Rohde & Schwarz R&S FSP Series, Руководство по эксплуатации

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R&S FSP Instrument Functions
LO/IF ports for external mixers - Option R&S FSP-B21
4.282 Operating Manual 1164.4556.12 - 06
Display of mixer products at the same frequency
If the input signal consists of a very large number of spectral components, it will
become more and more probable that two different unwanted mixer products will be
displayed at the same frequency in the test sweep and reference sweep. Such a
case is shown in
Fig. 4.39 .
Fig. 4.39 Different mixer products represented at the same frequency in the test sweep and
reference sweep
The external mixer has been working using 2
nd
order harmonic. The signal recorded
in the test sweep is displayed by trace 1. The IF filter of the R&S FSP is represented
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 3
rd
order har-
monic. Since the frequency axis scaling is based on the 2
nd
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 fun-
damental of the LO signal. Since the frequency axis scaling is based on the 2
nd
order, the mixer product or the resulting diagram of the IF filter is expanded by a fac-
tor of 2.
Automatic identification with a large span is not possible since the two mixer prod-
ucts are displayed at the same frequency. The diagram shown in
Fig. 4.40 is
obtained when examining products with a narrow span using AUTO ID . The user
can easily recognize unwanted mixer products from the clear diagram obtained
using
AUTO ID or SIGNAL ID .
R e f - 3 0 d B m
*
B
R B W 3 0 k H z
V B W 1 0 0 k H z
S W T 2 0 m s
C e n t e r 2 9 . 4 6 8 1 3 3 9 1 G H z S p a n 2 0 0 k H z 2 0 k H z /
1 S A
A V G
2 S A
A V G
- 1 3 0
- 1 2 0
- 1 1 0
- 1 0 0
- 9 0
- 8 0
- 7 0
- 6 0
- 5 0
- 4 0
- 3 0
1
M a r k e r 1 [ T 1 ]
- 4 5 . 0 3 d B m
2 9 . 4 6 8 1 3 3 9 1 0 G H z
n d B [ T 1 ] 3 . 0 0 d B
B W 1 9 . 8 7 1 7 9 4 8 7 2 k H z
T 1
T e m p 1 [ T 1 n d B ]
- 4 7 . 9 9 d B m
2 9 . 4 6 8 1 2 3 6 5 4 G H z
T 2
T e m p 2 [ T 1 n d B ]
- 4 8 . 0 9 d B m
2 9 . 4 6 8 1 4 3 5 2 6 G H z