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Audio gen. RF harmonics

Discussion in 'Electronic Design' started by Genome, Aug 31, 2007.

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  1. Genome

    Genome Guest

    Stop being a twat and get yourself of down the local toilet and snork
    off blokes.

    DNA
     
  2. Tim Williams

    Tim Williams Guest

    So, you want to add the frequency 1.6MHz, or a sideband at 1.6 (4.6 + 1.6 =
    6.2MHz)?

    The first is a linear mixer (resistor, say), the second is a linear
    multiplier.

    I have no idea what you mean by audio frequency. The farthest first order
    sideband that can be produced is +/-20kHz. (Higher order IMD products, from
    a nonlinear multiplier, will give spurs at multiples and so on.)

    Tim
     
  3. LVMarc

    LVMarc Guest


    The process that matches your description is Frequency modulation of the
    RF caRRIER. Say you have an rf carrier of 4.6 Mc, and you take a 20 Kc
    tone and frequency modulate the carrier. And, further, you arrange the
    amplitude and sensitivity such that the 20 KC tone produce a deviation
    of 800 kc. the resultant spectra would look like:

    the carrier,

    surrounded on both side by 20 kc "harmonics" on both sides
    further there will be "harmonics" at 20 40 60 80 etc , spacing, on each
    side of the carrier
    further, they will extend + or 800 Kc on each side, 1.6 mC all together.

    The amthemactical function that describes the placemt and amplitude
    distribution of this "harmonics" often called sidebands, are the
    bessel's function.

    Happy modulating

    marc


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  4. Furthermore, if you modulate the frequency and the amplitude at the same
    time, you can get very peculiar spectrum. However the 20kHz modulation
    is not going to produce a pure 1.6MHz tone in addition to 4.6MHz carrier.


    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
    http://www.abvolt.com
     
  5. I am hoping some mathematical genius can help me with this. I read of
    a process whereby _specific_ harmonic frequencies can be added to a
    fixed RF carrier by mixing it with an audio frequency. Both are
    initially sinewaves, of course.

    What is the mathematical basis for achieving this?

    As an example, say one wants to add a 1.6MHz spectral component to a
    fixed 4.6MHz carrier. What frequency within the audio range would
    achieve this, and how is it determined.

    Thank you greatly for any insight on this matter.

    Mark Jennings
     
  6. When applied to electronic music, this was called the Chowning method.

    Summary at http://www.indiana.edu/~emusic/fm/fm.htm

    --
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  7. Chuck

    Chuck Guest


    If you want to see a 1.6MHz sine wave
    and a 4.6MHz sine wave on one terminal,
    you can combine the two inputs with a
    simple resistive combiner, as has
    already been suggested.

    No harmonics at all will be present at
    the output of the resistive combiner.

    If you want harmonics, the two (or more)
    inputs must pass through a non-linear
    device (mixer or modulator), in which
    case the output (this depends on the
    particular mixer/modulator chosen) will
    consist of the original inputs plus
    their sum and difference frequencies,
    plus sums and differences of harmonics
    of the inputs, such as 3n+m, 2m+17n,
    n+4m, etc.

    In theory, it doesn't matter whether the
    frequencies are audio or RF. In
    practice, the mixer must be chosen to
    accommodate the frequencies to be mixed.

    If this sounds like what you have in
    mind, do a Google search on "frequency
    mixer."

    Chuck
     
  8. Tam/WB2TT

    Tam/WB2TT Guest

    1.6 MHz is not in the audio range; so, just exactly what are you trying to
    do?

    Tam
     
  9. LVMarc

    LVMarc Guest

    chuck,

    the non linear device ie the mixer, will produce the desired sum and
    difference, and then you get the inter modulation products.. I consider
    the IM the "bad" result and distortion. I had thought that the poster,
    really wanted to produce a picket fence of evenly spaced spectra, and he
    described what he wanted best way he could. So the mixer and IM
    distortion will produce sorta what the poster wants but in a "bad" way.
    Te relatively wide BAND FM prodUCes A PICKET FENCE SPECTRA, AT THE
    SPACINGS AND ....DOESNT COUNT ON THE NON LINEAR TRANSFER CURVE OF A
    DIODE FOR EXAMPLE.

    yOU CAN GET INto A WHOLE thread on making wieband, even ly spaced and
    equal(almost amplitude, picket fence spectra creations.. all depends
    what you really want to do, and considering implementation constraints
    to guide the final design optimizations.

    best regards,
    Marco
     
  10. Chuck

    Chuck Guest

    LVMarc wrote:

    snip
    You can call them IM products but they
    are always present in the output of a
    nonlinear mixer. Usually unwanted in a
    mixer's output, but always bad in a
    device intended to be linear.

    I had thought that the poster,

    No way of knowing the OP's intent.

    Chuck
     
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