Target Receiver Gain?

Discussion in 'The Low Bands - 630/2200 Meters - VLF' started by KK5JY, Sep 21, 2018.

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  1. KK5JY

    KK5JY Ham Member QRZ Page

    I'm working on a home-brew receiver for LF, and I'm wondering if anybody has recommendations for a goal for front-end receiver gain? I started with a goal of 80dB, but I'm wondering if 120dB would be useful, or just too much.

    Any suggestions?
     
    Last edited: Sep 21, 2018
  2. N0UU

    N0UU Ham Member QRZ Page

    Gain isn't the right approach. You want the noise capability of the RX to match the noise the antenna presents on that frequency. Most RX have more than adequate NF and at 630M probably you can go directly into the mixer (after filtering!) or the sample for SDR. Multiple articles are out there on what loss distribution you need. The key after loss/gain distribution is solved is what levels you present to the SDR or in the classic RX, to the card/AD converter. Remember that for very LF signals people have written programs to just use the input to the sound card...up to 192 KHz or so.
    I too am curious as to what number on NF and gain to sound card people reply with. Sorry just to speak in generalities!
    N0UU
     
    KK5JY likes this.
  3. KK5JY

    KK5JY Ham Member QRZ Page

    No problem... I have to start learning somewhere. :)
    I don't expect you to do my research for me, but could you recommend a title of one good article like those you have in mind? It sounds like I need to pick up a little terminology, so a starting place would help.
     
  4. N0UU

    N0UU Ham Member QRZ Page

  5. N0UU

    N0UU Ham Member QRZ Page

    KK5JY likes this.
  6. N0UU

    N0UU Ham Member QRZ Page

    Obviously I messed this up: Google the Chadwick article above for the first of the two.
    For an in depth look at noise (Fa) a little bed time reading:
    https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-8-200304-S!!PDF-E.pdf
    You want to have the noise floor of your RX somewhere around Fa. The output to match your decoding device. And the gain results.
    Hope this helps. See you on the air.
    N0UU
     
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  7. KK5JY

    KK5JY Ham Member QRZ Page

    Thanks! I'll start doing some reading.
     
  8. KD8DEY

    KD8DEY Ham Member QRZ Page

    Haven't stared playing with those low bands, but I remember reading somewhere that gain in HF radios was usually concentrated in the I.F. section,
    with gain being typically targeted to be about 20 Db per section in the I.F. stage....
     
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  9. KK5JY

    KK5JY Ham Member QRZ Page

    That's good to know. I had planned for 40dB stages, but that was the voltage kind (the 20 * log10 kind), so 20dB measured as power (the 10 * log10 kind) might be about right.
     
  10. K7JEM

    K7JEM Ham Member QRZ Page

    20 dB is the same gain, whether in power or voltage. 20dB would be 10X the voltage or 100 times the power, assuming fixed impedance. The gain is going to depend on what you are doing after the front end, such as a mixer or detector of some sort.
     
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