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View Full Version : 1. 148GTL SSB Transmit and Receive (Moved From Mobile-Radios w/ Added Finds)



Redbeard
08-18-2018, 11:41 PM
148GTL is acting strange on trans. and rec. boughtit from shop year ago and just now hooked it up. Charlie's Airwaves in Houstonhad it on a shelf. Clarifier is unlocked (slides 16 KHz, about 8 KHz bothways). Testing it I was told I sounded off freq., had to adjust clarifier ontrans. On receive I have to adjust clarifier to keep from hearing the spacealiens on helium. Knob setting forrec. is about 11 o'clock. Knob setting for trans. is almost 1 o'clock. Myco-conspirator in test was only a few miles away. Knob Jockeying is not my ideaof fun to communicate. Anyone have an idea what can be done to remedy this 148ailment?

Never mindthat.....this thing has been modified by a golden screwdriver. Has some kind ofchannel mod installed. NB/ANL, HI/LOW, and BRT/DIM change frequencies. Thedifferent positions seem to only change the freq from what is shown on LEDdisplay. NB/ANL-LOW-BRT changes Chl. 29 to 27.935(10M). NB/ANL-HI-DIM changeschl. 23 to 26.935(LSB 38). Some positions duplicate freq. This thing is F'd up.Screws holding board down are all soldiered. The Ext. speaker and PA have beenjumped over to create Talk Back. Guess I'll build a Road Map from Hell for allchl. configurations. Thinking this may be some form of Enigma Machine. Threeswitches change chl. freq's- the Enigma had three wheels in it that changed keyoutput. Any help would be greatly appreciated.
Found this online at Anglefire:

1. Replace 11.1125 crystal with an 11.3258 crystal.
2. Isolate the ground pin 10 of the MB8719 PLL by cutting the PC trace.
3. At this point, turn your radio on and check to verify that all channelsarelocked in and working. If it is not, adjust these in the following order:
a. CT3 for USB.
b. L20 for LSB.
c. L19 for AM.
4. Install a SPST switch between pins 11 and 12 of the MB8719 PLL
5. Install a SPST switch across the cut you made to isolate pin 10.
CHANNELS:
SW1 / SW2 DOWN (NB/ANL-LOW-DIM):NORMAL 1-40
SW1 UP / SW2 DOWN (NB/ANL-HI-DIM): (ch.15-27) 26.815 to 26.955
SW1 UP / SW2 UP (ANL-HI-BRT):
1= 27.605 6= 27.505 11= 27.565 20= 27.525
2= 27.455 7= 27.515 12= 27.585 23= 27.575
3= 27.465 8= 27.535 13= 27.595
4= 27.485 9= 27.545 14= 27.605
5= 27.495 10= 27.555 16= 27.475
SW1 DOWN / SW2 UP (NB/ANL-LOW-BRT): (Ch. 1-40) 27.605 to 28.045

Anyone with any advice is appreciated.

mattsowders1989
08-19-2018, 12:31 AM
My advice is to take it to a tech. A good one


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Redbeard
08-19-2018, 05:00 AM
None to be found around Port Lavaca, TX. Couple I wouldn't trust in Houston (3 hrs. away). Nothing in Corpus. Clay's CB in San Antonio is about the only reputable around these parts. Used to know one in Mobile 20 years ago. I'm sure he's dead by now. There used to be one around Walker, LA. He's dead for sure. This radio is driving me nuts. Got any suggestions?

222DBFL
08-19-2018, 05:14 PM
Depending on how much it is to fix, the uniden 980 might be a bit better choice. It may not have the name or clout the old cobra 148ís had but they are great little SSB radios that come dead on frequency out of the box. I know mine was and have heard a few others say the same. Last I saw they were not too expensive, at $95-$120. Good price for a new SSB radio. Just some food for thought sir. Good day

mattsowders1989
08-20-2018, 01:23 PM
Well you could always mail it to a tech. Lot of people do that with Nomad Radio here in KY. Or if you want to try to line it out yourself, Iíd start with buying a freq. counter somewhere and google alignment instructions for the radio and realign it.


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mattsowders1989
08-20-2018, 01:25 PM
The only thing I hate about the 980 is the SMD in it. I had a hard time trying to get a variable carrier control in it. I donít want to throw a huge carrier out there in a linear.


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Redbeard
08-20-2018, 02:53 PM
Have the freq. counter, have the alignment information. Inspected internals. Noted the mods. Buying all the Cracker Jack's I can in hopes to find that "Secrete Decoder Ring" for the chl. mod. Had friend with more knowledge come over and inspect it. Figuring Charlie has it wound too tight. Heating a cap or two. 4 W dead key, no swing. We decided it would be best to take it back to Mr. Charlie to have him look at it before we tried anything. Always willing to give an honest man an opportunity to correct a mistake. Heck I bought it and didn't mess with it for 7 months until I built and erected antenna and break over. If he is willing to try to work on it to correct problems without charging me, then that tells me about character.

The 980 is a stable radio, friend of mine is drooling over one right now. He found one up in Hill Country last week. Believe it or not there is a Radio Shack left. They wanted $160 +. Too much. Looking around found them for $117.

I hear good things about 980, but I like the old school radios. Have my Stryker SR-497HPC. Coupled with Palomar LD 450, I can melt my antenna, if I hadn't had to take it down.....again. High winds were working voodoo rituals on the base, I'm lucky it didn't fall down.

Redbeard
08-21-2018, 04:49 AM
Think I may have found something, dumb luck. On another site found a post about "MOSFET's and the 148GTL". On page 3 was this interesting info:

A little info on removing TR24 in this chassis.DONT DO IT!

"Removing TR24 upsets the ALC and causes SSB distortion.
pioneer, I’m wondering if some of the distortion issues you had on SSB whenworking with your MOSFET mod might have been due to TR24 being gone.

To remove the AMC limiter in AM mode only, the transistor to remove is TR26.
I just remove R131 instead, and if you look at the schematic, you'll see it’sbasically the same thing."

Page 4 found this:
"The 148 effectively has two modulation limiters. One for AMcalled the AMC (automatic modulation control) and one for SSB called ALC(automatic level control). Each is controlled by one transistor on the board.There are many ways to disable the circuit from removing the individualtransistor to removing a resistor. The end result is the same.

I don't recommend disabling the SSB ALC circuit as this can cause moredistortion problems then disabling the AM AMC. The things to remember here areto keep your mic gain at the right setting. If you disable the AM limiter andkeep the mic gain under control, you will have a more natural sounding audioquality with higher modulation peaks.

Adjusting the AMC variable potentiometer for the maximum modulation setting isnot the same as disabling the circuit. Even at maximum modulation setting ofthe VR the limiter is still clamping the audio peaks. This may not be a badthing if you don't have access to a scope to find the setting that providesmaximum modulation without flat topping on positive peaks or worse yet, cuttingoff the carrier on negative peaks. This is the number 1 cause of adjacentchannel interference on CB."

Had to open mine back up. Sure enough TR24 was AWOL. Sitting adjacent to the vacant spot for TR24 the C208 was corroded/ eroded. We had guessed on a cap or two being bad. R131 had been clipped and cold soldiered back for some reason. It was standing straight up and down, not sure if that is factory or not. Service manual picture is not clear on that.

Now! If I just knew what the hell I was talking about.