Question about Cobra 148 GTL 120-Channels Base CB Radio

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142 GTL Good AM Carrier Weak Modulation????

Weak AM modulation at 50% on Palomar PW-5000 meter. SSB has low forward swing with low modulation?? I have checked many voltages in the past and all that I have checked seems normal. Using SAM's Photofact. Re-align transmitter as per Sams with 2-tone audio generator and still low modulation. Replaced Audio IC TA 7222P no change. Any Ideas???

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  • Mike Autry Mar 24, 2007

    UPDATE:
    IC4 TA 7222P Voltage Check:
    PIN1 = 13.76v RX / TX = 13.66v
    PIN2 = 7.04v RX / TX = 7.00v SHOULD BE 2.95v !! ??
    PIN3 = 0v
    PIN4 = 0v RX / TX = 0v
    PIN5 = 1.162v RX / TX = 1.162v SHOULD BE 1.95v ??
    PIN6 = 1.158v RX / TX = .8v (Gradual drop in voltage during TX Mic Gain @ Min. like capacitor unloading) SHOULD BE 1.95v
    PIN7&8 = GND
    PIN9 = 7.27v RX / 7.18v TX
    PIN10 = 13.10v RX / 13.00v TX

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2 Answers

Have you checked TR 26 AMC amp, and TR 24 & 25 AMC amps also for SSB TR34 ALC amp. make sure all voltages are right if all checks out try lifting out of the board or cut the collector of TR24 and try it. oop's that slipped out.

Posted on Jul 07, 2007

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You may have to scope the finals circuit on the modulation to see if all the "inline" caps are installed correctly... be sure your pc board is grounded in all areas as required by specs in your manual. Make sure there is no bleedover and you are sheilding your crystals from the modulation platform. al

Posted on Apr 30, 2007

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1 Answer

What is Dead Key on a CB Radio?


Deadkey is slang it is CW or Carrier wave which is RF power produced before modulation/audio is mixed in which stimulates PEP wattage slang being SWING WATTS. A Watt Meter is used to measure it which is often a combination device Wattage/SWR/Modulation meter.

May 08, 2013 | Galaxy Radios DX-949 CB Mob ssb Swr...

1 Answer

I have a Realistic TRC-457.It has very low power and modulation.It is a virgin radio other than someone has replaced the final and driver.I noticet that I cant set the modulation and swr levels on my dosy...


How many watts does it do? If it swings say: 1.5 watts up to 4 watts, someone has installed a swing kit which has a very small carrier. In AM, carrier is not important, its modulation and swing that makes it loud. If its low Audio modulation then it may be that final has went bad too.

May 31, 2011 | Radio Shack TRC-503 CB Radio

2 Answers

How to adjust frequency on transmit??? Galaxy


hELLO THERE
hERE IS SOME MODIFICATIONS FOR THIS RADIO
Galaxy Mods DX 2527 - VR 1....AM/FM S-Meter, VR 2....SSB S-Meter, VR 3....SSB Squelch Range, VR 4....AM/FM Squelch Range, VR 7....SSB Carrier Balance, VR 8....RF Meter, VR11...Driver Bias, VR12...SSB ALC, VR13...Hi Power, VR14...AMC, VR15...AM Low Power, VR16...SSB Low Power, VC 1....10.240, VC 2....10.240. DX 2517- VR 1....AM/FM S-Meter, VR 2....SSB S-Meter, VR 3....SSB Squelch Range, VR 4....AM/FM Squelch Range, VR 5....FM Deviation, VR 6....SSB Carrier Balance, VR 7....TX Offset, VR 8....CW Beep Level, VR 9....RF Meter, VR10...Final Bias, VR11...Final Bias, VR12...Driver Bias, VR13...SSB ALC, VR14...AM/FM High Power, VR15...AM Modulation Meter, VR16...AM Modulation, VR17...SSB Power, VR18...AM/FM Low Power, VR601..13.8 Volt Power Supply. DX 22B- VR 1....AM/FM S-Meter, VR 2....SSB S-Meter, VR 3....SSB Squelch Range, VR 4....AM/FM Squelch Range, VR 7....SSB Carrier Balance, VR 8....RF Meter, VR11...Driver Bias, VR12...SSB ALC, VR13...High Power, VR14...AMC, VR15...AM Low Power, VR16...SSB Low Power, VR21...TX Offset, VC 1....10.240, VC 2....10.240. DX 11B- VR 1....AM/FM S-Meter, VR 2....SSB/CW S-Meter, VR 3....SSB Squelch Range, VR 4....AM/FM Squelch Range, VR 5.....FM Deviation, VR 7....SSB Carrier Balance, VR 8....RF Meter, VR10...Final Bias, VR11...Driver Bias, VR12...SSB ALC, VR13...AM/FM High Power, VR14...AM Modulation, VR16...CW Tone Level, VR20...Final Bias, VR21...TX Offset, VR601..13.8 Volt Power Supply, VR803..AM/FM Low Power. DX 77HML, DX 88HL, and DX 99V- VR 1....AM/FM S-Meter, VR 2....SSB S-Meter, VR 3....SSB Squelch Range, VR 4....AM/FM Squelch Range, VR 5.....FM Deviation, VR 7....SSB Carrier Balance, VR 8....RF Meter, VR10...Final Bias, VR11...Driver Bias, VR12...SSB ALC, VR13...AM/FM High Power, VR14...AM Modulation, VR16...AM/FM Low Power, VR20...Final Bias, VR21...TX Offset.
Unmarked VR in R189..AM/FM Medium Power for DX 77HML only. DX 33HML, DX 44V, DX 55V, DX 66V, and DX 73V- VR 1....AM/FM S-Meter, VR 4....AM/FM Squelch Range, VR 5.....FM Deviation, VR 8....RF Meter, VR12...Low Power AM Modulation, VR13...AM/FM High Power, VR14...High Power AM Modulation, VR16...AM/FM Low Power.
Unmarked VR in R188..AM/FM Medium Power (DX 33HML only)
Unmarked VR in C139..Med Power AM modulation (DX 33HML only) DX 949,DX 959- VR 1....AM S-Meter, VR 2....SSB S-Meter, VR 3....SSB Squelch Range, VR 4....AM Squelch Range, VR 6.....SSB Carrier Balance, VR 7....TX Offset, VR 9....RF Meter, VR10...Final Bias, VR12...Driver Bias, VR13...SSB ALC, VR14...AM High Power, VR15...AM Modulation Meter, VR16...AM Modulation, VR17...SSB Power, VR18...AM Low Power, VC1....10.240. DX 2517 and DX 2527-
Symptom:Buzzing or motorboating sound in either the transmit or receive.
Problem: TR602 is oscillating
Cure: Replace C602 with a .01uF cap {Cap is located in the power supply board}.
RG 66,99,DX2517 Replace Q54 2SB754 60watt 7A with a higher power 2SB817 100 Watt 12A. Derating of this component will cool operation, provide better voltage stability,decrease wobble, allow voltage increase to 14.5 volts comfortably. (replace 10 volt caps in this section of the radio to a minimum of 16 volts before increasing supply voltage to this level)and provide faster swing rise time, Replace Q37 2SA473 to a 2SA1012-0 or ECG153 this will improve the clarity and volume of the modulation and it will also run a lot cooler.

Nov 12, 2009 | Galaxy Radios DX-949 40-Channels Base CB...

1 Answer

I have an HR 2510 that shows no dead key watts on AM ????


This sounds exactly backwards, you should have a carrier on AM with some forward swing, on SSB (sideband) there should be no carrier & all modulation (forward swing). Could you have the settings mixed up or has somebody put a modulation kit in your radio & messed something up or maybe one of the knobs has been removed & not replaced correctly ? Just a couple of things you might look into.

Jun 19, 2009 | Superstar Radio Communications

1 Answer

Tunring up a cobra 150 gtl/dx


Um... What?? This is hooked to a switch? CB radio by FCC regulations is only supposed to have a max of 4 watts total output. If you can flip it to 7 watts dead key, you are doing really good. It won't do much more then that. It sounds like its set up to run on a linear amplifier, which cannot have more then 3 watts dead key transmitting into it.

Dead key, and modulation are different. You may have a meter that only reads dead key, and won't see the modulation. This radio is probably swinging close to 15-20 watts. you need a meter that can read PEP, Peak envelope power. Cheap meters only read AVG, or average power, witch will only show your dead key.

7 watts dead key is really good for that radio.especially since stock only has 4 watts. you cannot get any higher then that without changing finals.

at 3 watt dead key, or 7 watt dead key, your modulation wattage is still swinging much higher.

Also, you will get more swing with a lower dead key any way, which is better if you want it to be loud.

Leave it alone. its probably set just right.

May 12, 2009 | Cobra 150 GTL DX 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

1 Answer

Cobra 148 gtl b no recieve


make sure that the rf gain is turned up all the way.Check diodes D-12&D-13.

Jan 08, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

148gtl, Taiwan when you modulate the meter swings backwards


In the back is where power mods have been added...It sounds like a swing kit 1/2 watt deadkey to 25 watts which is a powerful modulation exceeding 100%. Its a 220uf capacitor in place of a jumper J1 or J(x) J something in some radios. if you replace the jumper and remove the capacitor 220uf or 470uf one.(near finals it will return to around 4 watt dead key) The result of 4 watts is modulation is flat;where if you adjust it to 2 1/4 watt to say 20 watts it will be very loud and modulation is at 100%.

Dec 07, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Audio limiter


tintlady, here is the info you requested;
the AM limiter is R 276

These are the variable adjustments inside,and what they control.
VR-1 AM S-METER
VR-2 SSB S-METER
VR-3 SSB SQUELCH RANGE
VR-4 AM SQUELCH RANGE
VR-6 SSB CARRIER BALANCE
VR-7 TX OFFSET
VR-9 RF METER
VR-10 FINAL BIAS
VR-12 DRIVER BIAS
VR-13 SSB ALC
VR-14 AM HIGH POWER
VR-15 AM MODULATION METER
VR-16 AM MODULATION
VR-17 SSB POWER
VR-18 AM LOW POWER
VC1-10.240 MHz Frequency adjustment

Hope this helps you out, let me know,,Mechanic

Jan 20, 2008 | Radio Communications

2 Answers

No AM carrier or modulation. SSB transmits good


what cb is it ? it sounds like your am section is not getting powered up when you switch from ssb to am. If i know the model i may have a diagram of it here and suggest a place to start

May 02, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

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