Question about Cobra MRF55 2-Way Radio

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Antenna mounting I have a 21 ft cuddy cabin and would like to install an MRF45 2 way radio. How can I install the antenna and be in compliance with FCC exposure recommendations?

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According to FCC rules RULE 8 - Antenna Height
{A} "Antenna" means the radiating system (for transmitting, receiving or both) and the structure holding it up (tower, pole or mast). It also means everything else attached to the radiating system and the structure.
{B} If your antenna is mounted on a hand-held portable unit, none of the following limitations apply;
{C} If your antenna is installed at a fixed location (whether receiving, transmitting or both) it must comply with EITHER one of the following:
[1] The highest point must not be more than 20 feet (6.10 meters) higher than the highest point of the building or tree on which it is mounted;
or
[2] The highest point must not be more than 60 feet (18.3 meters) above the ground.
{D} If your CB station is located near an airport, and if your antenna structure is more than 20 feet (6.10 meters) high, you may have to obey additional restrictions. The highest point of your antenna must not exceed 39.37 inches (1 meter) above the airport elevation for every 109.36 yards (100 meters, 1 hectometer) of distance from the nearest point of the nearest airport runway. Differences in ground elevation between your antenna and the airport runway may complicate this formula. If your CB station is near an airport, you may contact the nearest FCC field office for a worksheet to help you figure the maximum allowable height for your antenna.

Posted on Jul 20, 2009

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1 Answer

What antenna


If you cannot use a magnet mount antenna on the roof then a fiberglass antenna (top loaded) about 4 ft. tall mounted behind the cab on the bed rail.You can usually run the coax thru a rain drain hole in one corner of the bed. The antenna should be tall enough to where the top third of the antenna is above the roof. The taller the ant.is the better the SWR will tune.

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Looking for a 21" antenna for a Motorola SP10


There are custom made antennas for portables. But the better solution is by eradiostore, use a mag mount.1) custom portable antenna, expensive.2) Motorola adaptor to BNC to longer antenna (portable, car type or base station).
3) NO power increase, not only are those frequencies designed for low power the board inside the radio cannot handle the heat and is not changeable or adjustable.

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3 Answers

How do i install a cb radio on a pick up truck


You will need a CB radio antenna, The CB radio and mounting hardware as well as the power wire.

Choose a place to mount the radio. Mount it. Run the power wires from the radio to the fuse box. Put red wire in with the fuse that is hooked to switched 12 volt. Ground the black wire to any metal of the vehicle.

Next find a place to mount the antenna. If you use a mag mount, the roof of the cab is a best bet. Run the wire into the vehicle, it can go through the door, just make sure its not going to get pinched.

Hook the coax from the antenna to the radio

Now you have to tune the antenna. this is important because if you don't you you will blow the transmit final transistor out in the radio.

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

Nov 04, 2009 | Cobra 25 LTD 40-Channels Base CB Radio

1 Answer

I set the swr on my antenna and it keeps moving i have a cobra 19 dx iv and i just installed a net window mount antenna 27" on my back window that has factory tint.


1) if you are talking, your SWR will most likely move. You must take the reading while not modulating, (talking into the mic)

2) Window mount antenna's are GARBAGE. they are worthless. BAD BAD BAD. You wasted your money. Get a mag mount.

3) if you are not in an open lot, your SWR's will be different due to structures reflecting signal back. Always take your SWR reading in an open lot.

4) You could be experiencing Common mode currents. Normally the signal travels on the inside of the coax ground. Common mode current is when the signal is traveling back down the coax on the outside of the ground in the coax. (The biggest cause of this would be the window mount antenna). If you want to keep that garbage antenna, then you can make an RF choke in the coax. The best solution is get a better antenna. Here is how to make the choke. As close to the antenna as you can, take 6 ft of coax and loop it uniformly laying each coil next to the other. use electrical tape to hold it in place. You want 6-8 wraps. You want a nice uniform coil.


Just get a better antenna. Window mounts are the worst. You get horrible receive and horrible transmit. Get a wilson 500 mag mount. It will work so much better for you.

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you need a swr meter to check your standing wave.

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1 Answer

No radio


Your radio is most likely shot because if your antenna is not hooked up you will still have radio channels and time displace come up on your radio. If your antenna is broke then you will have to repair it to.

Feb 04, 2009 | 1991 Chevrolet S-10 Blazer

1 Answer

Non grnd steel antena


I assume your coax is not hooked up properly or you have some kink of a short in your antenna connection ( thats if your cb is working properly ) Radio Shacks Information that suggested that the 102" whip is the perfect antenna is their opion only as I prefer to recommend a full wave antenna system to my customers, but I do assure you, the 102" whip does work well if it's properly installed. I have found the main problem in the 102" whip installation is when the center hole is cut to install the antenna, it's not cut big enough, which grounds the antenna. It's not suppose to be grounded in any fashion to the automible chassis. The ground of this antenna comes from the 3 screws mounted around the outside of the antenna mount. Check that for sure. If you can't correct the problem. write me back at this web sight of direct at wyoed1@aol.com. Good Luck
Ed
NC Electronic
Mills, Wyoming

Dec 19, 2007 | Uniden Bearcat Pro PC68XL 40-Channels Base...

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