Question about Uniden Bearcat Pro PC68XL 40-Channels Base CB Radio

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No modulation key mike aND NO MODULATION

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I think you will find the Finals are blown in this radio.

usually caused by a bad antenna or a problem with the coaxial cable.

Posted on Jun 13, 2010

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1 Answer

Cb troubleshooting


Sounds Like a wire is broken on the mic connector. Disassemble the microphone plug and check the connections. Also There is a relay inside the 139XLR that is quite old by now and could possibly be worn out or dirty.

Jul 04, 2014 | Radio Communications

Tip

Problems in CB Radio Receive and Modulation


Much of the time complaints about CB receive (RX) and modulation are caused by problems in the antenna system. Make sure there are no shorted or open connections in the coaxial cable or PL-259 (screw-on connectors for coaxial cable, located at the antenna and rear of CB radio) connectors. Use your radio's meter or better still, a Power/SWR meter to check the SWR (Standing Wave Ratio) of the antenna. Try to get that as close as possible to a 1:1 ratio on the meter. A shorted or open antenna can keep the receive audio on your radio at very low levels. Plus, this will harm your transmitter if you continue keying the mike.

Another problem can surface in the radio itself. This will be noticed if you can transmit, but have no "modulation". Modulation can be described as the voice heard above the "carrier" (your transmitted signal). Every CBer knows about the term, modulation. The Truckers will definitely inform you about your modulation quality...lol. This problem can be caused by a defective AMC (Automatic Modulation Control) stage in the receiver circuit. Also, there will be no modulation upon transmit.

One other thing could be causing this lack of receive audio. Defective wiring or switching in the microphone can result in no audio. Additionally, in many radios, a missing mike will not allow receive, because the microphone connection completes the RX (Receive) circuit.

Solutions:
1. Check the antenna system, and fix any problems.
2. Check mike, or substitute another one.
3. Using meter, and/or another radio for listening on same channel, check power and receive.
4. You can probably fix 1, 2 and 3 yourself, or with the aid of a friend.
5. AMC problem in radio (as described above) will require professional service from a CB (Citizens Band) repair facility.

The above suggestions and advice will assist in repairing the majority of the symptoms described.

Regards, Bill

on Sep 18, 2010 | Car Audio & Video

1 Answer

No modulation on my T-240 Robyn's CB


bad mike maybe bad SWRs antennas not grounded

Oct 01, 2012 | Cars & Trucks

1 Answer

Have a sequel when keyed up


If this is a powered mike the modulation is set to high. If you have a standard mike check your settings on the radio, if that does not help sub another mike.

Apr 03, 2012 | Cobra 29 LTD CB Radio

1 Answer

How do I turn up key and adjust modulation on cobra85 dynascan base CB?


The best way to solve this problem is to find a power mike for the radio, it will bring the modulation up to 100% instead of the 25-30% that you are currently working with and your carrier wave will have a lot more punch. Ham radio shows are worth checking to find what is needed, or second hand store may be another option.

Feb 29, 2012 | Audio Players & Recorders

1 Answer

Will not get good recepiton.


Hi stormnorm157,

Much of the time this is caused by problems in the antenna system. Make sure there are no shorted or open connections in the coax or PL-259 connectors. Use your radio's meter or better still, a Power/SWR meter to check the SWR of the antenna. Try to get that as close as possible to a 1:1 ratio on the meter. A shorted or open antenna can keep the audio receive on your radio at very low levels. Plus, this will harm your transmitter if you continue keying the mike.

Another problem can be in the radio itself. This will be noticed if you can transmit, but have no "Modulation". Modulation can be described as the voice heard above the "Carrier" (your transmitted signal). Every CBer knows about the term, Modulation. The Truckers will definitely inform you about your modulation quality...lol. This problem can be due to a defective AMC (Automatic Modulation Control) stage in the receiver circuit. And, there will be no modulation upon transmit.

One other thing could be causing this lack of receive. Defective wiring or switching in the microphone can result in no audio. Or, in many radios, a missing mike will not allow receive, because the mike connection completes the RX (Receive) circuit.

Solutions:
1. Check the antenna system, and rule that out or fix.
2. Check mike, or substitute another one.
3. Using meter, and or another radio for listening on same channel, check power and receive.
4. You can probably fix 1 and 2 yourself, or with a friend.
5. AMC problem in radio (as described above) will require professional service.

Let me know how this turns out, and inform me if I can offer any more help. Thanks.

Regards, Bill

Sep 18, 2010 | Midland 1001Z 40-Channels Base CB Radio

1 Answer

COBRA 21 GTL NO MODULATION NO RX. BUT IT WILL TX AT 3 WHATTS.I HAVE TRIED 3 DIFFERENT.MIC ON THIS RADIO CAN YOU HELP ME


That's usually a defective amc stage that produces RX audio and TX modulation. It's an integrated circuit that will require a tech fixing it. You will have a transmitted carrier with no modulation, and no sound in your speaker. However, make sure you have a good mike plugged in first, and substitute a known good mike to verify it's not the mike.

Jul 30, 2010 | Radio Communications

1 Answer

Key mike no hears me but shows meter


You didn't mention if you hear the other radio. If not, here's a common problem and solution.
That's usually a defective amc stage that produces RX audio and TX modulation. It's an integrated circuit that will require a tech fixing it. You will have a transmitted carrier with no modulation, and no sound in your speaker. However, make sure you have a good mike plugged in first, and substitute a known good mike to verify it's not the mike.
However, if you hear them, and they see your signal, but no talk (modulation), then the problem is usually your mike. Try another one in this case. Thanks, Bill

Jul 27, 2010 | Cobra 19 Ultra II CB Radio

1 Answer

Cobra ltd classic no modulation


Assuming that you've tried another mike, the problem may lie in the speech amplifier circuit within the radio, something that will require someone with technical knowledge to repair.

Sep 22, 2008 | Cobra 25 LTD 40-Channels Base CB Radio

3 Answers

Mod


You never want to clip modulation limiters All youll get is a overmodulated splatterbox and it will sound like crap!! Try cbtricks.com and youll find the tuning info for that radio...Chia

Dec 24, 2007 | Cobra 150 GTL DX Base CB Radio

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