4.10.- Spectrum Analyser Operating Mode
The Spectrum Analyser mode allows the user to discover the signals present in the frequency band in quickly and easily and to make
measurements at the same time. To select it press key SPECT [21]. The monitor will show a picture like the one described in the next figure.
Figure 17.- Spectrum Analyser mode.
The horizontal lines define the signal level, the broken lines being 5 dB from the solid ones. The level of the top line (80 dB µV in previous
figure), named the Reference Level, can be altered using the Reference level function in the Spectrum Analyser mode functions menu
(section 4.10.1.3).
The signal level for each frequency is displayed vertically, the lower frequencies appearing at the left of the screen and the higher ones at
the right. The amplitude of the lobes is calibrated. In the example in previous figure the noise level is at around 37 dBµV and the lobe with the
highest signal level (second from the left) is at 64 dBµV.
The frequency range displayed (called span from hereon) can also be altered using the Spectrum Analyser mode functions menu.
A vertical broken line, called marker, appears on the spectrum display to identify the tuned frequency.
One of the applications of the MTD 120 operating as Spectrum Analyser is in the search for the best orientation and position of the
receiving antenna. This is particularly important in UHF. Because such frequencies are involved, with wavelengths ranging from 35 cm to 65
cm, if the antenna is shifted only a few centimetres, the relationship between the picture, chrominance and sound carrier frequencies change,
affecting the quality of the picture in the receiver.
If there is an excess of sound carrier, tearing or 'moiré' may appear on the screen due to the frequency beats between the sound,
chrominance and the picture frequencies.
If there is a chrominance carrier defect, then the television colour amplifier must function at maximum gain, which could result in noise
appearing all over the television screen with points of colour that disappear when the saturation control is reduced; in an extreme case, loss of
colour may occur.
4.10.1.- Spectrum Analyser Mode Functions Menu
In the Spectrum Analyser operation mode, pressing key ENTER [5] leads you to the next functions menu.
Figure 18.- Spectrum Analyser mode functions menu.
When press key
[6] active option moves upwards while press key
[6] active option moves downwards.
The downward pointing arrow at the bottom left of the menu means that there are more functions available, to view these press key
[6]. Below we describe the use of each function and its range of values.
FUNCTIONS
Band switching
Span
Reference level
Dual marker
Sweep
Measure bandwidth
80
70
60
50
40
1992.0 MHz
56.9 dBuV
132
TV & SAT Level Meter MTD 120
User Manual
