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Adding Frequency Counter to Cobra 148 GTL with front panel mic.

Discussion in 'CB Radio Modifications' started by 8113 Northern MN, Jun 19, 2014.

  1. 8113 Northern MN

    8113 Northern MN Active Member

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    Ive been searching the internet for days upon days searching for some sort of instructions on hooking up a frequency counter to my Cobra 148 GTL with a front mounted mic hookup. Since most frequency counters have the same pattern of wires I havent been using the particular brand of F.C in my search (Connex Fc-390) but all I keep coming up with is a wiring diagram for a side mount mic version of the 148gtl.

    Does anyone have an instruction picture or some sort of diagram laying around in a hidden place to help me out here?


     

  2. Robb

    Robb Yup

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    The front mic 148 uses the same tuning specs as the side mic 148 does.
    So the right FC meant for an earlier radio should work and hook up/work the very same way.
     
  3. 8113 Northern MN

    8113 Northern MN Active Member

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    It isnt the tuning specs that Im concerned about. Its the actual placement of the wires. Ive been unable to come up with a front mic board layout/diagram picture.

    On the FC-390 there are 6 wires:

    1) Black: ground
    2) White: VCO O/P
    3) Brown: ground
    4) Red: VCC
    5) Orange: USB B+
    6) Yellow: LSB B+


    However, I have no clue where these are located on the board. The Front mic and side mic boards are laid out differently so I havent been able to match it up.
     
  4. Robb

    Robb Yup

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    The Defpom FC390 Mods page

    Power, ground, and coax wire goes to TP1 IIRC.
     
    #4 Robb, Jun 19, 2014
    Last edited: Jun 19, 2014
  5. sonoma

    sonoma Sr. Member

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    see if this site helps you. the part locations are basically the same on both boards.

    Galaxy Radios FC347 Service Manual
     
  6. 8113 Northern MN

    8113 Northern MN Active Member

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    I am sorry perhaps I havent been clear.


    I know everything about the actual Frequency Counter and what the wires on it are. I am looking for a diagram showing me where on the radios board these wires are to be connected to. I am unfamiliar with the Cobra 148 GTL front mic style's PCB board and need to know exactly where to solder the wires.

    Sorry for the confusion and hope this helps someone find me some info!
     
    Kangaroo-266-Doug likes this.
  7. sonoma

    sonoma Sr. Member

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    the info I sent you shows where to hook the wires. do not know what else you are wanting. the same locations on the front mic and side mic are the same. there is a picture showing you where to hook them. here is the layout of the ranger 296 and cobra 148 from the link I sent you.

    http://www.cbtricks.com/radios/galaxy/fc347/148gtl_fc347_wiring.htm

    just like the uniden grant XL and the grant LT. one is a side mic and the other a front mic. both boards are the basic same.
     
  8. 8113 Northern MN

    8113 Northern MN Active Member

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    The Cobra 148 GTL front mic and side mic PCB boards are different. The link you sent I have found before. Like for instance at the bottom where the lines arch in the middle, on the Front panel version of the Cobra 148 GTL....there is no arch and the lines just go straight. That page is super helpful as it does say what the individual wires are suppose to be hooked to...I need a diagram showing where those spots such as the VCO o/p and such are located on my version of the board.
     
  9. 8113 Northern MN

    8113 Northern MN Active Member

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    Here is my corner of the board. See how its different front the side panel version which your picture shows?


    [​IMG]
     
  10. sonoma

    sonoma Sr. Member

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    all you have to do is use a volt meter to check for the 3 wires that go for lsb am and usb 8 volts and then the vco area. it is all in the same location just the board layout looks a little different from one manufaturer to another. such as malaysia the taiwan then chains.. some of the traces change how they are shapped but still in the same area of the board. I do not have one like yours here to look at so someone will have to have one and wire it up for you to see.
    that is what I did in about 2005 for a grant LT since everyone said it was different from the XL. Defpom's site has the pic of the LT. maybe it is the same as the cobra.
     
  11. sonoma

    sonoma Sr. Member

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    see if the grant LT will load here.
     

    Attached Files:

  12. Robb

    Robb Yup

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    Yes, the boards are slightly different. They look different too. But the FC hookup goes to the same place - TP1. Modding the FC so it works on one of the radios has already been provided by Sonoma, he has done this mod a bunch..
     
  13. sonoma

    sonoma Sr. Member

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    also you can trace the wires from the usb,lsb and am switch which will only have the 8 volts to it for each band for the 3 band wires. you can then use a freq counter to check on the bottom of the vco for the right hookup for the freq read out. that is the way I do it to add a freq counter to a radio that does not have the picture for you to follow to install a counter. that was why I did the LT a few years ago because every one back them kept saying you could not put one on it since the board looked different. like I stated I do not have a front mic cobra to help you out any farther. sorry this is all the info I have for you.
     
    Shadetree Mechanic likes this.
  14. 8113 Northern MN

    8113 Northern MN Active Member

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    After much trial and error and some tuning me and a buddy were able to get the Connex FC-390 working on the front mic Cobra 148 GTL successfully. It took awhile and some tinkering but it is working.

    However , I have encountered some strange problems since it happened. First of all, my RX seems way down. Generally when i have the radio on and am listening on 38 LSB there is a considerable amount of blank static white noise that i will have to turn my clarifier up in order to hear. After the install I am able to tun the rf gain ALL the way up and barely hear any static. This concerns me a bit as I love shooting skip and wanna be able to hear all the stations out there during peak hours.

    My second issue....When installing the counter I looked through various "guides" i found. SOME stated to use a 68pF ceramic resistor at the end of the white wire that connects to the VCO, SOME stated it wasnt needed and some stated that you didnt even need to use EXACTLY a 68 , that using a bit higher would even work. I was never able to find a reason for this resistor and what the effects of using it/not using it are. We ended up only having a 100pf resistor on hand and used it. Can someone shed light on what that resistor is for and if it may be causing my RX issues. And if not, any idea what could be. Once ive solved this little issue with RX I will post pictures on the exact places on the front mic PCB version of the Cobra 148 GTL so others can successfully do this mod. Thanks!
     
    Kangaroo-266-Doug likes this.
  15. Robb

    Robb Yup

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    You mean a coupling cap?
    Yes.
     

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