Question about Cobra 148 GTL 120-Channels Base CB Radio

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Saturn workman b-100

SWR is way too high using b-100 in attic with 148 gtl.This is a no ground plain antenna with bracket screwed into a wooden truss.Is there any way to tune the antenna as I thought no tune was needed.

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I just bought this antenna and i saw that swr was off the scale so i was thinking and thought of trying a ground on the bracket of the antenna and when i did that the swr's were totally flat. When i did that i called my buddy and told him to let me know what the signal was with this antenna and he said it was like 91/2 pounds for signal and that was with it in my bedroom. so i would just put a ground wire on the bracket andyou would be good.

Posted on Jan 18, 2009

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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.

Posted on Feb 07, 2008

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Remember keep everything in lengths of 3 for good swrs

Posted on Feb 07, 2013

Spend 20 dollars more and get a 12 foot stick

Posted on Nov 08, 2008

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Hello everybody,try to use a 28 metres of coaxila cable rg58 and cut it untill the swr go down.I do that and the srw of my antenna is 1:1,2 on 27.285MHz till 27.585MHz.
73 and good luck
rick

Posted on Feb 02, 2009

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I had this same problem; I was using RG-8 with homemade connectors. My SWR was off the chart. I picked up 50' of RG-58 from Radio shack and the SWR needle hardly moved. So I guess I have to get better at soldering RG-8 connectors.

Thanks for the tip, its much appreicated.

Posted on Sep 30, 2008

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ok, you have a high SWR.. this is what you can do.. you're gonna need to check the Radio's coax connection to see if it's loose on the Radio itself.. you're gonna have to open the Radio cover on the speaker side.. now go look at the connections on the pc board itself and see if there is a possible broke connection.. one is pcb ground, and one for the center. also, you might want to get a phillips head screw driver and gently tighten all the screws on the pc board. becareful going in there.. after this said and done, check the antenna connector itself to see if it's loose. if so, then you're gonna have to a pair of pliers to turn the nut on the inside while you use wrench to hold it in place on the outside.. now you're ready to test the radio.. don't put the cover on just yet until you see the results. set up your SWR Meter to the Radio and then set up the dummy load and do a SWR Test. if the reading is good, then the Radio is all set.. now for the Antenna.. you said that it's all new, but regardless you need to test it too.. check both ends of the cable and do a condinuity test.. get a ohm meter that has an audio sound. this will help you.. set the meter to ohms/conditnuity.. then short out the probes to get a ZERO reading/audio sound.. now take one end of the of the cable and put the probes on the connector.. one probe for the outter ground shell and the other probe to the center pin connection. if you see a ZERO reading or an audio sound, that means you have a short in the cable.. another way is to do it end to end.. put one probe on one end of the cable, and the other probe on the other end.. test the ground side first.. if you get a sound or a ZERO reading, that means you may have a short in the cable itself and may requier to remove the connectors.. some cases you might have to replace them.. remember to calibrate your meter when testing let me know how it goes.. I'll continue to help you.. you can contact me on Facebook.. https://www.facebook.com/pages/ANR-Communications-Repair/136358796473669?ref=bookmarks Good Luck..

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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

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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.
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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

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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.

Jan 31, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Cb equipmebnt


Hi,

Connect the INput of the amp to the TX out of the radio. Connect the OUTput/Ant of the amp to the INput of the meter (SWR/Power). Connect the OUTput of the meter to the cable that leads to the antenna.

With this arrangement, you will be able to measure the SWR of the antenna and power output (of the amp) going to the antenna.

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

Good luck and kind regards.

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