Instrument Functions
R&S
®
FSVA/FSV
523Operating Manual 1176.7510.02 ─ 09
Figure 3-42: Different mixer products displayed at the same frequency in the test sweep and refer-
ence sweep
The external mixer has been working using 2nd order harmonic. The signal recorded in
the test sweep is displayed by trace 1. The IF filter of the R&S FSVA/FSV is represen-
ted at a 3 dB bandwidth of 20 kHz, the real IF bandwidth being 30 kHz. If, however, the
3 dB bandwidth (trace 2) of the signal recorded in the reference sweep is examined, it
will be found to be larger exactly by a factor of 2. This shows that the two products
were generated by mixing with LO harmonics of different orders The signal recorded in
the test sweep was generated by mixing with 3rd order harmonic. Since the frequency
axis scaling is based on the 2nd order, the mixer product or the resulting diagram of
the IF filter is compressed by a factor of 2/3. The signal recorded in the reference
sweep was generated by mixing with the fundamental of the LO signal. Since the fre-
quency axis scaling is based on the 2nd order, the mixer product or the resulting dia-
gram of the IF filter is expanded by a factor of 2.
Automatic identification with a large span is not possible since the two mixer products
are displayed at the same frequency. The diagram shown in Figure 3-43 is obtained
when examining products with a narrow span using "AUTO ID". You can easily recog-
nize unwanted mixer products from the clear diagram obtained using "AUTO ID" or
"SIGNAL ID".
Instrument Functions – External Mixer (Option R&S
FSV-B21)
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