Question about Cobra 29 LTD CB Radio

1 Answer

Cobra 29 I am a student at Reading High Vo Tech, I am doing a project on the Cobra 29, with my project I am trying to get 30 watts out of this radio. I've seen a few videos on YouTube with the Cobra 29 doing 30watts, but there are none that show how they got 30 watts out of it. I was hoping someone who works with Cobra tech support could help me figure out how I can get 30 watts out of this radio so I can complete this project and get a good grade for it. Thank you, Brandon

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  • brandonkieta
    brandonkieta Feb 22, 2012

    I need this project done by next Friday

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1 Answer

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  • Master
  • 1,212 Answers

Essentially what is done is replace the RF output transistor with one that can handle the 30 Watts output. Since you are not going to achieve it with higher B voltage, you have to modulate more current, and the bias voltages adjusted to accomodate the different characteristics of the new of the new final. Then the radio is checked to make sure the tank circuit is still in tune.

This is the basic outline of how to do it in a manner where you actually learn hands on, and apply what you should already know.

The alternate method is to install a linear amplifier. A 10 meter linear can usually work with only slight modifications.

BTW. the common search engines are worthless for finding radio mods. By design- they are oriented to a controlled marketplace.

Posted on Feb 25, 2012

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Posted on Jan 02, 2017

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SOURCE: 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.

Posted on Apr 24, 2009

One Wire
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SOURCE: echo on cobra 29

When you purchase an echo board, the instructions come with them.

If you need any help, don't hesitate to email me at rollincbmods@yahoo.com

Dean Pitts
Rollin CBs

Posted on Aug 31, 2008

  • 773 Answers

SOURCE: not enough watts

All he is asking for is this...

Find VR4. Its near the big transformer. Turn it all the way to the left. That is your AMC. that will turn your modulation all the way up.

If you have a power meter you can raise your dead key, or carrier signal as raising the modulation only effects your swing.

If you don't have power meter, then don't mess with it. Increasing the modulation will be a big improvement.

If you do have a power meter then here is what you do. Find L12 near the final, is near the heat sink in the little space near the transistor. that is your final. Turn this out, to the left, with the radio keyed until the needle stops moving up. don't turn it out any more.

***** NOTE IMPORTANT *******

Do not do this with no antenna hooked up, or without a dummy load. You will blow up your final. You can never key the radio with out a 50 ohm load on the radio.

You can make a simple dummy load to do this inside instead of out in your vehicle. Take a CB coax and 5 150 ohm resistors. Hook the 3 ends of the resistors together and solder them, and do the same with the other side. then solder on end to the center piece of a coax, and then to the out side piece. that will give you a 50 ohm load when you connect it to the radio. If the Ant light goes on, stop right away you did something wrong.

You will also need a power supply. If you have an old computer, you can use the power supply from it to power the radio. Yellow wire on one of the power supply ends to the red wire, and the black can go to either of the black wires.


If you are not sure, just increase the modulation with VR4. that will make the radio swing to about 20 - 25 watts.

Posted on Feb 19, 2009

  • 773 Answers

SOURCE: 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.

Posted on Apr 24, 2009

  • 6 Answers

SOURCE: how do you tune and peak a cobra 29 ltd classic

i would highly suggest you take it to a cb shop to get a cb tuned and peaked. before you do that though, make sure you have a good antenna system. a good antenna will have a much greater effect on your cb than tuning and peaking. as far as output, who knows? it all depends on the skill of the person doing the tuning. be warned that any output over 4 watts is illegal and you could recieve hefty fines if caught with an illegal radio.

Posted on Sep 24, 2009

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Got a cobra 29 ltd classic dead keys 10 watts and swings back to 6 watts on an external meter any answers


Hi you have to make sure your antenna has 1:1 SWR reading improper use of antennas deplete the Effective radiating Power of Transmitting equipment such as the CB radio.

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The 29 can be altered to increase modulation and turned down in power to match it to amp for increased output of power.

Set to dead key a watt or so with a 100 watt amp it would dead key low and swing to 80 to 100 watts pep.(peak envelope power)

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How do you adjust the max power L14 in a cobra 29 ltd classic ?


First off, NEVER do any adjustments without a watt/swr/mod meter and at least a 50 ohm dummy load. L14 is a coil with a carbon slug in it. it is sealed with wax. To adjust it you must remove the wax. After doing that, make your adjustments with a plastic tool. Key the mic, adjust the slug until you get the highest reading on the watt meter. Then replace the wax. NEVER exceed 4 watts. To do the job correctly, you need to adjust L14,L13,L12 in that order.

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Cobra 29 ltd classic has no key watts


Not sure why you removed a resistor, but apparently it was needed in order to make the radio transmit properly. Put the resistor back in, or a new one of the same value. If you don't know the required value (because it was fried, etc.), I'd recomend bringing it to a shop, as there is most likely something else wrong with the unit.

If you really want to try and repair it yourself, and don't know the value, check out the schematics at the link below; just be sure that you are looking at the schematics that pertain to your radio, as there are a number of different versions of the Cobra 29.

Cobra 29 - CBTRICKS.COM

Oct 27, 2011 | Cobra 29 LTD CB Radio

1 Answer

Well ive got a cobra 29 with a RF85X installed on it, it worked great for awhile then all of a sudden it stop transmitting took it to cb shop and repairman found the problem was a cap or diode which should...


Have you checked the SWR's.. also some caps help with the roll off of stray emissions . hopefully he took out the right one. also if you have low amperage going to the radio. it will cause problems. normal cobra 29 2-5amps and the factory pwr cord is adequate for that amperage now your pulling 80watts + make sure you have more amps to handle it. watts/13.8volts=AMPS needed. soo say if your radio is doing 100w/13volts you will need 7.7amps basically in theory.. amps- good grounds- good swr's that shop should of checked your antenna for free.. we do here in texas.

Jan 04, 2011 | Cobra 29 LTD CB Radio

1 Answer

I LIKE TO MAKE MY COBRA 29 HIGH POWER TALK A LONG WAYS HELP ME


Get a "swing kit" installed for about $20
Buy a power mic
Have the audio maxed out (simple turn of the VR4)
Have money to spend???
http://cbradio.auctivacommerce.com/IN-STOCK-EKL-POWER-BAND-RFX-75-P429725.aspx
Go there and for about $100 your Cobra will do 100 watts or a little more
"WILDCAT" IN LAURELVILLE OHIO
35 YEARS IN THE CB WORLD!!!

Dec 28, 2010 | Cobra 29 LTD CB Radio

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

Cobra 29 modulation modification


did you make sure the caps stripe is facing the back of the radio? If not, its the wrong way.

Also, don't use a 1/4 watt resistor because it will get too hot for it to last. use 1/8th.

changing the cap size will not change output, however it will change the tone. Bigger the cap, the deeper the tone of audio.

to be honest with you, high output mods are worthless in these radios. they are fine with out them. mosfets are unstable and are very dirty transmit finals. As well if you are planning to use a linear you may hit it too hard unless its a high drive, in which case you will need more then 35 watts swing to drive it fully. A stock cobra 29 that has been peaked and tuned, then the swing mod put in, 220uf e cap and 100 ohm resistor, which should give you about 2 watts, should swing to about 27 watts, and kick an amp in the pants.

I run a cobra 29 in my blazer with a dave made 5 pill, and I key on 6 pills and I near keyed on a 2x8. very close. All that I have done to the radio is peak and tune, (of course I have a few tricks with that up my sleave which I don't usually share with just any one.) and variable power, wich will control the dead key, which is basically a varible swing kit. I run it just under 2 watts, just enoug to get a 125 watt dead key out of the amp. The amps swings over 920 watts.

any more swing from the radio will beat up the pills in the amp.

Jan 06, 2010 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29 cb calibaration


bad ground but the time of day is also a factor. If you are trying to talk when there is a lot of ground noise you may not get out more than a half mile or so.

Jul 29, 2009 | Cobra 29 LTD CB Radio

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