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.
Posted by Steelwheel on
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
The radio has good tx audio and pa audio, so the audio chip is working. I can create audio by do a "finger resitance" across the pcb. any ides where to look? everything on the radio is good except rx audio. Even took anther 148 and jumpered between the red wires on vloume, the radio would create sound from the other radio. RX does work, needle moves and you can pick up some sound by "fingering the pcb..... cobra148 gtl malaysia pcb 1995 build
Posted by Charles... on
No audio out / low audio out....This is a constant problem with the COBRA 148 gtl....to get a good level of volume replace the
electro caps ...start around the two speaker wires and work back from there. I'm in the process of rebuilding a 148 gtl and have found caps that are leaky and dried out...after replacing nine the volume went up to a good level...now i need to fix the distortion
and background hash. Did you know that there are many posts
on FIXYA about this same problem I.E. great TX , great PA but poor , or no audio out. these sets have been made in sevetal countries...The sets made in Taiwan or China have poor quality
front panel pots (the carbon track is micro thin and simply wares through to the material the track is printed on) This has the same effect as removing a wire from a pot I.E. no audio. The good news is that 99% of parts in the radio are freely available and that includes the front panel controls. ONE WONDERS IF THE SET IS WORTH THE EFFORT !!!
CHEERS GUYS / GIRLS.
Posted on Jul 03, 2008
I just received a Cobra 2000 GTL from Ebay. When the radio is on there is a steady tone, similar to the sound of morse code is the speaker. The volume control has no effect on the tone. You can still hear other stations through the speaker, but the tone overwhelms it. I bought this radio used. It looks like someone tried to jump the PLL with the speaker switch, but they didn't change the PLL, it still has the MB8734. I removed the jumpers to the PLL.I plugged the speaker into all outlets, SP1, SP2, AUX, and even the headphone jack. Any help is appreciated. Thanks
Posted by propage1 on
am carrier 4.4 volts will not ajust...ssb carrier will 3.5 volt will ajust but max out put is only 3.5 volts.losses all voltage at ssd carrier when switched to usd r lsb
Posted on Feb 05, 2010
i need it for expanding the band
Posted by HARTA... on
Posted on Nov 09, 2011
Need to know how to install a varieble on a Cobra 1000 GTL.thx
Posted by www... on
This is a complicated modification. I have never done it to a 1000 GTL, but its done basically the same in all radio's.
I don't recommend doing it, especially since I am not 100% sure on how exactly to do it. I have never been in a 1000 gtl. If I had one in front of me I could tell you for sure how to do it.
If the reason for Variable power is a linear, just a swing kit in for the dead key you need, most likely 2 watts, and leave it.
Here is how to do a variable power mod. this is assuming the swing mod is done the same to this as a cobra 25/29 or uniden 68/76 etc.
If you would like to try it, here it is.
You get a TIP31 transistor, Radioshack has them.
Where you put the swing mod in the radio, which is a cap and a resistor, you put the TIP31 and cap. A 47uf cap works fine.
With the resistor facing you, and the tab in the back away, solder the cap to the transistor. the leg with the black stripe goes on the right most leg. then the other goes to the center leg of the transistor.
Solder a wire on the left most leg, long enough to reach the front of the radio. Now solder the 2 legs that don't have the wire on it, in the place where you would put the swing kit, with the black stripe on the cap facing the back of the radio usually.
Remove the wires from the RF gain and solder them together.
Now solder the wire from the transistor to the center tab.
Remove VR6 and solder a wire from the top tag of the RF gain to the top connection of VR6 that you removed.
Then connect a wire from the bottom tag to a ground point. The side of a tuning can works fine.
Take a piece of shrink tube and put it over the TIP31 so it does not ground against the heat sink, that would be bad.
This is done basically the same in all cb radio's.
Posted on May 03, 2009
i have a dynamike plus looking for battery 7volt can anyone help?
Posted by jcwilson3 on
At a pinch you can use 5 x LR44 button cells, yes that does add up to 7.5 volts but that's near enough, the 5 cells on top of each other are exactly the same size height and width as the 7 volt battery. I am using them in a "Telex" mike
Posted on Feb 18, 2010
I can not find the schematics for a cobra 148 NW ST. All I want to do is find the modulation and max it out for my neighbor.
Posted by callen7720... on
Most units do NOT allow modulation adjustment as any more than 90-100% modulation causes adjacent channel signal "Splatter" therefore is subject to restrictions, hence generally that is locked. Also there really is no reason to have more than 100% modulation..as well ... why? I would suggest a voice/speech "Compressor" would be more suited.
Posted on Feb 01, 2010
all voltages seem to be right but still will not show more than 1 watt
Posted by worldofcb on
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
Posted on Oct 17, 2009
How do you install a Astatic Echo Board in a Cobra 148?
Posted by ericmason1... on
There should have been instructions that came with your reverb board. You are going to need to drill another hole in the case of the radio, or find a control where you can install a dual control knob onto.
Your reverb board is likely going to need 8v, so you will need to locate that off the logic board, likely from the frequency synthesizer. The the audio lines from the mic, or the output of mic amp, are going to be redirected to the reverb, and the output of the reverb feed back to where the wires were removed from.
If I recall correctly, the 148 is a bit of a bear to work with, not much room inside. You will likely have to get creative in placement of the reverb board itself. Make sure to wrap well so that it doesn't get tossed around and break something inside.
Posted on Sep 15, 2009
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