Agilent Spectrum Analysis Basics - Agilent Technologies
Agilent Spectrum Analysis Basics - Agilent Technologies
Agilent Spectrum Analysis Basics - Agilent Technologies
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External harmonic mixing<br />
We have discussed tuning to higher frequencies within the spectrum analyzer.<br />
For internal harmonic mixing, the ESA and PSA spectrum analyzers use the<br />
second harmonic (N=2 – ) to tune to 13.2 GHz, and the fourth harmonic (N=4 – )<br />
to tune to 26.5 GHz. However, what if you want to test outside the upper<br />
frequency range of the spectrum analyzer? Some spectrum analyzers provide<br />
the ability to bypass the internal first mixer and preselector and use an<br />
external mixer to enable the spectrum analyzer to make high frequency<br />
measurements 2 . For external mixing we can use higher harmonics of the<br />
1 st LO. Typically, a spectrum analyzer that supports external mixing has two<br />
additional connectors on the front panel. An LO OUT port routes the internal<br />
first LO signal to the external mixer, which uses the higher harmonics to mix<br />
with the high frequency signals. The external mixer’s IF output connects to<br />
the analyzer’s IF IN port. As long as the external mixer uses the same<br />
IF frequency as the spectrum analyzer, the signal can be processed and<br />
displayed internally, just like any signal that came from the internal first<br />
mixer. Figure 7-13 illustrates the block diagram of an external mixer used<br />
in conjunction with a spectrum analyzer.<br />
External harmonic mixer<br />
Input<br />
signal<br />
Atten<br />
3 GHz<br />
3.9214 GHz<br />
321.4 MHz 21.4 MHz<br />
Analog or<br />
digital IF<br />
Input<br />
signal<br />
3 - 7 GHz<br />
3.6 GHz<br />
300 MHz<br />
Preselector<br />
321.4 MHz<br />
Sweep<br />
generator<br />
Display<br />
Figure 7-13. <strong>Spectrum</strong> analyzer and external mixer block diagram<br />
2. For more information on external mixing, see<br />
<strong>Agilent</strong> Application Note 1485, External Waveguide<br />
Mixing and Millimeter Wave Measurements with<br />
<strong>Agilent</strong> PSA <strong>Spectrum</strong> Analyzers, literature number<br />
5988-9414EN.<br />
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