Question about Cobra 29 LTD CB Radio

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I have a cobra lxbt29 how long should coax be for dual antennaes

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  • Master
  • 438 Answers

1/4 wavelength approx 9 feet

Posted on Oct 15, 2013

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Posted on Jan 02, 2017

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Shuttle83
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SOURCE: CB transmission

Hello 64driver,

Make sure the radio is grounded properly and that the SWR is around 1.2:1, 1.3:1 is good but try to get it to 1.2:1. Also take a power output reading while keying the mic. To do this with your power meter put it in-line with the CB and your antenna and key the mic you should get about 4 to 5 watts PEP. If this is the case your unit is putting out the proper power level, if not have the power amplifier checked by a qualified repair shop.

I hope this helps

Shuttle83

Posted on May 14, 2008

  • 7 Answers

SOURCE: have cobra classic 29 nightwatch. have good

Try making sure the RF gain is up all the way. Make sure all connections are good and tight, use the best antenna you can get. I love the 102 inch steele whip myself, just depends on what vehicle it would be on. conditions here the last few months have been pretty good for 10 meter ham and other ham bands, pretty bad for cb because so much skip/

Posted on Jul 29, 2009

  • 773 Answers

SOURCE: 29 cobra ltd c.b. wont transmit or receive

make sure the RF gain is all the way up, and the dynamic is all the way up or most of the way up.

When you say the antenna is good, have you checked the SWR's and or have tuned the antenna to be the correct length for the radio? If this has not been done ever, your radio could be a brick.

Also, make sure the PA/CB switch is on CB. if its on PA(public address) it will not receive or transmit because it is on PA mode, which if you have one hooked up, a PA speaker, then you can talk to people through it out side your car.

Also, make sure the S/RF SWR CAL switch, its the first one on the left, is all the way up on S/RF. this is your signal/ receive setting for the meter. When you hold the key, does this needle swing forward? As well does the RX/TX light turn red? If it does, then the radio is transmitting.

There is another light on the radio under the TX/RX light. It is the Antenna warning light. If this light comes on when you transmit, or has come on all the time during transmit, and now it doesn't then the radio is a brick. That is a warning light. It means that the antenna is not matched, or has not been tuned to the radio. If this has not been done ever, you have killed the radio.

Here is why. When you transmit, you are sending off a radio wave. This radio wave, at 27mhz, is about 36 feet long. In order for the wave to radiate off the antenna, the length of the antenna has to match the length of the radio wave. Now it does not have to be a full 36 feet. It can be an exact multiple of 36 feet. In other words it can be 1/4( one quarter) or 5/8(five eights) of a wave in length. 1/4 of a wave is 108 inches, or 9 feet long. Your antenna is still probably does not seem 9 feet long, but there is usually a loading coil that is not exposed making up the rest of the length of antenna, so that it matches the length of the radio waves electrically. If you were to stretch the coil out with the antenna whip, it would be 9 feet long.

When the antenna does not match the wave length, part of the RF energy does not leave the antenna, and goes back down the feed line(coax) and hits the transmit transistor. Prolonged reflection to the transmit transistor, otherwise known as the final will blow it out. As well depending on how bad the length was off, the more off, the more reflect energy, the more RF energy you are blasting back into the radio, and this causes more things then just the transmit to blow out. Some time the receive goes along with it when it finally goes.

So if the RF gain is up all the way, which by the way is basically how much receive you have, and there really is no reason to have it down at all, and the CB/PA switch is on CB and the needle does not swing forward when its on the S/RF setting, chances are that the radio is now no good.

It is fixable, but if there are no CB shops near you then you will have to send it out. And Cobra will not cover this under warranty because its stated in their warranty that they do not cover damage due to high SWR.

Posted on Apr 06, 2010

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2 Answers

Bought a new cobra Every time mike is keyed it reads antenna warning Radio will transmit short distance and will on receive short distance Very short Cobra 29 L X B T LCD CB radio


The antenna warning is the key, the swr on the antenna/feedline is very high. check antenna connections, coax and connectors for damage

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If you have a SWR meter.put meter in line with coax. Dubble check coax and make sure its not pinched,cut. Antenna mount is tight and clean. No electrolysis build up At connection. Warning light is coming on for a reason. something is wrong in between radio and connection at the antenna.

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I bought a 1000 watt rating antenna with center coil for my cobra 75 wx st cb,is this a good antenna


    • The antenna is as good as your coax is. Make sure to get a nicely shielded coax.I like RG 213U coax for a setup. 1000 watts means that's what the max rated power handling capacity is. The general rule is go about half of that rating wise is the most you want to put into it.

Jun 21, 2012 | Cobra 75-WXST CB Radio

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I have a cobra 29 ltd the red antenna light was coming on replaced the coax with 18' coax have Wilson 2000 antenna calibrated radio red light still coming on and and swrs not staying consistent when...


Best way to locate the problem is connect the radio to a Dummy load known to be good====if swr still comes on it is in the radio--if not in the antenna system.

Apr 28, 2012 | Cobra Radio Communications

1 Answer

My swr are high with proper calibration


You may need to retune the antenna system if the coax has not been kinked or damaged. If you simply moved it over from the old rig, the antenna was tuned to that layout and the groundplane was the shell of the truck and chassis. The Cobra can tune it somewhat, but the best results are achieved with a baseline adjustment of the antenna. But check the coax for damage first, then check the connections to the antennas. If you are using a baseloaded whip, there is actually an inductor wound that attaches to chassis/coax ground, and it may be corroded. As may the center conductor terminal at the antenna.

If those sheck out okay Check to see if your SWR is higher on 40 than on 1, or if it is higher on 1 than on 40.

if it is higher on 40 than on one, shorten the antenna slightly, first and see how it looks.

If it is higher on 1 than on 40 try lengthen it slightly and see how it looks.

If you are running with dual whips, that complicates matters a little bit due to phasing.

I had set up a radio to be portable from vehicle to vehicle and found changing tuning length was always required when I moved it to a new vehicle. What made matters worse was I chose a cheap Walmart baseload and it had lousy quality coax.

Feb 20, 2012 | Cobra 29 LTD CB Radio

1 Answer

I have Cobra 29 LTD Classic and need to know how to take the old co-ax out to put a new one in????


you just unscrew the coax from the back of the radio. there is no coax in the radio. Coax is the wire that runs from the radio to the antenna.

Nov 14, 2010 | Cobra Radio Communications

1 Answer

I have a Cobra CB RAdio What model I don not know? It's similar to the cobra 29 Ltd. It has at least 6 knobs/dials. Anyway...I can broadcast out very clearly. However, when I go around a corner or...


id check the coax conector first then the wire and antenna if its not the conector or the coax try a differnt antenna if you still have problems its internal with the radio

Apr 04, 2010 | Cobra Radio Communications

1 Answer

Just bought a workman 3000 to 7500 watt cb antenna, ever heard of it?? Im going to hook it up at work monday, got a cobra 29 ltd + or - 30 watt output. 9' coax. the antenna has 8" of swr adjustment... for...


cobra 29 has a 12 watt final, doubt you will be doing 30 watts. 25 if your lucky. Use 18 feet of coax, you will get better broad band.

If the antenna comes with the whip in it already, its been tuned at the factory and you shouldn't change it yet.

If not, half way is okay. It still needs to be tuned on a meter. either the one in the radio or an inline.

Mar 06, 2010 | Cobra 29 LTD 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.

Apr 21, 2009 | Cobra 29 LTD CB Radio

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