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Uniden Tempo 2020 / 8010 VFO

Discussion in 'Amateur Radio Modifications' started by kopcicle, Aug 26, 2017.

  1. kopcicle

    kopcicle Well-Known Member

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    Anyone care to explain what the %)*&^(^%& Tempo/Uniden is trying to explain in the 8010 manual when they describe the frequencies of the crystals to be used in the remote VFO ?

    The crystal oscillator of the 8010 accepts 10 crystals for channel A to J . Like the 2020, the crystal frequencies must fall within the VFO frequency range between 9.138 kHz and 9038 kHz. The crystal frequency (fx) for any desired operating frequency is calculated by the following formula



    fx = 9.138 - fF (Khz) where fF is any desired operating within 100 kHz coverage regardless of operating bands...

    For some reason I am drawing a complete blank .
     

  2. nomadradio

    nomadradio Analog Retentive

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    Crystals?

    As in "fixed frequency" crystals?

    That's the only reason for a crystal in the range of the VFO frequency, to take the place of the VFO for fixed-frequency operation.

    To use a fixed-channel crystal in this radio, you still must select the correct one of five 100 kHz band segments and push that button to make that crystal work properly.

    Considering the price of custom-cut crystals, why would anyone care?

    73
     
  3. kopcicle

    kopcicle Well-Known Member

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    The possible use of an ltc-1799 oscillator instead of crystals
     
  4. nomadradio

    nomadradio Analog Retentive

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    Have you tried this chip to see if it's stable enough for your application?

    Looks like too much drift for SSB.

    Might be okay for AM.

    73
     
  5. kopcicle

    kopcicle Well-Known Member

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    Worst case 40ppm does seem a bit outside the pale.
    I have used them before and it really depends on the temperature stability of the resistors oddly enough .
    The oscillator is fairly stable but the multi turn trimmers are temperature sensitive. I've found better stability by replacing the variables with fixed resistors .
     
  6. nomadradio

    nomadradio Analog Retentive

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    Sounds like a job for a 15-buck ChinaBay DDS board.

    The spurious 'birdie' problem would be reduced by the low frequency it would be delivering. That, and the VFO oscillator in that radio doesn't actually mix with transmit or receiver signals. It feeds into the PLL that tunes the radio, and this would remove any 'dirty' stuff from a DDS chip from the radio's actual signal path.

    Looks as if the N3ZI DDS kit would be a workable solution, maybe?

    http://www.pongrance.com/


    Used one on my Kenwood TS530, was stable as a rock. And the 530's PLL setup scrubbed any unwanted stuff from the DDS chip's output. Just had to put a buffer amplifier between Doug's DDS and the radio's external VFO input. His newer board has a buffer amp on it, IIRC.

    73
     
  7. kopcicle

    kopcicle Well-Known Member

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    I've thought about the DDS before when I was doing this
    http://www.worldwidedx.com/threads/...equenting-frequency-mixes-and-a-panda.212836/
    That got shelved for numerous reasons (life and work invaded) . I have several of the evilpay sourced LTC-1799 mounted on mini-boards . I'll get to further testing this winter. BTW I have the math but not the tuning/inductor for all the Ham bands now. It just took building a spread sheet.I also have the best estimates for the pre/driver/final tuning .
    For now it's get the antique working then see what fixed crystals I have and compare them to the LTC-1799 .I suspect that without the buffer amp that used to be the doubler or trippler in the radios that the very square wave will be an issue. Can you say "harmonics" ?
    We'll see ...

    Thank You for the words
     

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