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Lowering the noise figure in a rf preamp

Discussion in 'Electronic Design' started by [email protected], Apr 12, 2006.

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  1. Guest

    Does anyone have any ideas on how to lower the NF in a uhf preamp? I
    have two types
    one had seperate comopnents and the other is a self contained chip.
     
  2. Reduce temperature is the obvious one. Liquid nitrogen (or better).

    --
    Dave K MCSE.

    MCSE = Minefield Consultant and Solitaire Expert.

    Please note my email address changes periodically to avoid spam.
    It is always of the form: [email protected] Hitting reply will work
    for a couple of months only. Later set it manually.
     
  3. John_H

    John_H Guest

    Select a different uhf preamp.
     
  4. Didi

    Didi Guest

    Reduce temperature is the obvious one. Liquid nitrogen (or better).

    Actually LN2 is a bit too cool (though I think I get your point) :).
    In gamma particle detectors - made of a large Ge crystal
    cooled down to liqud nitrogen - the preamp FET is cooled
    to something higher, about -90 C (rather than the whole -190 C),
    they seem to work best there...

    Dimiter
     
  5. Reducing the temperature depends on the type of
    semiconductor. A doped silicon one, aka bipolar
    may stop working when the usually thermally excited
    conduction electrons do not populate the fermi
    surfaces anymore. A FET is a completely different
    story. There the conduction is done by a field
    sensitive channel. FETs can work down to LHE.

    Rene
     
  6. Didi

    Didi Guest

    A FET is a completely different
    Fets are different from bipoar indeed. Perhaps they can
    work down to LHe. For some reason, though, the detector
    manufacturers opt for about -90 C - all I know is this is
    common practice based on extensive experimentation
    over the last few decades. Invent a major noise reduction
    technique in this field based on your knowledge and get
    it sold, I may be among those interested.

    Dimiter
     
  7. Rich Grise

    Rich Grise Guest

    It appears that dry ice (frozen CO2) sublimates at -109.3°F or -78.5°C;
    I've seen it used in an acetone bath to get not quite as cold as LN2.
    Then again, depending on your mounting arrangement, you might not need
    any liquid at all - just drop some chunks into a copper chamber...

    Cheers!
    Rich
     
  8. Raise the antenna gain.
    And its height.

    Shorten the cable between antenna and amplifier.

    Improving the noise figure of a UHF preamp will do little or no good if
    the signal is not there in the first place.

    Measure your input S/N on a VFR or something similar.


    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: http://www.tinaja.com/whtnu.xml email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  9. Doesn't seem to work much with tv satellite receivers.
    Lowering the temperature apparently trashes the gain for no net benefit.

    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: http://www.tinaja.com/whtnu.xml email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
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