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Cobra 2000GTL Low Channel Mod??

Discussion in 'CB Radio Modifications' started by dx77HML, Feb 20, 2013.

  1. dx77HML

    dx77HML Member

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    I have a 2000gtl and i need it to go down to 26.775.I see a lot of mods for it but it shows it will only go down to 26.815.It already had a crystal mod in it for 40 above 40.It has the fat 11.3258 main crystal in it.What crystal would get it down to 26.775 and where could i find one if so?
    Thank's,


     

  2. RADIOOMAN

    RADIOOMAN Active Member

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    I would do a search on the web for a "EXPO 100 kit".
    You might be able to find someone that has them for sale.
    It was a kit that had two crystals with it and you had to solder it into the circuitry of the radio.
    It would give an additional 40 below the FCC 40 and 40 above.

    It looks like the crystal frequency you are looking for is 11.1758.

    http://www.kenselectronics.com/lists/cbxtal.htm
     
    #2 RADIOOMAN, Feb 20, 2013
    Last edited: Feb 20, 2013
  3. sonoma

    sonoma Sr. Member

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  4. melaza

    melaza Member

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    Hi, replace 11.3258 to 11.1125. Works from 26.175 ~ 28.045.

    Greetings from the Caribbean!(y)
     
  5. dx77HML

    dx77HML Member

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    melaza,i tried changing the crystal to 11.1125 but it did not work!This radio already has the MB8719 PLL in it.With the 11.3258 main crystal is has regular 40 channels.Another crystal was added thru a relay that switches the main crystal to another for 40 above ch.40.I believe the crystal will have to be the 11.1758 as RADIOMAN stated to obtain the low channels.I dont need the uppers,i just need the lowers.Thank's for all of the replies and i will update after i obtain the crystal and install!
    Thank's
    Danny
     
  6. melaza

    melaza Member

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    Hi, with the 11.1125 just isolate pin 10 from ground and you get 40 low channels (26.325~26.765). Switch pin 11 to ground and you get more low channels. If you uses 2 switches, one for each pin you get the low channels starting from 26.175. I'm late to work. See you later.

    :sneaky2:
     
  7. dx77HML

    dx77HML Member

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    Pin 10 is already isolated from ground in the 2000GTL.I did not try to switch pin 11 to ground though.I believe the 148GTL would work as pin 10 is grounded on the board.I'm gonna order the 11.1758 crystal today.
    Thank's
    Danny
     
  8. dx77HML

    dx77HML Member

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    I obtained the 11.1758 crystal and installed it on a small circuit board with a trimmer capacitor.Installed a small relay on bottom of the main at the original crystal position.Hooked the main crystal and 11.1758 up through the relay and switched the realy on PA/CB switch.I have 40 below now with the frequemcy of 26.775 like i wanted.Thank's to all for the info!!
     
  9. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    There is an easier way to get the lowers if you so desire, without the need to use another crystal. If you want info, I'll gladly post it here on this thread.



    ~Cheers~
     
    Joel likes this.
  10. RADIOOMAN

    RADIOOMAN Active Member

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    I have a Cobra 2000 that I modded without crystals and it will cover 26.815 (-7.5kc) to 28.085 (+6kc)
    Exit 13: I am interested in the post you offer.
    Thanks
     
  11. RADIOOMAN

    RADIOOMAN Active Member

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    Pretty cool.
    That was a good idea to use a relay and the PA/CB switch.
    Clean mod without drilling holes and adding switches.
    I am curisous, if you don't mind to tell us, where you got the cyrstal.
    I am just curious about the 'behind the scenes' info.
    Thanks

    I have a Cobra that I moded with switches only and it goes from 26.815 (-7.5kc) to 28.085 (+6kc) and I added a rotary switch by wich I can select one of the program lines of the PLL chip and with this and and added DPDT relay I can make it operate in "SPLIT-MODE".
    (the added relay allowed me to have the split frequency mode and also allows recieve audio with no micorphone)
    But it does not matter what this radio looks like because it came out of a trash can after the previous owner got mad and threw it from the desk and then proceeded to kick the shit out of it.
    Busted up the front panel pretty bad.
    I cobbled things back together and then added the extra switchs to a small panel I screwed to the front of the radio below the factory switches on the RHS.
    I have used this radio for about 12 years now.
     
  12. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    The MB8719 has a 192 channel capability. My method requires you to change out the loop mixer crystal, but only 1 crystal is needed to achieve the full 192 channels. However the TX and RX can't be broadbanded enough allow full coverage, but would be plenty wide enough to get more of the lowers if you so desire.

    Change out the 11.325 mixing crystal, and install an 11.1125 mixing crystal in its place. Now, with that crystal in place, with the standard PLL modification, you'll get 26.175-27.445. The way to get uppers from there, is to take pin 10 of the PLL and tie it to pin 17. This pin has approximately 1/2 of the PLL control voltage present. Putting pin 10 to pin 17 will get you 27.605-28.045, another bank of 40.

    Sometimes you can just jump a wire directly over, sometimes you can't. If you don't get 27.605-28.045 with just the wire, then you have to install a 1N4148 switching diode inline, cathode (banded side) goes to pin 17, anode side goes to pin 10. When you confirm that you can get 27.605-28.045, you can wire this jump to a SPST switch, and toggle it from there.

    Give this a try, let us know how you get on.

    ~Cheers~
     
    #12 ExitThirteen, Mar 8, 2013
    Last edited: Mar 8, 2013
    Robalo likes this.
  13. RADIOOMAN

    RADIOOMAN Active Member

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    Ok, great.
    Thank you
    I won't be doing anything like this soon but maybe in the future.
    But it's always nice to know what your options are.
     
  14. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    No problem. Enjoy!



    ~Cheers~
     
  15. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    UPDATE:

    Another way to do this mod is to use an LM7805 +5V regulator IC with a 1N4001 rectifier diode in series to pin 10 of the PLL. That way the voltage to pin 10 is isolated and regulated. You may also have to install a small 1K trimmer pot in series to adjust the voltage until the PLL "locks" onto the "extra" band of channels.


    ~Cheers~
     
    LeapFrog likes this.

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