Tektronix 2715, User Manual

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Spectrum Analyzer Menus
6–56
2715 User Manual
NOTE . Because of the FM demodulator bandwidth, the modulating signal used in
the deviation monitor mode should consist of normal program material or a
single tone in the audio frequency range.
The foregoing technique provides a quick look at unidirectional frequency
deviation. The carrier frequency is at the reference level, and a downward
excursion represents a deviation below the carrier. If the FM spectrum is
symmetrical, the peak-to-peak deviation is twice the unidirectional amount. In
the example above, 7 divisions is 70 kHz (at 10 kHz/div), and the peak-to-peak
deviation is approximately 140 kHz.
To see the deviation in both directions, try the MAX HOLD technique outlined
in Measuring Occupied Bandwidths on page 6–50. For extremely accurate
deviation measurements, the Bessel null approach should be used; see Tektronix
application note 26W-7037-1, Spectrum Analyzer Fundamentals.
DEMOD
100.0MHz (AUTO SWEEP) ATTN 0DB
18.8DBMV VF 300KHz
1.0MHz/ 10 DB/
300KHz RBW (AUTO)
The DEMOD menu provides a means of listening to AM or FM modulation on
the signals being analyzed and activating the video monitor mode.
Listening to signals often helps to identify the source. A built-in speaker is
provided, but if higher fidelity is needed, or if you are using the 2715 in a noisy
location, headphones can be used. A 1/8 inch miniature phone jack is located
near the front of the right side of the 2715.
1. Connect a short antenna or CATV tap to the 2715 input as outlined in
Appendix B: Broadcast AM, FM, and TV Signal Sources.
2. Ensure that the calibrator is turned off.
3. If necessary, adjust the reference level until you can see individual signal
peaks in the 88 to 108 MHz FM broadcast band.
If you do not have broadcast FM in your area, you can tune to a TV station
audio carrier.
4. Tune the 2715 until a strong signal is centered.
Listening to FM
Transmissions