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Full 10M (and above) coverage for EPT6900XX chassis

Discussion in 'CB and Export Equipment and Accessories' started by VA3ES, Sep 3, 2011.

  1. VA3ES

    VA3ES Old Buzzard

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    I have been contemplating modifying my radios wiith the EPT6900XX chassis (General Grant, Superstar SS158EDX, RCI 69FFC2 etc.,) to allow full coverage to 29.700 on 10M. This small modification will simply shift the entire range from the original 24.265MHz - 29.655MHz up to 24.705MHz - 30.095MHz, thus allowing full coverage to 29.700MHz on 10M, while still covering the 12M band.

    I would simply change out the existing X2 crystal (15.360MHz) to 15.800MHZ. I don't believe alignment would be required.

    (I'm also working on a scheme to allow 100KHz repeater splits. This might require another crystal either diode or relay switched in TX.)


     
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  2. Robb

    Robb Yup

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    Uhhhhhh . . . . I definitely would re-align it . . .
    :whistle:
     
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  3. VA3ES

    VA3ES Old Buzzard

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    Really? All I'm doing is shifting the range up by 440 KHz. I would be doing that by simply changing bands, and we don't align the radio when changing bands.

    I'll check it out anyway... RX sensitivity and TX power anyway... just to be sure! ;)
     
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  4. Robb

    Robb Yup

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    Remember; this is the reference oscillator we are talking about here . . .
    I'm sure you have seen the freq expansion boards for Cobra 29's that use multiple crystals. The better expansion boards also include a separate trimmer capacitor for each crystal so that it stays in tune when flipping to a different band/crystal.

    Yes; I would make sure that the voltage is also correct when shifting the core freq of the PLL, as it will shift some. Doubtful that it will become unlocked; but then again - it might too. Depends where the voltage is set. Then I would re-tune the reference oscillator to ensure that is on target. Guess it all depends on how much accuracy you demand from your gear.
     
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    Last edited: Sep 3, 2011
  5. VA3ES

    VA3ES Old Buzzard

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    Actually, we will be checking to make sure the VCO voltage is within tolerance. I'm not sure that a trimmer is required for the X2 reference, as there is none to begin with. Besides, we can net the frequencies as required with the coils, according to the manual. Nothing that any competent tech wouldn't do.
     
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  6. jazzsinger

    jazzsinger Bullshit Buster

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    Me Too.


    you don't realign when changing bands because its already aligned within that bandwidth, but if you shift it all up 440 khz then its going to be out of tune on the top end which it wasn't previously aligned for,

    bare in mind many of these chassis are working at their bandwidth extreme already, when you move past the previous tuning you may get the vco refusing to lock, as well as uneven tx power/rx sensitivity.

    even if i was moving a 40 ch set from mid band (fcc) to high band to cover 27.555 i would retune it.
     
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  7. Highlander_821

    Highlander_821 Amour d'Ecosse

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    I had Richard Byrd do this for my DX2517. He did do a full alignment. Power on 10 meters is a little lower than 11. More like 25-30 watts instead of 35-45 on 11. That is just a limitation of the chassis. No problems with the VCO on this unit.

    I have it connected to a sound card IX and have run SSTV on it. PSK31 is a problem because of drift. People have to chase me all over the waterfall, lol.
     
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  8. VA3ES

    VA3ES Old Buzzard

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    OK, OK!! You guys have convinced me! Sheesh! Such sticklers for accuracy and precision! :rolleyes: (Actually, I hope I can actually get the extra 440 KHz bandwidth out of it. In fact, all I really need is the extra 45 odd KHz, but that extra 300 KHz is a bonus for receiving purposes.)
     
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  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Better check the frequency mixing scheme before ordering a crystal. If that X2 comes into play then you will want a crystal 220 KHz higher and not 440 KHz as the final product will be the difference X2.I once changed a reference crystal by 105 KHz and ended up moving down 210 KHz for the same reason which was a bonus in the end as it moved everything below ch.1. It was a X2.
     
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  10. VA3ES

    VA3ES Old Buzzard

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    I am making a supposition about the new crystal frequency. These are all 12-band radios which use a 15.360 MHz crystal (X2). In the 6-band radios such as some Galaxy's and the Voyage VR-9000, the X2 reference is originally a 14.010 MHz. To move them up, the factory recommended crystal is 15.360 MHz. I calculated the frequencies by taking the lowest frequency available with the original 14.010 crystal, and subtracting that frequency from 15.360 which gave me 1.35Mhz. The new 15.360 rock puts the radio on 26.965 Mhz for Ch1, Band A, and covers up to 29.655 Mhz. (Ch40 Band F) exactly 1.35 Mhz above the old coverage.

    Using that baseline, which is a pure arithmetical addition formula, I calculated that the new crystal to be 15.800MHz.
     
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  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Good enough Ed. I just wanted to point that out so you don't order a crystal that is not what you thought it was. It has happened to people quite often in the past. it sounds like you have it figured out. (y)
     
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