popular features:
Noise Blanker
A noise blanker is particularly effective against ignition noise and other types of "impulse" noise.
It provides improved filtering for clearer reception.
RF Gain Control
The RF Gain controls the sensitivity of the receiver.
Normally you would have it turned all the way up for maximum sensitivity (and maximum range).
But if you are receiving a fairly strong signal, the RF Gain can be turned down.
This will provide very quiet reception.
The RF Gain is particularly useful during noisy reception conditions.
SWR Meter
An SWR meter lets you check how well the antenna is tuned to the CB band.
Adjusting the antenna for a low SWR is one of the best ways to get maximum range.
Radios with a built-in SWR meter let you easily check the SWR at any time.
A separate ducument is availabe about SWR.
Dynamike Control
The Dynamike is a microphone amplifier.
It is like having a "power mike" built into the radio.
Amplifying the microphone output will help maximize your talk volume and make it easier for other people to receive your transmissions.
Weather Channels
The National Weather Service transmits local weather broadcasts throughout the USA.
Some CB models include a weather receiver built right into the radio. This makes it easy to receive local weather reports during your travels.
Single Sideband
Single Sideband is the one exception where more money definitely gets you better range.
Single sideband (SSB) is a different mode of transmission than regular CB (which uses regular AM transmission).
Not only does SSB provide quieter reception, but the FCC allows 12 watts of transmit power.
This will provide significantly better range.
A separate document describes single sideband in more detail.
Conclusion
Choosing a CB radio boils down to choosing a model with the features you want.
A basic model will provide excellent performance, while more advanced models will provide extra features to maximize your enjoyment.
