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R.F. Preamp Gain

Discussion in 'Electronic Design' started by Jamie, Sep 4, 2012.

  1. Jamie

    Jamie Guest

    I am doing a restore for a friend on an old chicken band transceiver
    which is actually in meant shape.. I have a service manual however,
    the receiver seems to be a little weak and the manual does not give you
    enough info to determine if the RF preamp is at full gain.

    I use both my service monitor, HP signal generator and HP RF millivolt
    meter for several references to make sure I had an agreeable reading.

    From what I can gather, I am getting 20 db gain on the R.F. preamp,
    does this sound feasible? If not, I will need to locate a 1 ghz
    transistor to replace it. The transistor seems to check fine DC wise and
    all check points for DC test match the service manual, close enough.

    20 db gain sound correct?

    Jamie
     
  2. Jamie

    Jamie Guest

    it's just a basic RF transformer input with a RF transistor output on
    the collector.. It uses a bipolar transistor. It's very simple.

    The RF gain control comes through the secondary side of the RF input
    transformer where there is 2 back to back clamping diodes to prevent
    over drive accidents.

    The supply side of the primary output RF transfomer does use a
    tantalum cap for the bypass, as such in may other locations in that
    unit. I don't get any stray RF there so I can only amagine it is ok.


    20 db gain


    +--------------------. ,-
    2SC1730L | | )|(
    RF in + --- ++|( RF out
    |/ --- +' '-
    -. ,+-----+--+--------+-| | |
    )|( | | |> +----+
    )|( | | +------+----+ +----+
    -' '+ | + | | | | +
    | V - 1S2473 .-. + | | --- 22n
    | - ^ | | 47n | | | ---
    +-----+--+ 330| | --- | + |
    | | '-' --- - | ===
    .-. | | | ^ .-. GND
    | | --- 1u | | | | |
    10k | | --- === === | | | 100
    '-' | GND GND .-. '-'
    | GND | | |
    | | | 9.34v
    _V_ '-'330
    +----+-|___|+------------+ |
    | |
    | .-. 100k RF level TX switch to inhibit
    +->| |
    | |100k
    '-'RF min
    |
    GND

    Jamie
     
  3. Robert Macy

    Robert Macy Guest

     
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