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How do I measure FM or PM deviation and rate on my vector signal analyzer (VSA)?: Z9 h; A2 U% C' k
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These measurements may be made in vector mode or in analog demodulation mode on the 89410A, 89441A or the 89600S family of vector signal analyzers.' A- Y7 O( D9 L* u
1) In vector mode, center the carrier in the span, and set the span to include all significant sidebands of the modulated signal. In the 89600S example below, the signal generator is set up for a carrier 1GHz, a rate of 10kHz (sine wave) and a peak deviation of 100KHz. The analyzer is set up for a center frequency of 1GHz, a span of 500kHz, and the default number of frequency points (801 for the 89600, 401 for the 89400). Set the range so that the OV1 message just disappears.
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8 S/ r/ b7 |+ H: X! r2 oSet up the B (bottom) trace for Ch.1 Main Time with a format of Group Delay. This format puts frequency on the Y axis and time on the X axis. Now pause the signal and place a marker on the peak of the time domain waveform (B trace). Set the offset marker for the opposite peak, and read the peak-to-peak deviation from the marker result at the bottom of the display. In this example, the marker reads 200.46 kHz. At the same time, the marker also reads the half period of the modulating sine wave, 50uS. Double this result and take the reciprocal for the FM rate: 1/(2*50µS) = 10kHz.
3 s L- e V( g5 u! f& A; tYou may also display the carrier frequency by selecting Markers > Calculation and clicking the Analog Demod Carrier radio box on the 89600S, or Marker Function > demod carrier on the 89400.- e! N- ?3 H" n9 e6 n
This same method may be used for phase modulation. This method works because the VSA IQ detection stage acts like a heterodyne mixer to extract the modulating signal.& _9 C: j" T5 j" m i' P! H
2) In analog demodulation mode, using the same center frequency, span and range as above, select FM Demod and FM Carrier Frequency from the Analog Demod Properties menu. Note that trace A data must now be Ch.1 FM Spectrum and trace B is Ch.1 FM Main Time. In the B trace, the Y axis again shows frequency.) i, M* d Q1 K# I- H6 ^1 ~
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Pause the signal and place a marker-to-peak in the spectrum trace A for a marker result of the FM rate, 10kHz. Format the B trace to Real data, place a marker on the peak of the signal, activate the offset marker and place it on the opposite peak for the peak-to-peak deviation. The marker result in this example is 200.47 kHz peak-to-peak deviation.
3 ]- u% _! _+ K4 [2 r4 Z3 c6 jHere is the same signal demodulated on the 89441A. The marker results are displayed along the top of each trace., W! C- z d$ J; i z. E7 X
' z, {: ?- V- J/ ^7 x8 M6 U5 kAgain, the same methods may be used for PM. Here is a phase demodulation on the 89441A (below). Note that the Y axis of the B trace is in units of radians, and the marker result is peak-to-peak deviation in radians.- `( i; E- N+ u7 z, h7 U. s
' H4 ~3 S$ I" Y% E; r8 A1 ]Neither of the VSA’s can measure stereo FM deviation in the analog demodulation mode.
: B: z! U" i$ N1 b |, R$ NIn these examples, both the 89400 and the 89600S vector signal analyzers display results for FM or PM deviation and rate in either the vector mode or the analog demodulation mode. |
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发表于 2019-6-23 08:00
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发表于 2019-6-25 08:48
