I have a cobra 29 with a rfx-75 on the back and there is a swing kit in the radio. I use a 2 pill fatboy as well. When i got the radio it had a 5 watt dead key. I lowered the dead key to a 2 watt dead key. Well found out that with a rfx-75 when you talk on it and the rfx gets warm the dead key will drop. Since i set it to a 2 watt dead key it dropped to no dead key. I reset it to a 4 watt dead key so i would drop to a 2 watt dead key. Well know i can turn on the radio and talk and there is no dead key and somertimes ther is. Any ideas on what is causing this problem?

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.

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.

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.

SOURCE: cobra 148fgtl low power on am/ssb no swing all finals ok

try adjusting the L36,L38 to the highest reading on the external meter and then adjust VR10 TO 4 watts. If this doesn't cure the problem, you have a weak final transistor. Good Luck

SOURCE: cobra 29 classic "swing kit" ?

A swing kit is nothing more then a Cap and a resistor. There really isn't a different way to do a swing kit, unless you do variable power, which you don't need unless you are going to run a linear, and even then you can just set the dead key with a swing kit.

you need a watt meter, preferably one that reads peak and average watts. If not, average will be find.

Open the bottom cover of the radio. Hook the radio up to the watt meter, use a dummy load or have it hooked to the antenna. Never key the radio with an antenna or a dummy load.

Find VR4. Its toward the back right of the radio. Turn it all the way to the left. That increases your modulation.

Next find L14. it is at the back in front of the final resistor. While making a steady sound into the radio, just make an ahhhhhhh noise. Back the slug out of the tank until the needle hits peak. Don't move it out any more or you will over bias the final.

Now you will need a 220 uf electrolytic cap, and a 100 ohm 1/2 watt resistor, both of which you can get from radio shack. (this is your swing kit.

To the right of the tank slug is a jumper maked JP36. Us soldering wick to remove the solder and pull out the jumper. Now put the cap in it with the stripe facing the back of the radio.(that is very important. the other way you will blow the radio.) Solder it in place and cut the extra leads off. Now on the back of the board were you soldered in the cap, solder the 100 ohm resistor in between the 2 points.

The amount of resistance determines you dead key. you will be at about a 2 watt dead key which is good for swing and if you want to run a linear. The higher the resistor the lower the dead key, and the lower the cap, the higher the dead key.

That is your basic peak and tune with a swing kit.

Testimonial: "wow ! good info .......thnx"