Question about Uniden PC78ELITE 40-Channels Base CB Radio

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No Modulation!! Have an old uniden 40 channel am/ssb tranceiver,can't find model number,have sn; 43001163.Seems to be transmitting,but no modulation

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  • Rudd Feb 09, 2008

    Since my original Post,I've found the cb to be a Uniden Madison 40 ch am/ssb,would your solution still apply? Also does the mic cartridge ever/often go bad?

    Thanks in Advance Rudd

  • Rudd Feb 09, 2008

    Thanks Again!! Probably be talking again after further investigation. Later

  • Raul Garza May 01, 2013

    I am having same problem,I do receive but do not get out,(modulate) meter does not register either.

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  • Master
  • 6,966 Answers

Hi,

Most modulation problem could be traced to:
1. mic or the cable and/or the mic connector;
2. AMC (amplitude modulation control) - it's a single transistor that regulates modulation and occasionally has been known to clamped on the mic audio;
3. the AM/SSB switch - spraying with contact cleaner is a temporary remedy; and/or
4. audio amp - however if your receive audio is good, then this does not apply.

Hope this be of initial help/idea. Without a model number, I can't be more specific as to component(s) or PCB location but pls post back for any developments (or lack thereof) or should you need additional information.

Good luck and kindest regards.

Posted on Feb 09, 2008

  • Louie  Role
    Louie Role Feb 09, 2008

    Hi again,

    Your particular model shares the basic electronic design with some Cobra models (+/- some features). And yes the initial post would still hold true.

    Re the mic - most prone to defect is the end of the cord towards the connector where it is constantly flexed. Normally the white wire is the mic audio line and gets cut somehow. You would need the use of a DVM or a continuity tester and a soldering iron if this is determined to be the issue.


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1 Answer

Why no modulation in transmit mode?


Without seeing it I would guess (and it's only a guess) that maybe you have a broken microphone wire. If it's a factory mic the most common place for it to break is right up from the mic plug. Factory cords are not flexible, their really stiff. We could really use some more information. Mike

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'mic gain' adjusted for optimum amount of modulation?

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check to see if the radio had the diode clipped . If so then replace it to see if thats the problem.

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Adjust modulation pot cb


4 watts on am and 12 on ssb the modulation pot isn't going to help you . go to www.cbtricks.com and get the service manual.

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1 Answer

Please explain a 10 meter am/fm radio


Okay.

You do set this up like a regular CB. The meters refers to how long the waves are. CB is 11 meters. So its very close. The antenna woud be tuneds slightly shorter. Use the SWR meter in the radio to calibrate just like you would a normal cb.

Now for the ABCDEF knob. each letter is 40 channels in the band. So A would be 1 - 40 channels, then B would be the next 1 - 40 channel frequencies. You use the frequency counter in the radio(providing that model has one) to tell what channel you are on.

Here is some info one the frequencies in the band.

Now for AM and FM. this is the type of modulation you are using for transmit and receive.

CB transmits on AM or SSB. Amplitude modulation or Single side band. Most CB radios only have AM. But some also have SSB. None will have FM.

FM is frequency modulation.

10 meter radios can have AM FM SSB and DSB depending on the model and options it comes with.

So your radio has 6 ranges for freqency. each is 40 or 50 channesl. Not sure what model you have. If it has 40 then you have 240 channel freqencies.

with AM and FM, you double that, because you can talk on AM or FM on all the channels. If you are on AM and some one transmits on FM unless they are really close, you will not hear them at all, but if you do with will just be garbbled noise.

Also Am and FM both work a little different with range etc.

Now, you may be able to talk on the CB channels as well. Cb starts at 26.965 MHz and ends at 27.405 MHz. The channels are all .010 MHz appart.

Hope this helps

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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.

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2 Answers

Just want to know if i should use my ll203 amp in am or ssb mode when running with a cobra CB radio?


What radio?? Does it have single side band(SSB)? If not, then don't use SSB.

AM - amplitude modulation
SSB - single side band.

If you have SSB, there would be a switch on it to transmit in SSB. If not, it is AM only.

Second, Has this radio been worked on to be able to run on an amp? If not, you will blow the amp.

A CB radio transmits dead keys with 4 watts of power, and transmits with 4 watts of audio.

a 4 watt dead key is too much for a linear amp. You will smoke the transistors. Also, 4 watts of audio is not enough to drive it properly. You won't get full power.

The dead key needs to be around 2 to 2 -1/2 watts,or what ever makes the linear dead key half its peak wattage., and the modulation (audio) turned up all the way.

It doesn't sound like you know too much about CB radio's. Not a big deal, you can learn. For right now you may want to take it to a cb shop and tell them you want a peak and tune, and set up to run a linear.

You can find CB shops usually at truck stops. Some area's they are other places. Check the internet for local shops.

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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

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