Question about Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

No AM carrier or modulation. SSB transmits good

I am receiving and transmiting on SSB, but have no carrier signal or modulation on AM. What can I do? I have searched an repaired cold solder joints and checked final on side board near coax connector. It was ok.

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2 Answers

Great now check TR42 AM POWER then check TR41 AM POWER REG. They are on right side twards rear of board with front of radio faceing you part side up. A good place to start!

Posted on Jul 07, 2007

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  • 32 Answers

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

Posted on Jun 13, 2007

  • Alan washere Jun 13, 2007

    Sorry didnt see it was 148gtl. I dont have layout for that radio. But I know a sitehttp://www.radiomods.co.nz/membersareaco...
    this guy has alot of fault reports etc. He might be worth giving a shout.

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1 Answer

Yaesu 857D very poor audio out on SSB.


Dbl check your swr in am mode.. Ch your ssb power and mic gain default is 50 on both on hf .. If you use the mh-59 you will need to reduce the mic gain to 35 and it needs to be set for remote mic in the menu. Also the ssb needs to be set 2.5k wide with the ssb carrier zeroed both tx and rx

Apr 29, 2016 | Yaesu FT-857D transceiver

1 Answer

Transmits and receives no modulation out


I am not an expert but I think there can be little or no modulation of the carrier wave unless there is an audio input to the modulator. Like any audio amplifier a transmitter modulator (amplitude modulation) is quiescent without an input.

If the modulation amplifier and audio pre-amp are working and modulating the carrier wave and the antenna is ok then audio modulated radio frequency must be being transmitted.

It would be an extremely good quality CB that had a modulation meter. Mostly all they have is a meter giving an indication of the rf power being sent to the antenna and that rf (radio frequency) power would be the same whether modulated or unmodulated.
The modulation envelope, incidentally, is traditionally viewed or measured with an oscilloscope.

The indicated rf power could be verified using a field strength meter but the only practical way to discover if a standard CB is transmitting modulated rf is to listen to the transmission on a suitable receiver. If the squelch is turned down it will be obvious if the rf carrier wave is being received as the hiss would be silenced. If no audio is received it can be assumed none is being transmitted.

I suggest you try another microphone and lead and if that doesn't work it is clearly a job for a repair shop.

Oct 28, 2015 | Radio Communications

1 Answer

Why is there no transmit modulation?


'mic gain' adjusted for optimum amount of modulation?

Oct 15, 2015 | Radio Communications

1 Answer

Yaesu ft-990 no receive or transmit


Lynn, SSB (Single SideBand) only applies to AM (Amplitude Modulation) transmission. There is no way to broadcast SSB in FM (Frequency Modulation) mode.

May 16, 2015 | Yaesu Radio Communications

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...

2 Answers

My ranger 2950 will receive but will not transmit, also where can i get a 6 pin mike for this same radio ?


check tr 51 (Q 51) the sb754 on the back side mounting of the radio.. the center pin (collector) of this modulator ic should not be 13 volts. my bet is that it is.. this test is done in am mode.. not sideband.
depending on you carrier setiing it should be between 3 -8 volts any higher in am mode and my bet is that its bad... much more common than the finals in this radio. good luck Rick

Dec 13, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Sideband carrier??


im not sure carriers are measured in pounds, but SSB is a supressed carrier mode, in SSB only one sideband is transmitted and the carrier is inserted at the other end in the receiver. In AM mode the carried and both sidebands are transmitted. with regular am there is a carried and when modulation (your voice) is added a signal appears both above and below the carrier frequency at a distance relative to the frequency of your voice. so if you have a carrier at 1000 khz and modulated it with a tone of 100 hertz the signal will contain frequencies of 900,1000, and 1100 hertz, then its changed to SSB by supressing the carrier (1000) and one sideband (1100) if you are on lower sideband and (900) if you one upper sideband, and transmits the remaining frequency.

Nov 06, 2008 | Ranger RCI-2995DX Base Scanner

1 Answer

What is modem


Modem:

1) A device (modulator/demodulator) that allows computer information to be sent over a telephone line.

2) Equipment that converts digital signals into analog signals for purpose of transmission over a telephone line. Signal is then converted back to digital form so that it can be processed by a receiving computer. Modems are typically used to link computers via telephone lines. ...
3) Acronym for MODulator/DEModulator. A device that transforms digital signals from the computer into electrical impulses for transmission over telephone lines, and does the reverse in reception.
4) A modem (from modulate and demodulate) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. A device that transmits digital data in tones over a phone line.

IN GENERAL IT IS A DEVICE TO CONNECT THE COMPUTER TO THE INTERNET.

For more detailed info about the modem click here

Hope this helps

Sammy

Sep 04, 2008 | Computers & Internet

1 Answer

SSB radio


If you are using the radio on a boat, then no, the grounding does not matter that much. However, an SSB transceiver would be hassle to install on a boat because of the amount of power they use to transmit. If the transmission is bad, try using the radio's internal tuner instead of the separate tuner. This may help improve the quality of transmit, however, some radios have a tough time clarifying incoming and outgoing signals and create a garbled sound when it receives a signal or when it transmits. If that doesn't work, then you can try grounding. But if you want a radio that doesn't require all this nonsense tning, you might want to think about investing in a Yaesu. They are pricey, but are one of the best HAM radios.

Sep 04, 2008 | Ranger TR-696F SSB CB Radio

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