Anritsu Field Master MS2070A Measurement Manual page 23

Spectrum Analyzer Measurements
The spectrum analyzer has several mixer bands. Depending on the operating frequency, the local oscillator
may be above or below the input frequency. When the local oscillator frequency is below the input frequency,
an increase in the input frequency results in an increase in the IF output frequency. When the local oscillator
is above the input frequency, an increase in the input frequency moves it closer to the local oscillator frequency
and the IF output frequency consequently decreases. The following table shows the bands and indicates where
the LO frequency is, in relation to the RF frequency.
Table 3-2. IF Inversion Bands
RF Band
1
2
3
4
5
6
7
8
9
10
11
12
"Inverted" means that the IF is spectrally inverted from the input (as the input frequency goes higher, the IF goes lower).
"Not Inverted" means that the IF is not spectrally inverted (as the input frequency goes higher, the IF goes higher).
You need to take frequency inversion into account when processing the IF signal. Assuming that the IF has
been processed to yield I and Q data, inversion is easily done by swapping I and Q.
A residual frequency offset of the IF may exist compared to the RF due to the resolution of the first and second
local oscillators. This offset is usually on the order of several kHz, but may be up to 10 kHz or so. To determine
the residual offset, you need a second spectrum analyzer or a frequency counter.
1. Attach a signal source (or antenna) to the spectrum analyzer and set the center frequency to the center of
the signal being received.
2. Set Zero Span from the FREQ/SPAN menu, and then press IF OUTPUT and enable the IF output.
3. Attach a second spectrum analyzer to the IF Out port and set the center frequency to 300 (or 325) MHz.
4. Set the span of the second spectrum analyzer to 100 kHz with the resolution needed to be able to
measure an offset that may be 25 kHz or less.
5. Measure the frequency of the IF signal to see how far the signal is offset from 300 (or 325) MHz.
Spectrum Analyzer MG
Start Frequency (MHz)
0
5350
7200
9200
11100
13000
16500
20400
26950
33810
39900
47000
PN: 10580-00447 Rev. E
3-3 Setting Frequency Parameters
Stop Frequency (MHz)
5350
7200
9200
11100
13000
16500
20400
26950
33810
39900
47000
54000
Spectrum Inversion
Y
Y
Y
N
N
N
Y
Y
Y
Y
N
N
3-5