• Spectrum Harmonic Demo circuit

    From G8MNY@21:5/101 to TECH on Fri Jul 19 10:52:53 2019
    R:190719/0943Z 5823@GB7YEW.#79.GBR.EURO LinBPQ6.0.18
    R:190719/0943Z @:GB7CIP.#32.GBR.EURO #:12857 [Caterham Surrey GBR]

    From: G8MNY@GB7CIP.#32.GBR.EURO
    To : TECH@WW

    By G8MNY (Updated May 09)
    (8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

    Being involved with ham training, I have been doing all the technical demos including AM & FM (Signal Generator) & this one for harmonics....

    ┌────────┐
    50Ω│SPECTRUM│ ┌───────┐
    Bypass ┌─┤ADAPTOR ├─┤ X-Y │
    ┌──────┐ ┌──────┐ ┌──────────┐ │ │0-90MHz ├─┤DISPLAY│
    │RF SIG│ │DIODE │ o┘ ┌──────┐ │ │ └────────┘ └───────┘
    │ 6MHz ├──┤PROBE ├──o─>o──┤ VIDEO│ └o │┌─────────┐
    │ 1V │ │INSERT│ │ WALL ├──o<─o───┴┤ SCOPE │
    └──────┘ └──────┘ │FILTER│ T│WAVEFOREM│
    └──────┘ └─────────┘

    I cheated with the use of a diode probe (series schotky diode for UHF) insert to produce a poor signal when the sig gen is set to 1V output. This caused the RF sine wave is bent enough to see the harmonics on 6MHz on a scope (>20MHz) & the diode output is terminated into 50Ω by the spectrum analyser.

    The filter I had is an 8 section M derrived video LPF & is 40dB down @ 8MHz, but only 2dB down @ 6MHz. But any suitable filter will show the benefits of a LPF after a harmonic rich source.

    SPECTRUM DISPLAYS

    NO FILTER WITH FILTER
    dB f1 Rich harmonic spectrum dB f1
    0 ┤ │ f2 0 ┤ │ Cleaner
    -10 ┤ │ | f4 -10 ┤ │ Spectrum
    -20 ┤ │ │ f3 | f6 -20 ┤ │
    -30 ┤ │ │ │ │ f5 | f7 f8 -30 ┤ │
    -40 ┤ │ │ │ │ | │ . | -40 ┤ │
    -50 ┤ │ │ │ │ │ │ │ │ -50 ┤ │ f2
    -60 ┴───┴───┴───┴───┴───┴───┴───┴───┴─>F -60 ┴────┴────┴──────────>F
    6 12 18 24 30 36 42 48MHz 6 12MHz


    SCOPE DISPLAYS

    /''\ /''\ /'`\ /'`\
    | | | | | | | |
    RF _▌ ▐______▌ ▐____ ▌ ▐ ▌ ▐
    ▐ ▌ ▐ ▌
    | |
    Distorted RF With Filter \../



    See also my buls on "SSB Demo circuit", "Scope RF Trick", "Tuned Circuit Scope Demo" & "Oscilloscopes".


    Why don't U send an interesting bul?

    73 de John G8MNY @ GB7CIP


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    * Origin: HAMRADIO telnet lu9dce.dynu.com (21:5/101)