Question about Cobra 29 LTD CB Radio

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I have a cobra ltd 29 bt hooking to a 102 inch whip and cannot get m swr readings down under 3 or it will go up higher then the calibrate triangle instead of down. my antenna is mounted with a gumdrop mount to a peice of aluminum to the tool box which is screwd into te bed and grounded out.. my cable is cut to the right length with no twists or bends in it anywhere. let me know what u guys think. need fixed ASAP

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  • Sounds to me like you need to check the connectors and connections on that coax. A cobra29 and a 102" whip is a simple enough set up and should not produce that high of SWR unless the coax or the connectors on the coax are pretty messed up. Also i recommend putting an SWR meter in line.
  • The meters on them Cobras can be accurate sometimes but I trust an inline meter much more.
  • Ground it again to make sure.
Regards, Tony

Posted on May 18, 2011

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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

How do I fix SWR spikes?


For CB radio that operates in a relatively narrow bandwidth, you should be able to obtain "perfect" SWR readings for all 40 channels. That would be a reading of 1.1 : 1 or less.
The rule of thumb goes like this: if SWR is HIGHER on HIGHER FREQUENCY (Ch. 40 is higher than Ch. 1) then the antenna whip is too HIGH (too long/tall) therefore it must be shortenned. And vice versa.
Trimming the length requires patience especially when the reading has reached 1.5 : 1 or lower/better. Make a 5mm trim each time and then measure SWR then continue trimming until you are satisfied with the results.
The spike must be contributed by faulty electronic components inside the radio. The radio must be checked by a technician. But before you do that, trim your whip first and see what happens. Ideally, the length of the coax cable must be trimmed as well. But, since we don't live in an ideal world, we can ignore that for the time being. Goodluck. es

Jun 10, 2013 | Radio Communications

1 Answer

I have a cobra ltd 29 cb radio. I bought a 102 inch whip for it now when I key up my mike I hear my self threw my speaker and I can't transmit what's the deal


its shorting against the "Ground" sounds like. Check your mount on the 102 inch whip, also check coax, get you an SWR meter from RADIO SHACK , check it should be 1.1 to 1.5, if its 3.1 to 4.1 it has a short. Hope you get this fixed....Do not transmit with this short; or you fry the finals.

May 16, 2011 | Cobra Radio Communications

1 Answer

I have my cobra hooked up to a 5 foot fiberglass antenna an when my friend goes down the road I can only hear him for a mile but when he is sitting next to me he is picking up from 40 miles away with him...


Use a 8.5 feet(102 inches) That would be the size of this whip. One thing to do put it up high in the air in 15,30,45 feet lengths. Have heavy grounding like 4 metal rods drove into earth 6 ft. use a tower and also ground it to a big metal filing cabinet or water pipes. I found that your Electric meter box is grounded real well. Use big low loss coaxial 50 ohm in the lengths 9,18,27,36. Your hearing is through sometimes ground planes. Lets say you use a tower or Tv pole 30 feet. Mount your 102" in. whip on top- seperate it from 4 ground prongs by rigging PVC pipe in between. Make 4 Ground planes about 5 feet go out North,East,South,West. Run 30 feet of coax to your house. It should pick up better an transmit better. Check SWR (1.5 or so) SWR Varies 1.1-2.1 ratios. I never had no problems talking on mine 5 to 30 miles away. Turn up receive inside radio. Its near front ; may be white variable or chrome with screwdriver slot. Take speaker side off and look near left handside front when radio is upside down.

Apr 04, 2011 | Cobra 29 LTD CB Radio

1 Answer

I want to calibrate my cobra 29 NW Ltd. Classic


Calibrate For SWR (Standing Wave Ratio) http://www.cbtricks.com/radios/cobra/29ltd_bt/graphics/cobra_29ltd_bt_om.pdf
The CAL is only to calibrate meter for a swr check of you antenna system it does not calibrate radio.

Jan 11, 2011 | Cobra 29 LTD CB Radio

1 Answer

I've got a Cobra 29 with WX and BT, the antenna light comes on, the swr meter barely moves and it doesn't seem to send or receive, still gets weather. May have been run with a bad antenna, got a new...


Please make sure you are tuning the antenna correctly.



It is important to tune your CB radio antenna to the proper length. The length must exactly match the wavelength of the frequency you transmit on. Or be really really close.

All Cb antenna's have a way to adjust the length of the antenna. If it's a mag mount, the metal whip can be slid in and out of a metal collar. Usually a set screw. If its a fiberglass whip, the way to tune it is on top. It either has a small metal rod with a set screw to adjust the length, or it threads in and out to adjust length.

Either type you have it will need to be adjusted for proper length. Here is how to tune the antenna to lowest SWR.

Some radios have a built in SWR meter. Some do not. If yours doesn't have an SWR meter, then you have to use an external SWR meter. Radio shack carries one, and you can find them cheap on ebay.

If you have a built in SWR meter or external, the procedure is the same:

1. Turn the radio to CH 20.(This is the center of the band.)
2. Switch the meter switch to CAL. (CAL stand for calibrate.
3. Key the radio. (Important. Do not talk while keying the radio.)
4. turn the CAL knob up until the meter hits the CAL mark.
5. Now while still keying the radio flip the meter switch to SWR.

Where the meter falls after that point is you SWR reading. If its above 3, that is real bad. 2 is not gonna kill your radio but its not the greatest. 1.5 and under is a good place to be, but the lower the better.

If your SWR is high, Here is how to find out if your antenna is too long or too short.

1. Turn to CH 1
2. Repeat SWR procedure. You must calibrate every time you do it.
3. Remember the SWR reading.
4. Turn to CH 40.
5. Again repeat SWR procedure.
6. Compare the reading between CH 1 and CH 40.

Now if the SWR is higher on channel 1 then channel 40 your antenna is too short. You must make it longer.

If the SWR is longer on channel 40 then on channel 1, then the antenna is too long, you need to make it shorter.

Make height adjustments about an eight inch at a time, and take reading each time.

once the SWR is significantly lower and the reading on channel 1 and 40 are about the same, you a about matched. At this point turn the radio to the center of the band, channel 20 and take an SWR reading.

You should now have a low SWR reading, 1.5 or under. If you are 1.5 or under, you are good to go.

If you cannot get the SWR to an appropriate level, there may be an antenna problem.






Now: If you have adjusted the antenna properly and you still get the antenna warning light, then the antenna warning circuit may be out of whack. Use an external SWR meter.

You may also be getting common mode current. Its when RF comes down the outside of the coax. If the swr goes up with modulation then it's common mode.

Here is how to stop common mode.

As close to the antenna as you can while still inside the vehicle, take about 6 to 8 inches of the coax, and coil it up into tight even coils and secure into shape with electrical tape.

This is an RF choke, and will stop the common mode current.

If all other radio's are fine and no ant light come one, and are all showing low swr, then turn VR6 back to disable the ant warning light. "only do this if the ant light comes on when SWR is lower then 1.5 and does not swing up with modulation showing that the ant warning light is miss aligned.

Nov 07, 2010 | Cobra 29 LTD CB Radio

1 Answer

I lost my manual and I don't know how to calibrate my CB its a cobra 29Ltd chrome edition


It is important to tune your CB radio antenna to the proper length. The length must exactly match the wavelength of the frequency you transmit on. Or be really really close.

All Cb antenna's have a way to adjust the length of the antenna. If it's a mag mount, the metal whip can be slid in and out of a metal collar. Usually a set screw. If its a fiberglass whip, the way to tune it is on top. It either has a small metal rod with a set screw to adjust the length, or it threads in and out to adjust length.

Either type you have it will need to be adjusted for proper length. Here is how to tune the antenna to lowest SWR.

Some radios have a built in SWR meter. Some do not. If yours doesn't have an SWR meter, then you have to use an external SWR meter. Radio shack carries one, and you can find them cheap on ebay.

If you have a built in SWR meter or external, the procedure is the same:

1. Turn the radio to CH 20.(This is the center of the band.)
2. Switch the meter switch to CAL. (CAL stand for calibrate.
3. Key the radio. (Important. Do not talk while keying the radio.)
4. turn the CAL knob up until the meter hits the CAL mark.
5. Now while still keying the radio flip the meter switch to SWR.

Where the meter falls after that point is you SWR reading. If its above 3, that is real bad. 2 is not gonna kill your radio but its not the greatest. 1.5 and under is a good place to be, but the lower the better.

If your SWR is high, Here is how to find out if your antenna is too long or too short.

1. Turn to CH 1
2. Repeat SWR procedure. You must calibrate every time you do it.
3. Remember the SWR reading.
4. Turn to CH 40.
5. Again repeat SWR procedure.
6. Compare the reading between CH 1 and CH 40.

Now if the SWR is higher on channel 1 then channel 40 your antenna is too short. You must make it longer.

If the SWR is longer on channel 40 then on channel 1, then the antenna is too long, you need to make it shorter.

Make height adjustments about an eight inch at a time, and take reading each time.

once the SWR is significantly lower and the reading on channel 1 and 40 are about the same, you a about matched. At this point turn the radio to the center of the band, channel 20 and take an SWR reading.

You should now have a low SWR reading, 1.5 or under. If you are 1.5 or under, you are good to go.

If you cannot get the SWR to an appropriate level, there may be an antenna problem.

Oct 21, 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

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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