SWR Low on all channels - Cobra 29 LTD CB Radio

you have no power because your radio is not tuned to your antenna.You get a new radio and put junky coax and a decent antenna and you expect it to work right. Get 75 ft of rg-213 and you will see a change.

Tune your antenna. If he took the metal whip out of the base, then he messed the tuning all up.




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.

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.

Your antenna is not tuned for Lowest SWR. The higher the SWR the less power you put out.

It needs to be tuned to the center of the band. Channel 19 or 20. an SWR of 2 is not that good. You should not go over 1.5. Idealely it should be as low as possible. My antenna is tuned so that my SWR is 1.0 on every channel.

So on channel 1 your SWR is high, so it puts out less power. Some what better on channel 20. And your SWR is lowest on channel 40, thus it gets out better.

You want to get the SWR on channels 1 and 40 the same. You need to know whether or not the antenna is too long or short.

Tune to channel 1 take a reading. Take note of it. Then do the same one channel 40.

If the reading is higher on 40 then on 1 your antenna is too long and you need to make it shorter. if its higher on 1 then on 40, its too short so make it longer. When you get to the point when the SWR on 1 and 40 is about the same, you about as good as you are going to get with the meter in the radio, and you will see that on channel 20 your SWR will be very low, and it will be your best channel, and you will also see that you put out about the same wattage on all channels.

On some radio's that are bone stock with a stock mic you have to speak directly into the mic and not mumble;as for your swr if it's high on channel 1 and low on channel 40 you need to shorten your antenna if it's low on 1 and high on 40 you need to lengthen your antenna.Good Luck. Dan

not necessarily. it may be electrically short. if the swr is higher on channel one than it is on channel fourty, your antenna is electrically short. if the swr is higher on channel fourty than it is on channel one, your antenna is electrically long. no matter what anyone says, all antennas are tunable. just cut the shielding back at the top of the antenna and adjust if necessary. if it is a steel whip, it should have a set screw at the bottom. if you still have problems with high swr, ground the mount to your vehicle. if you still have high swr, you might have to try a non ground plane antenna.

have you checked the coax connectors? It's gotta be a bad connector,damaged coax or a defective antenna. Careful--don't test "too much" or you'll burnout the final amp!

This is a common problem in CB's. You can either get the radio tuned properly or tune the antenna. Sometimes the CB will put out more power on a channel than is needed and this could end up in a damaged radio. You can get the radio tuned to prevent the RADIO from high SWR, or you can tune the ANTENNA so tha antenna will better suit your CB's power.

Hope this helps!

The lower the SWR the better!

SWR is actually a ratio, e.g. 5:1, but generally speaking only the first number (5 in this case) is written as the second is always a 1. The lowest SWR you can get is 1 (1:1). So if you've got 1.5, that is very good.

Hope this helps,

Matt

Hi,

Based on your post/description:

1. how do i set the swr
Normally SWR are calibrated on your operating channel (where you usually stand-by). This is to maximize transmit power and receive sensitivity. To set SWR, switch to channel of your choice, switch SWR control to CAL, key or press PTT, while pressing PTT rotate ADJ knob until max deflection of needle on meter, release mic, switch control to SWR, key/press PTT, needle reading/deflection is SWR for that channel.

I would suspect that your SWR will vary from your current 1.4. This is because you have too big excursion of channels (240 channels).

2.reading a 1.4
This reading is good enough and should do. However as earlier stated, you seem to have 240 channels which would mean that your radio + antenna moves in a wide bandwidth and since the antenna tuning is affected by frequency, your SWR will also be affected by channel.

Best if you can further lower it down.

3. some cb cant get me
This is because the standard CB radio is only 40 channels. The next would be a 80 channel and then 120 channels.

4. is it my radio
Yes, you have a wide coverage radio almost an extended 10 meter rig.

5. do i have to set my radio on high or low to set my swr
I will assume you are referring to power output, set it to HIGH when doing SWR calibration

Hope this be of some help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.