The NRL switch has broken a contact or is simply not making contact...check the wireing going to the switch at the switch and
and the board end. These switches often play up and are freely available from electronic parts store
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Are you following the user manual that came with the radio?
NB-ANL/CB/PA SWITCH: When the switch is in the NB/ANL position, the Noise Blanker (NB) and Automatic Noise Limiter (ANL) circuits are activated.
The Noise Blanker is very effective in eliminating repetitive impulse noise such as ignition interference. In the CB position, the PA function is disabled and the radio will transmit and receive on the speaker that is connected. In the PA position,
the radio acts as public address amplifier. Your voice will come out of the speaker that is plugged into the PA. SP. jack on the rear panel. The radio does not operate when you are in the PA mode.
When you plug a speaker into the ext. jack does it kill the radios internal speaker? It should until you unplug it; if not and you are following the about you may have a wiring issue with the jacks.
OK bare with me now i have no idea of your knowledge level with CB/ SSB radios.
Lets make sure our setting on radio face is correct before we decide this is an mechanical problem.
Set the following
Volume knob 12 o'clock
Dynamike knob 12 o'clock
Squelch full counter clockwise
Rf gain full clockwise
Select S/RF position on the SWR/CAL switch
Select AM position on the USB/AM/LSB switch
Select CB on the CB/PA switch
Now there will be some critics with opinions on the next instructions. Place a small screwdriver or test lead from a multimeter in center conductor of antenna jack listen for onair noise or radios operators to verify RX is working. Now remove the antenna/screwdrive/testlead. Then key mic just long enough to notice if the meter is swinging do not hold the mic button long this can damage the final. I tell you to do it this way rather that connected to your antenna system so we can eliminate the question if it is you antenna sytem or the radio.
If the LSB or USB was selected when you keyed the mic you would see no meter movement this is due to the lack of a deadkey or carrier for SSB which is a much more efficient method of transmitting on AM.
There are few things that affected the rx and tx together.
Volume/Squelch control: As desired
ETone: Sets the sound of the echo as desired
MicGain/RF Gain control: Normally, leave fully clockwise
Band Switch: for CB, turn all way to left (a/e)
Mode Switch: Selects how you modulate the radio. Normally, you will operate on AM, USB or LSB.
Fine/Coarse control: Changes the frequency you operate on. Normally, set so the frequency counter reading ends in 5. (center slot of the channel).
RB: Roger beep. Turn on or off as desired.
NB/ANL: Noise limiters. Leave on.
Frequency Counter: Turns counter lights on and off.
+10 KHZ: Allows you to get the channels missed by the Channel knob. Normally, leave off.
Power: Selects either high or low transmitter power setting.
Band: Selects band of operation. Low (A-D) or High (E-F)
What you are getting is ignition noise from the engine of your car. Could be spark plug noise or alternator whine. If your radio has a ANL or NB switch, turn it on. If that does not fix it, you may have to get a filter for your powerline or change where you are getting power for the radio. Hope this helps, with the limited info available. Let me know,,,Mechanic
Do you remember the old 40 channel CBs? they used basic A3A transmission (dual sideband single carrier)remember how you got crosstalk sometimes, if your power was too high? Then they went to 80 channel CBs (using a single side band as Lower Side Band (lsb) and the other as the upper side band (usb))? more crosstalk but they invented anl (automatic noise limiter)circuitry to compensate. Now you have the 120 channel CB which uses a form of side band multiplexing (20QAM) to generate 3 times more channel density 40 X 3 = 120. Here is my problem; Cobra should not have done this because you will have massive crosstalk and unaudible sounds because of the increase in channels but not an increase in initial (physical)bandwidth. I hate to tell you this but the only cure for the is to use it in 40 channel or 80 channel mode forget the 120 channel mode, or get a radio with better channel separation.