I have a cobra 150 gtl dx cb radio. my reception and transmition is not at peek performance. can you help me please? i have tried everything i know to do.
If this radio has been peaked and tuned already, and it is not in need of a full alignment, then it's most likely the antenna.
Your antenna is everything. You need a good antenna, and it needs to be tuned to the lowest SWR.
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 20, 2010 |
Cobra 150 GTL DX Base CB Radio