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Cobra 148 Gtl

Discussion in 'General CB Services Discussion' started by nicky, Jun 13, 2018.

  1. nicky

    nicky New Member

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    I just recently bought a Cobra 148 GTL and there's a rotary knob on the right side of the radio and I have IMG_2121.jpg no idea what it's for.


     

  2. kaos513

    kaos513 Well-Known Member

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    Could be upper and or lower extra channels
     
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  3. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Lets' see...

    Open it up!
     
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  4. nicky

    nicky New Member

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    I did have it open and it's just a pot. I didn't look how it was wired.
     
  5. nomadradio

    nomadradio Analog Retentive

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    Sounds like a carrier-power control for AM transmit, probably.

    73
     
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  6. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Oh, ok - thought maybe you had a photo - wired the pot to the main board? Or left open and dangling like they removed a board? (I'm thinking ECHO but thats' me...)

    ECHO would also have a "click" - like power on/off and volume knob - so if it doesn't then it's certainly something else...

    Thank you!

    :+> Andy <+:
     
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  7. nicky

    nicky New Member

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    It does have an on/off click just like a volume control. I guess I'll find out when I get it powered up.
     
  8. nomadradio

    nomadradio Analog Retentive

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    And if someone borrowed a used control from a junk radio to install a carrier control, it might have a "click", but nothing connected to the two lugs on the rear where the switch is connected.

    73
     
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  9. kaos513

    kaos513 Well-Known Member

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    probably a variable power mod
     
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  10. nomadradio

    nomadradio Analog Retentive

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    Or variable talkback. If so, the control will have been roached out years ago and do nothing when you turn it.

    73
     
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  11. nicky

    nicky New Member

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    IMG_2126.jpg IMG_2126.jpg IMG_2127.jpg IMG_2128.jpg IMG_2130.jpg
     
  12. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    That's echo...

    The long IC in there, I believe, is the "Bucket Brigade" - lots of other support parts though to add to this mystery - so I guess it's not solved yet...

    Otherwise it looks pretty clean - I'd like to say you gotta keeper - but then ...

    Does it work?


    :+> Andy <+:
     
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  13. nicky

    nicky New Member

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    I have had it hooked to a power supply and it powers up and all channels and lights work but I don't have an antenna yet. I've been busy with a honey-do-list.
    I'm taking it to a guy I contacted in Warren Ohio that works on them to have it checked.I will tell the rest of the story when I pick it up.
    James
    I've got my fingers crossed that it's ok but time will tell.:rolleyes:
     
  14. nicky

    nicky New Member

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    What do you mean "BUCKET BRIGADE" ??? I'm not familiar with that.
     
  15. nomadradio

    nomadradio Analog Retentive

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    The technical term is "Charge Coupled Device", or "CCD".

    It behaves like a row of electron buckets,so to speak. It has a long string of capacitors, each with a pair of switch transistors. One feeding into it, the other one feeding out. Each pulse of a digital input, called the "clock" will cause each bucket to dump its stored voltage into the next one, and accept the voltage dumped into it from the previous one in line.

    To use it for a voice echo, you feed your audio into the first bucket via the analog input pin. The output from the last bucket gets fed back into the input pin. The audio is a string of analog "snapshot" samples of analog voltage you feed into it. The speed of the echo changes when you change the frequency of the clock pulses.

    The chip was developed as an image sensor. Each capacitor "bucket" would get charged in proportion to the intensity of light that falls on it. After you close the shutter, you pulse the clock input to get all those analog pixel voltages out of it.

    But if you put it inside an opaque black plastic package, nobody will know that it's light sensitive.

    73
     
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