Question about Cobra 29 LTD CB Radio

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Antenna We are using our cobras as a way to talk between different employees inside a building and was told that placing a magnetic antenna on the tin roof of the building will give enough ground. However the red light lights up on the radio saying it is out of tune. Do I need to go to a base station antenna when the people that are using it are only 100 ft apart.

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Re: antenna

Checking and setting the swr can only be accomplished with an inline swr meter, not with the radios swr cal switch and the radios meter. Once you have set the swr of the antenna, you cal the radios meter to reflect the actual swr reading and use it like a dummy light on a car, just as an indicator of high swrs. To set your swr:

You must have an inline swr meter, which can be purchased online or from a truck stop. The ones at truck stops are cheap ones, but will do the trick for the most part.

You connect your antenna 18ft coax to the antenna plug of the swr meter, and a jumper coax (any length) to the transmitter plug of the swr meter and then to the radio.

Close all doors and make sure no one is messing around with the vehicle or antenna. You must be set up as you would normally be transmitting.

Now set your cb radio to channel 40 and your swr meter to fwd. Key up your microphone1.gif and at the same time turn the set knob on the swr meter until the needle is at the line that reads set. Unkey your mic and set the the swr meter to ref. Key up again and note what your reading is. Now leave the swr meter in ref and turn the cb to channel 1. Key up and take your reading. If the reading on ch 1 is higher than ch 40 you must raise the stinger on your antenna. If ch 1 is lower than 40, you lower your stinger. You are trying to get lower than a reading of 3 and as close to 1.5 as possible. If you lower your stinger as far into the antenna as it will go and you need it shorter, you cut the bottom of your stinger no more than 1/2" at a time, and recheck your swr reading after each cut.

Once you have gotten the best reading you can, connect your antenna directly back to the radio.

The setting of your swrs is to make your antenna as efficient as possible, by trying to get it as close as you can to a 50ohm impedance. THE ONLY PART OF YOUR SYSTEM THAT CAN CHANGE YOUR SWR IS YOUR ANTENNA, not your coax and not your radio. Your radio and coax can give you false readings, but only the antenna can actually change the swr.

On the swr meter, the fwd/ref switch stands for forward (power that is being transmitted out) and reflected (power that is reflected back into the radio.

Just for information sake, the swr cal switch on your radio is used to set the meter to reflect the swr that your antenna is set at. The meter on your radio is like a dummy light on your car. ONCE AGAIN, YOU CAN NOT SET YOUR SWR ON YOUR RADIO, only the antenna.

Rollin CBs
Mt. Vernon, TX

Posted on Jan 23, 2008

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Re: antenna

Hi, Other than the ground, another reason the red (SWR) warning indicator lites up is mis-tuned antenna. Ground - for CB to work efficiently, the ground plane must be at least 9 feet; Antenna - the antenna must be tuned to the operating frequency (Channel) of your CB; Both interacts with each other and can cause the red warning light. Any antenna (even a mobile magnetically mounted) will do as long as it is rated for 27MHz, the big issue is how to get a ground plane of 9ft. If you plan to install it on a metal roof, that should be more than good enough to provide the necessary ground plane but your problem would be the coaxial cable going in to your radio (I expect it will be long). If I may make a suggestion, get hold of a mobile antenna with a magnetic mount. Put it on top of a metal filing cabinet, radiator grill or any metal furnishing of your office (as long as aesthetically acceptable to you). Get 2 pcs of an electrical wire (say #14) about 9; put 1 on each side of the base or bottom of the magnetic mount or the metal filing cabinet, the exposed portions may be covered by the carpet, plant boxes or whatever; doesn't really have to be that straight; you can do the same to the metal chassis of the CB radio; you can also put a grounding wire from the chassis of the CB radio to your metal plumbing. You can use the built-in SWR calibrating instrument of the radio to check if you have a low SWR. Ideally it should be 1.5 or lower. Hope this be of some help to your and give you ideas. Good luck and kind regards.

Posted on Aug 24, 2007

Re: antenna

Why dont you try some sort of walkie talkie? cb type or even the frs type should work just as well and require no outside antenna.

Posted on Feb 22, 2008

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a Cb(Citizens Band) radio usually only broadcast on frequencies 26.965 to 27.405 megahertz. It is for mostly short range use 3 to 20 miles range. It comes with legal power of 4 watts. Ranges average about 5 miles. Don't expect big results off this little low-power Am transmitter. A basic 40 channel radio, Microphone, and "Magnet Mount" antenna plus 12 volt Dc 5A power supply will suffice. Place the Magnet mount on a metal file cabinet inside your house. hook up the Radio Shack 12 volt 3-5 Amp power supply to your 40 channel radio, Say Uniden pro510xl or Cobra 19 plus mini compact about $39 for these types. A $20 Radio Shack magnet mount. Turn on radio an talk. If you live in the city near lots of friends who have one too. You can talk on a private channel like Ch#40 and talk all night. The waves get quieter at night and extend farther into the Ionesphere;conditions are favorable 8pm to 12am. You should talk loudly within 5-7 miles easy. I like friends nearby; who live within 3 miles of me. Don't expect Long Distance with these radios. Unless you buy a big 1000 Watt Rf Linear an Tower 100 ft. with big Antennas costing $10,000. But remember the FCC will knock on your door and may give you 5 years $10,000 fines for anything of Linear amps 1000Watts. Just stick with basic tune and adjust,power mics(Cobra sells best). Talk with friends about fishing,hunting,gardens,tools,cars,women etc. Have Fun!!!

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This link will take you to an article that will explain how to tune your antenna.

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