| Author |
Message |
    
HELPME
| | Posted on Saturday, January 11, 2003 - 11:20 am: | 
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I HAVE A COBRA 2000 THAT EVERYONE SAYS I WARBLE OR SOUND WATERY ON SSB BUT ON AM THEY SAY I SOUND GOOD. ANY IDEAS OR LINKS FOR HELP? |
HELPME
| | Posted on Sunday, January 12, 2003 - 1:38 am: |
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Anyone??? |
Tech833
| | Posted on Sunday, January 12, 2003 - 12:32 pm: |
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Power supply capacitors are weak. |
HELPME
| | Posted on Sunday, January 12, 2003 - 12:53 pm: |
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where are those and what value? any infop would be great or even a repair web page link? |
HELPME
| | Posted on Sunday, January 12, 2003 - 12:56 pm: |
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Wait I hooked it up to a exterrnal power supply (MFJ 30 Amp) and it still does it????? |
2600
| | Posted on Sunday, January 12, 2003 - 9:43 pm: |
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If it is warbling on an external power supply, it's a little hard to blame this on the internal one. The internal power supply on the Cobra 2000 has several potential weak points. If you get it to sound clean on the external one, you may find that there are TWO problems, and the one you are having now (with the external in line) is only one of them.
The single most important thing to ask about this kind of problem is, "Did it always do this since you bought it, or did it used to behave itself?" If it has ALWAYS done this since you bought it, I would look for a modification that is NEARLY correct. If it USED TO behave and sound clean on SSB, that points to a breakdown of some kind.
Since the external power supply is more than large enough for the 2000GTL, the problem must be on the main radio circuit board somewhere. The most common one I have seen involves the way some folks "stretch" the coverage of the clarifier. There was a guy around here who installed a 12-volt zener diode in the radio, under a glob of black RTV sealer. He would then "goose" the internal power supply (by tacking a resistor onto it) to deliver enough to hold the zener up to 12 volts. The clarifier is supposed to run from a 8-Volt regulator chip. Feeding it from 12 volts gets you another few kHz 'up' from the center of the knob. Considering how far 'down' they will go, I see it as a waste of time.
The other most popular way to get "warble" on SSB is with an EXPO kit, or similar channel expansion that uses crystals to substitute for the 11.3258 MHz one that comes in the radio. The wires between the radio circuit board and the kit must be as short as possible. Making them too long, or getting them too close to other wires can cause your transmitter power to "feed back" into the sensitive crystal oscillator circuit, and push the frequency around. Your frequency is probably wobbling around on AM, too. It's just a whole lot harder to hear on AM than on SSB. A small amount of 'warble' won't be noticeable UNLESS someone keys on you. The steady "heterodyne" tone that comes from two carriers on the channel will have a normal, steady pitch UNTIL you modulate, and then you will hear the pitch of the tone warbling in step with the voice modulation. An AM receiver just doesn't care if your carrier frequency squirms around NEARLY as much as SSB does. Nobody will be able to tell, just by listening on AM. If they flip to USB or LSB receive while you are talking AM, I'll bet they can hear the "warble" in your carrier tone, as if someone were keying on you.
If you have a rotary switch with quartz crystals mounted on it sticking out the REAR panel of the radio, you will have to move it to the front, so the wires can be shortened. Mounting one of these on the rear panel just invites this kind of side effect. I warn folks who just WANT it put there to kiss off running SSB, 'cause it's gonna warble on them, like it or not.
73 |
Beatlejuice
| | Posted on Tuesday, February 18, 2003 - 4:29 am: |
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sounds like your sideband bais is out of adjustment i have a cobra 2000gtl need help emial me and ill send you specs |
Crafter
| | Posted on Tuesday, February 18, 2003 - 12:32 pm: |
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Sounds like bia voltage to me too, someone tuned it up and messed with the bia's. |
Dave_123
| | Posted on Wednesday, February 19, 2003 - 9:40 pm: |
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IMO Bias balance or botched mod. Cheers D |
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