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SA extension to 2GHz

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  • Sam Wetterlin
    Hi All, There were some postings recently about using the SA in the 1-2 GHz range to look at harmonics. Here is a simple way to do it: Bypass the cavity
    Message 1 of 2 , Mar 25, 2008
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      Hi All,
      There were some postings recently about using the SA in the 1-2 GHz
      range to look at harmonics. Here is a simple way to do it: Bypass the
      cavity filter and Mixer2, so the output of Mixer1 attaches where the
      output of Mixer 2 used to attach. Now the 10.7 MHz IF2 comes out of
      Mixer 1 instead of Mixer 2 (and there is no IF1). If the first LO is
      tuned to 1050 MHz, thinking it is generating IF2 from an RF input of
      approx. 26 MHz, it will in fact be generating IF2 from 1039.3 MHz and
      1060.7 MHz. In the case of harmonics of sub-1GHz signals, if there is
      a signal at one of those points there is none at the other, so all is
      well. Note that 1060.7 MHz will also generate IF2 when the LO is at
      1071.4. This means the SA display will show every signal twice, like a
      TV image with a ghost, spaced 21.4 MHz apart. When viewing harmonics,
      it is easy to interpret the results--just ignore the left image in
      each pair (or the right, whichever you choose). This would also be
      useful for other purposes, so long as there aren't signals close
      enough to the signal of interest to cause its ghost image to overlap
      with the signal of interest. For example, perhaps with an appropriate
      bandpass filter you could look at an entire GPS band (actually I don't
      know how wide they are) without worrying about interference from ghost
      images; if there are no nearby signals you don't even need the
      bandpass filter.

      This requires just a cable change; the software does not have to do
      anything different as long as you are willing to translate the SA's
      indicated frequencies to the actual 1GHz+ frequencies. You also would
      have no automated calibration for those frequencies. Long term maybe
      the software could accommodate this. (I think our software guy is busy
      right now.)

      Sam Wetterlin
    • Sam Wetterlin
      Ignore my reference to 26 MHz; wrong number. The point is it is some low frequency. Sam W.
      Message 2 of 2 , Mar 25, 2008
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        Ignore my reference to 26 MHz; wrong number. The point is it is some
        low frequency.
        Sam W.

        --- In spectrumanalyzer@yahoogroups.com, "Sam Wetterlin"
        <swetterlin@...> wrote:
        >
        > Hi All,
        > There were some postings recently about using the SA in the 1-2 GHz
        > range to look at harmonics. Here is a simple way to do it: Bypass the
        > cavity filter and Mixer2, so the output of Mixer1 attaches where the
        > output of Mixer 2 used to attach. Now the 10.7 MHz IF2 comes out of
        > Mixer 1 instead of Mixer 2 (and there is no IF1). If the first LO is
        > tuned to 1050 MHz, thinking it is generating IF2 from an RF input of
        > approx. 26 MHz, it will in fact be generating IF2 from 1039.3 MHz and
        > 1060.7 MHz. In the case of harmonics of sub-1GHz signals, if there is
        > a signal at one of those points there is none at the other, so all is
        > well. Note that 1060.7 MHz will also generate IF2 when the LO is at
        > 1071.4. This means the SA display will show every signal twice, like a
        > TV image with a ghost, spaced 21.4 MHz apart. When viewing harmonics,
        > it is easy to interpret the results--just ignore the left image in
        > each pair (or the right, whichever you choose). This would also be
        > useful for other purposes, so long as there aren't signals close
        > enough to the signal of interest to cause its ghost image to overlap
        > with the signal of interest. For example, perhaps with an appropriate
        > bandpass filter you could look at an entire GPS band (actually I don't
        > know how wide they are) without worrying about interference from ghost
        > images; if there are no nearby signals you don't even need the
        > bandpass filter.
        >
        > This requires just a cable change; the software does not have to do
        > anything different as long as you are willing to translate the SA's
        > indicated frequencies to the actual 1GHz+ frequencies. You also would
        > have no automated calibration for those frequencies. Long term maybe
        > the software could accommodate this. (I think our software guy is busy
        > right now.)
        >
        > Sam Wetterlin
        >
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