Question about Cobra 29 LTD CB Radio

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I have the cobra 29 classic k40 antenna. The antenna light comes on when keyed up on 40 but only channel 40. I used an swr meter and that's as good as I can get. Is this ok?

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Normally the swr should be set on the centre channel so if you have 40 channels you should set it on channel 20. This is because as you move away from channel 20 the swr rises slightly more for each channel away from the 20. If you set it on channel 40 you'll have twice as much swr on channel 1 more than if you set it on channel 20. If the swr metre shows 1:1 (i.e. doesn't move up at all) on channel 20 the rest should be ok since the antenna was designed for CB. You should however check that the needle showing reflected power doesn't go above 2.5

Posted on Jul 30, 2010

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Cobra 29 now Ltd classic Cobra 29 nw.ltd classic receives not well but does not transmit don't even move the swr./power meter any ideas


High SWR on antenna system.. may have mess up your RF final transistors. if you were talking on it for a long time. have someone check the SWR on the antenna system... should be a FREE service.

Jul 13, 2014 | Radio Communications

1 Answer

How do you set the SWR on a cobra 29 LTD classic radio


the same way you set it on any other radio.Look at the face of the set,you will see a switch that says S/RF,CAL , SWR. Now look at your meter and you will see a triangle that shows cal.Put your set on ch 1 with the switch in the cal position and bring the needle to that calibrate line on the meter by keying the mic. now release the key and set switch to SWR and key the mic again.Now write this reading down.Repeat for channels 40 and 19. If the reading is higher on 40 than on 1 you need to shorten the ANTENNA.If its higher on 1 than 40 you need to make your ANTENNA longer Always check 19 to make sure you have an average SWR. Any reading under 1.9:1 is good

Jun 15, 2014 | Cobra 29 LTD CB Radio

1 Answer

A k 40 magnetic antenna has high swr and wire and everything looks fine


The K40 is known to fail after that many years in service when moisture gets into the coil it causes it to change it resonance freq. and hence the higher SWR. Buy and new antenna and enjoy 10 years is way to long for an antenna to last.

Apr 05, 2014 | K40 CB Antenna K-30

1 Answer

I have a cobra 29 wx nw st withwilson little wil entenna. I am having issues with a no swr reading on channel one even if I turn my swr cal all the way up. My 40 cal reads on the swr at .5 no matter how...


first of all you are going about it wrong. To set your SWR you check it on channels 1 , 19 , and 40. If you reading is higher on 1 than on 40 you have to shorten your antenna . if its higher on 40 than on 1 then you have to lengthen it. before you do any adjustments to it ,loosen the set screws and let the antenna fall to the bottom then bring it up 1/4 " and tighten the screws. You should also use an external SWR meter not the one on the radio. Thats good for making checks every once and a while. With the meter you key the mic and have the needle go to set then put it on for and key the mic to obtain you reading . Anything under a two is good .

Dec 16, 2010 | Cobra 29 WX NW ST 40-Channels Base CB...

1 Answer

Every time I press my MIC to speak into it the red lights on the RX/T and ANT light come on alerting me of a problem. How can I fix this.


RX/TX light should change to red, however the ANT light is a bad light. This means that your antenna is not adjusted properly. Do not key the radio or talk on it for any other reason then to check the SWR and tune the antenna. If you have the manual that came with your cobra 29, there is a section that explains how to check the SWR. And the manual for the antenna, it will explain how to adjust it.

If not, here is how to do it.........

How to check the SWR on a Cobra 29

Step 1. Find out what your current SWR is on the center of the band.

  1. Turn the radio to channel 20.
  2. Set the S/RF SWR CAL switch to CAL.
  3. Turn the CAL knob all the way counter clockwise.
  4. Key the radio. Do not talk into the mic.
  5. While holding the mic key, turn the CAL knob to the right until the needle reaches the CAL mark on the top right of the meter.
  6. Now flip the S/RF SWR CAL switch to SWR while still holding the key on the mic.
The needle should fall. Where ever the needle is while holding the key is your SWR reading on channel 20. It should be as low as possible. If its a reading of 2, then its not gonna kill the radio but is border line. Any higher and its bad. Using the radio like this will damage the final output transistor. If its less then 2 this is better. You want it to be less then 1.5 or better.

The ANT light may come on with an SWR of 2. running the radio with an SWR of 2 shouldn't hurt the radio, but I don't like to mess around. Get it as low as possible.

How to adjust the antenna for SWR

The length of your antenna will change your SWR. SWR is basically how much RF energy is not leaving the antenna and getting reflected back into the radio. That's why it hurts the radio when its high. An antenna has to be the right length, matching the length of the radio waves in order for it to radiate all of the RF energy out of the antenna.

Most antennas have a way of lengthening or shortening the antenna. If its a mag mount antenna with a metal whip, there is probably a set screw that when loosened, will allow you to raise or lower the whip. If its a fiberglass antenna, under the rubber cap at the top is how you raise or lower the antenna.

Figuring out if your antenna is too long, or too short

Here is how to know weather or not you have to lengthen or shorten your antenna.

  1. Take an SWR reading as explained in the first step on channel 1. Write down the SWR for reference.
  2. Take another SWR reading on channel 40. Again write it down for reference.
Now if the SWR is higher on channel 1 then on channel 40, its too short. You need to make it longer.

If the SWR is higher on channel 40 then channel 1, then the antenna is too long. You need to shorten it.


Make small adjust ments about an 1/8th to a 1/4th inch at a time. each time checking the difference between channel 1 and 40.

You will know when you are a good match when there is little to no difference between channel 1 and 40's SWR. Once you are satisfied that the difference between 1 and 40 is about the same, and much lower, then turn the radio back to channel 20 and take an SWR reading.

You will now find that the SWR on channel 20 is really low. Most likely under 1.5 or better, Almost nothing on the meter.


Here is a Meter Key, so you know what you are looking at.
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Oct 11, 2010 | Cobra 29 LTD CB Radio

1 Answer

How to set SWR readings to my K40 Antenna without a meter


If you have a cobra 29 then you have a meter. There is no way to Tune an antenna without a meter. You need a device that can read the reflect, or Standing Wave Ratio.That is a standing wave of RF energy that instead of leaving the antenna, is going back down the feed line to the radio and in time hurting the radio.

If you have a cobra 29 LTD, it has a build in SWR meter. It is not as accurate as an in line meter, but it will get it close enough not to hurt the radio. Here is how to do it.

Turn on the radio, with the antenna hooked up. Never key with out an antenna hooked up.

Set the switch all the way to the left(S/RF SWR CAL) to CAL. this stands for calibrate.

You will notice there is a knob right next to the channel selector knob marked SWR CAL as well. Start with the knob turned all the way to the left.

Put the radio on Channel 20. This is just about the middle of the band.

Key the radio and hold it. While holding the key on the mic, turn the SWR CAL knob up until the needle on the meter hits the mark "CAL". there is a triangle, and a gap in the line. The needle needs to be at the point of the triangle in the gap.

NOW, while still holding the mic key, flip the switch from CAL to SWR. You should see the needle immediately swing back. What ever the needle is on at this point is your SWR reading. use the set of numbers on the top of the meter, that's for SWR measurement.

If the needle does not swing back, and is in the rad, the antenna is WAY off. There are some reference points on the scale. The first gap in the line is 1.5 SWR. if the needle is there or less that is fine. then you have 2 and 3. 2 is not so great, but not extremely bad, but you should try to get it lower. 3 is really bad. Anything past 3 is considered infinity, and is really really bad.

If its high, then your antenna is either too long or too short. So how do you know which?

Here is how.

Turn to channel one and repeat the SWR process from above. Make note of the reading.

Then turn it to channel 40. Repeat the process again and take note of the reading.

Now, if the SWR is higher on channel 40 then 1, then your antenna is too long and you must shorten it. If the reading is higher on 1 then 40, then your antenna is too short, and you must lengthen it.

Make adjustments in length about an 1/8th inch at a time until you have either the same reading on 1 and 40 or real close, and or the reading on channel 20 is really low.

If you get it so that the reading on 1 and 40 are the same, then the SWR reading on 20 will most likely be almost nothing, unless there is either something wrong with the antenna, coax, or its just a crappy antenna.

K40 should be able to get a nice low SWR.

Apr 04, 2010 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29 NW LTD Classic wont calibrate and red antenna light keeps coming on


The calibrate knob only calibrates the radios SWR meter, the owners manual will show you the procedure for that. If your ANT light is coming on, it is telling you that your SWR is to high, and may cause damage to the radio from reflected power. You should purchase an in line meter as the radios internal meter may be somewhat unreliable. You need to tune the antenna to the lowest SWR possible. Typically anything under 2.0:1 is acceptable. Radio Shack sells a meter for about $50, and is pretty accurate. Antenna mounting can also cause high reflection if it is to close to other objects. Google "CB antenna tuning" or read the instruction manual for you antenna, and you should be able to figure out how to properly tune the antenna.

Jul 07, 2009 | Cobra 25 NW LTD 40-Channels Base CB Radio

2 Answers

Cobra 29 ltd classic ant light


Your SWR is probably NOT fine. You need to use an external meter if you have had work done to the radio. Especially if you have had a swing mod done to the radio. When you do this, the dead key of the radio is lower then the calibration knob on the radio can adjust for. It will always come up lower then it actually is.

Your radio might have been fine before the work was done on it because it was putting out very little power. Now you are most likely putting out 50 watts or more. Big jump from 4 watts.

When your raise the power in a radio, you will notice more when the antenna is not properly tuned.

In most cases with a stock CB, even when the antenna is not even near tuned, you will get a reading less then 1.5 anyway.

the more power you put out, the more important it is to have a good match.

But an external SWR meter, and check it. be careful if the ANT light is on.

You might also want to check your coax, connections to it, and your antenna for anything wrong.

Apr 22, 2009 | Cobra 29 LTD CB Radio

2 Answers

Cobra 29 ltd classic antenna calibration ??


Wow. That's not at all a solution to what this guy is asking. And why all the caps??

The one point jm77437 has that is correct is that you do not set the radio, you set the antenna. The rest is blah blah.

Here is how you tune your antenna for you radio. First off it depends on what kind of antenna you have. most fiberglass antennas have a tunable tip to adjust the height of the antenna. Metal whips either have a collar at the base that the whip will either slide up or down in to adjust the height. The other type of metal whip's you have to physically clip to shorten the antenna, you must be careful with this type because once its clipped, that's it. You cannot add what you cut off.

I am going to give this example using a metal whip with an adjustable collar.

First after your radio is hooked up in the vehicle, drive to an open lot. Buildings and other structures can cause extra reflection. turn to channel 1. Flip the meter to CAL. Key the mic without talking. Now turn the CAL knob up until the needle reaches the little upside down triangle all the way to the right marked CAL. Now you have just celebrated your radio for your setup to measure you SWR. Now while still holding the key, flip the meter switch to SWR. The needle will move, and where it stops is your SWR reading. The lower the better. Anything under 1.5 is considered really good. But still, the lower the better.

Make note of what your SWR was on ch 1.

Now flip to channel 40. Repeat the SWR process. You must recalabrate each time you take a reading.

Now like jm77437 said. If your SWR reading is higher on 40 then 1, then your antenna is too long, and you must make it shorter. Loosen the collar and lower the antenna in the collar 1/4 inch at a time. check the swr each time you adjust the antenna.

If your SWR reading is higher on channel 1, then your antenna is too short. You must make your antenna longer. Do this by loossening the collar and pulling the antenna upward in the collar 1/4 inch at a time, again checking the swr each time you adjust the antenna.

What you want to achieve is having the same SWR reading on channel 1 and 40. then you have the best match you are going to get with that antenna.

If your swr is under 1.5 on all channels, you don't need to fuss unless you are a perfectionist. then by all means go ahead.

If your reading is higher then 3, or your ant light comes on, something is really wrong. Make sure your antenna is connected all the way, and the coax is not damaged.

Its important to have an appropriate SWR because if you do not, you are reflecting too much signal back into the radio, and eventually you will burn out your final transistor, and your radio will be toast.

Some tips: make sure you check the swr with the doors and windows shut. Make sure you are in an open lot. Remember to calabrate ecah time you take a reading. If you have had your radio peaked by a radio shop, and they have lowered your dead key, or have done a swing modification, then the meter in your radio will not work when taking an SWR reading and you will have to use an external meter.

Mar 12, 2009 | Cobra Radio Communications

3 Answers

Cobra 29 ltd classic antenna calibration ??


You should not calibrate the antenna before you install it on the car!! the antenna needs to be calibrated on the vehicle that it is going to be on. Type of vehicle, different mounts, and many other variables can change the amount of reflection you will get.

j0hn9999 did a much better job but left some info out.

Take your SWR readings on channel 1, then on channel 40.... NOW, if your SWR is higher on ch 40 then ch 1, then your antenna is too long and it needs to be shortened. Refer to the antenna instructions on how to shorten the antenna.

If your SWR is higher on ch 1 then on ch 40 then your antenna is too short. You must lengthen the antenna. Again refer to your antenna instructions on how to lengthen your antenna.

You must calibrate each time you take a reading.

Make sure your doors and windows are shut when taking a reading

Make sure you are in an open lot when taking a reading as buildings, trees and other structures can cause reflection and give you an inaccurate reading.

If you adjust the length of your antenna on another vehicle and then put it on yours, the SWR will be off. It will need to be tuned again.

An external meter is better then the one in the radio, but will need to be hooked up in the vehicle you have the antenna on.

If you are not running any kind of power, or do not have a swing kit installed, and the radio is stock, the meter in the radio is more then enough to get a correct SWR reading.

Sep 27, 2008 | Cobra 29 LTD CB Radio

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