Question about Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

148 gtl Placed workman b-100 in attic, I can not tune antenna as swr swings to the right on transmit

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  • Mechanic688
    Mechanic688 May 11, 2010

    What length of coax are you using with that antenna?
    I think they are tunable by changing the length of the coax,,, correct me if I'm wrong guys. I tried looking for a chart, but right now I could not find it.
    Mechanic

  • SHARCNET-USA
    SHARCNET-USA May 11, 2010

    Is the antenna clear from any metal objects such as vent pipes, electrical conduit, etc. that can affect the antenna's SWR? I agree, an external SWR meter far exceeds the performance of the one in the radio. Also, trying a 50 ohm resistive dummy load connected on the output of the SWR meter will let you see how well the radio is working into a good load. The goal is to get a reading while using the antenna to be as close to the reading you would get on a true 50 ohm resistive load.



    - Jim

  • Dean Dishman May 11, 2010

    Are you using the radios meter?? You need an external swr meter the meter on the radios are not very accurate.The wokman B-100 needs no ground plane to work But you need a decent meter to set it .Let me know what you find out ...Thanks Dean

  • brian c
    brian c May 11, 2010

    What antenna setup are you using?

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Hi Benimur, the only reason I chimed in on this topic is that years ago my CB shop did some testing on that antenna and a few others from Workman using a MFJ 269 analyzer. I seem to remember there being a coax chart available for CB freq's and also 10 meter freq's. There is no tuning adjustment on the ant itself, so there has to be some way for adjustments,, thanks, Mechanic

Posted on Feb 07, 2008

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Hi,

It would seem that you posted twice. Here is the link to your other post.

If I may add to Mechanic688, sharcnet, chiaflub67 and Nitrotrike's postings (with their indulgence), below is a copy of my reply to the other post....

"I read through the specifications of this antenna and you were right in posting "no ground plane, no tune". Still, there are only three (3) possible reasons why the SWR would be high:
1. Cable/connector - loose, cold solder or improperly terminated;
2. Antenna - tuning and/or ground plane; and
3. Radio has been highly modified or defect in final stage.

Corrective procedures would call for:
a. verify that the coaxial cable is properly connected to the PL-259 connectors. You may need to use a continuity tester (or a DVM) to do so. Pls pay particular attention to the braided shield/grounding, they should be real tight/soldered good to the casing of the connector. Of course the cable should be 50ohms RG8 or 58 with thick shielding.
b. as stated, the antenna doesn't need to be tuned then there's nothing that can be done since there is no provision for such, however, even if the specs says no ground plane needed, there is something you can try. Install a ground plane. this could be done by attaching 2 lengths of big gauge ordinary wire to both sides of the metal bracket of the antenna. They have to be 8' 7" ~ 9' long. It may help you further to install a grounding strap again from the metal bracket to any grounded metal portions of your house such as the plumbing.
c. radio problem would be unlikely if it is still stock."

Regards all.

Posted on Feb 07, 2008

  • Louie  Role
    Louie Role Feb 07, 2008

    Oops, the link did not work, here we go....

    Here is the link to your other post.

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2 Answers

Cobra 148 gtl d has problem transmiting with covers off. trying to tune radio up. was thinking I need to ground the chasis


I would say a bad or cold solder joint on board somewhere. Bad quality control. Might flex radio chassis slightly while keying? A tooth pick and hours of probing around switching area on board and the pa section till problem found.

Oct 25, 2012 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

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

1 Answer

Have a cobra 148 gtl cb/ssb. It is brand new. I hvae it hooked up and have tuned the antenna using the swr meter on the cb. I habe channel 1 and channel 40 metting at about 1.6 swr. I have what appears to...


Hi, my name is John. Welcome to FixYa. Check your antenna, you need to set it with a real SWR meter, pick one up at any near-by CB shack $10.00. Thanks for choosing Fixya...John

Jul 22, 2010 | Cobra 148 GTL 120-Channels Base CB Radio

4 Answers

Have not used my cobra for some time ...sine someone need my K40 antennae more than me. Just put it back in service with a new magnet mount 36 inch - can send and receive in USB and LSB ....can here in the...


Center the antenna on the vehicle, then check the SWR on channel 1 and channel 40.
with the switch in CAL position, key radio and use the swr/cal knob to set the meter so the needle is just touching the end of the red area on the right-hand side of the meter.
Once calibrated, unkey and switch the switch to SWR and key up again. The lower the reading, the better. If the SWR is Higher on 40, the antenna needs to be shorter.. if its higher on 1, then the antenna needs to be longer.

if it dont transmit period on AM, then there's an internal glitch :)

Jan 24, 2010 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Have a new cobra 148 gtl took out of box no transmit or recieve


make sure that your [swr] hadn't changed or went higher than a 1.5, anything higher will interfere with your tranmitting an recieving. other than that with out being there to see an hear your radio this would be the first place to start.

Apr 25, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Just bought a cobra 148 gtl dx cant get a antenna outside just wondering the best indoor antenna i could use thanx


There really is no good indoor antenna.

You need to understand how the radio works and what reflections is.

Your radio radiates RF energy from the antenna. If the antenna is not the correct length for the frequency you are transmitting on then the signal will be reflected back into the radio and burn up the final transistor which is the lifeblood of the radio. This is your SWR or standing wave ratio.

The antenna has adjustments to correct this, and it is a simple process.

Here is what will cause you trouble. When you measure SWR in a car, you do it in an open lot, and not in a closed in area, because structures such as trees and buildings can cause reflection as well. If you inside a garage, then you will get a lot of reflection.

Beings you will be inside with the antenna, you are trapping the RF in a room, and it is reflecting most of the RF. Your SWR's will be really high, and hurt the radio.

Indoor antenna's are made so that it compensates for this, but your signal will be very weak, and your receive will be garbage.

Here is something you can do to get the antenna outside.

First get a real base antenna, like an antron 99, its good for the money.

Get 2 lengths of galvanized pipe 2" by 10 foot and a 1/4 inch thick steal plate. weld the pipe to the plate so that it will stand off it. Make sure its all the way off to side. connect the 2 pipes together, put the antenna on the end of it, and stand it up. Park the wheel of a car or truck on the plate. This will stabilize the pole.

Now you have a temp antenna tower you can take down and put back up easy.

I wouldn't go higher then 20 feet.

Apr 19, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

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

Feb 06, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

6 Answers

Saturn workman b-100


Hi,

I read through the specifications of this antenna and you were right in posting "no ground plane, no tune". Still, there are only three (3) possible reasons why the SWR would be high:
1. Cable/connector - loose, cold solder or improperly terminated;
2. Antenna - tuning and/or ground plane; and
3. Radio has been highly modified or defect in final stage.

Corrective procedures would call for:
a. verify that the coaxial cable is properly connected to the PL-259 connectors. You may need to use a continuity tester (or a DVM) to do so. Pls pay particular attention to the braided shield/grounding, they should be real tight/soldered good to the casing of the connector. Of course the cable should be 50ohms RG8 or 58 with thick shielding.
b. as stated the antenna doesn't need to be tuned then there's nothing that can be done since there is no provision for such, however, even if the specs says no ground plane needed, there is something you can try. Install a ground plane. this could be done by attaching 2 lengths of big gauge ordinary wire to both sides of the metal bracket of the antenna. They have to be 8' 7" ~ 9' long. It may help you further to install a grounding strap again from the metal bracket to any grounded metal portions of your house such as the plumbing.
c. radio problem would be unlikely if it is still stock.

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

Good luck and kind regards.

Feb 06, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

No transmit or recive but works on pa mode


does this radio have freq? if so you could have turned on causing
a miss alignment with antena.. check all the switches move into different positions and keep keying up, good antena connection?
swr?
tony

Dec 03, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

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