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question on choke for slide

Discussion in 'CB Radio Modifications' started by sonoma, Apr 27, 2018.

  1. sonoma

    sonoma Sr. Member

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    I just got a B expo kit for a cobra 142gtl. it calls for a choke to help the slide. the instructions says to install a choke that was provided with the kit but it is not in the box. it says if you want more slide to use a 10uh choke. by chance does any one know what uh the original is or which way would I need to go to try to get the proper choke? I do not like a lot of slide since it is prone to make a radio drift. would I need to go to a 5uh or a 15uh choke to get about where the stock choke would be. if no one knows what originally came in the kit?
    I have a few conformal chokes, will that work in the place of what came with it, not sure if it was a wire wound choke or not.


     

  2. Robb

    Robb Yup

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    Try the 5uh. if it needs more, then toss in a 10uh.

    Didn't Lester's custom radios one of the last guy to sell those kits IIRC? Bet he has that info. Try emailing him?
     
  3. nomadradio

    nomadradio Analog Retentive

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    The choke that comes with the kit should be 5.6 uH.

    It does extend the clarifier coverage.

    But only if you install it correctly. Putting it in series with the clarifier circuit's varactor diode won't work in this model, or the other 8719 radios that have a trimmer cap for USB, and trimmer coils for AM and LSB.

    The setup that puts it in series with one leg of the varactor only works for the 8719 radios that have three coils, one each to trim USB, LSB and AM. The radios with the trimmer cap for USB are different. You have to put the choke in series with the crystal, and *NOT* in series with the varactor diode. This will require a cut in a pcb trace on one leg of the crystal, with the choke soldered across the cut.

    It also moves down the center of the channel on the clarifier.

    Good chance the radio won't adjust on channel with the clarifier at 12 o'clock with the choke installed. Trimmer won't go high enough.

    The typical cheat is to turn the clarifier full clockwise, and set the USB trimmer for 1.5 kHz above the channel center. The trimmer cap will usually be at the end of its travel to do this.

    Next, you turn the clarifier down to the channel center frequency, still in USB mode.

    Now, pull the knob off the knurl shaft of the control, turn the pointer to 12 o'clock and push it back onto the shaft.

    Next, set LSB and AM both for channel center without moving the clarifier. This will give you the same leeway above the channel center frequency that you had before. The remaining travel on the knob as you turn it to the left should get you about one channel down.

    About. Your mileage may vary. Might only go down 9 kHz. The radios that have three coils for this and no trimmer cap tend to travel farther down in frequency than this type PLL.

    73
     
    Robb likes this.
  4. sonoma

    sonoma Sr. Member

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    thanks Nomad. I have never used the B kit before and was just reading the instructions on the install sheet.. I have a 142gtl that I have not put channels in it so got this for free and want to put it in the radio over the next few days. the kit just did not have the choke in it.
    you did not say but a conformal choke should work to do this mod I guess.
     

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