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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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

How do i know if my palomar 250 is a high drive or low drive amp


If it is made by Palomar and it is a small amplifier, you can bet it is a low drive. Check those transistors. It could have the new Mosfet 655's in which case definitely low drive 3-6 watts input max.

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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.

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Have a Magnum 257HP 10 meter radio. While connected to a 50 ohm dummy load, and a power meter, noticed that the USB and LSB would not modulate when a voice input is placed into the microphone. Also, on...


You may have a radio where the AM limiter has been defeated which can cause all kinds of issues. I would first check the mic is wired right and does not have a problem, the radio should have output with a tone to it on sideband--wattage up to over 20 watts on SSB is normal.

Dec 12, 2012 | Magnum Radio Communications

1 Answer

Galaxy saturn tubro 100 watt power is sticking after key up.


Not sure what you mean completely. If you mean, when you key up, it keys at 100 watts and stays, then this is probably not a problem.

If it doesn't swing, it is either the watt meter you are using, or you have the power up too high, or both.

I usually key my saturn turbo around 80 watts. You have to be careful with these radios. they get hot fast and when they do, they get whacky. Make sure you have a PC fan plowing on the heat sink on the back.

The higher the dead key, the less swing you will see.

Now as for the watt meter....

There are a few types of meters out there. The 2 most common are ones that read AVG, or average watts, or PEP or Peak envelope power, which in short terms is your Peak wattage. Some meters do both.

An AVG meter will not read peak wattage, or swing. So if you meter is an AVG meter, or is set to AVG, then it will not read swing, and will show you your dead key, and that's it. Some times the needle will move a little, but it is not showing your true swing.

All in all a PEP meter is a loose representation any way, because you really cannot get an accurate reading when there is modulation. But it's close enough. You would need a spectrum analyzer to really see what you are putting out with modulation. AVG with no modulation is a more accurate reading however you cannot see swing.

Now PEP while transmitting in SSB with modulation, would be accurate. Just not AM, but like I said, its close enough and is what every one goes by.

I don't know if your Saturn turbo has been modded or peaked and tuned but, you should see a max of about 170 to 200 watts swing on that radio if its been done right. But you will need a PEP reading meter to see that.

I wouldn't run it past 80 watt dead key for long. With that radio you should really only run what you need. For instance, when I am using mine, I start at around 70--80 watts, and do a check, and if it's not strong enough I bring it up a little, until the audio sounds good to who I am talking too.

Like I said, you have to keep it from getting too hot.

Nov 04, 2010 | Radio Communications

2 Answers

I have a 77 that has got hardly any swing anymore.it keys 3-4 watts and won't swing past about 8 watts.i used to get 25 watts plus swing out of it. i have replaced the finals and it did not help.any ideas?


Is this just on the AM side or also on SSB?
If you type in 77HML or Galaxy 77HML in your Search Block,you should have a listing for cbtricks.com. and it should say Manual.This will give you Schematics,Transistor Voltages,Parts Placement and Specifications anything you would need is on this page.There are 3 Transistors on the Back Right Corner of the Radio looking at the part side,TR-49 is a predriver for TR-50 and TR-51,which are your AM Modulation Transistors.Hope this helps you out.

Jan 24, 2010 | Galaxy Radios DX 77HML Base 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

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

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

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