Promax US TV EXPLORER II, Руководство пользователя

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USER’S MANUAL. US TV EXPLORER II
Page 70 01/2008
The signal level for each frequency is displayed vertically, the lower frequencies
appear 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 25
dBµV and the lobe with the highest signal level (third from the right) is at 70 dBµV.
In the case that the equipment detects saturation on RF input due to an excess of
signal, it will appear the icon in the Spectrum Analyzer mode and the icon in
the TV mode to indicate this situation. The user must increase the Reference Level in
order to activate an additional attenuator and to avoid the input saturation.
The frequency range displayed (called span from hereon) can also be altered
using the horizontal cursors [6] key. Therefore enables selecting the displayed
screen frequency range in Spectrum Analyzer mode between Full (the entire band),
500 MHz , 200 MHz , 100 MHz , 50 MHz , 32 MHz , 16 MHz and 8 MHz (the latter one only
in terrestrial band).
A vertical broken line, called marker , appears on the spectrum display to identify
the tuned frequency.
One of the applications of the US TV EXPLORER II operating as Spectrum
Analyzer 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
centimeters, 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 color amplifier must
function at maximum gain, which could result in noise appearing all over the television
screen with points of color that disappear when the saturation control is reduced; in an
extreme case, loss of color may occur.
5.16.1 Markers
( Only in Spectrum Analyzer mode ). The marker in red color indicates the central
frequency or tuning frequency, which can be moved by means of turning the rotary
selector [1] as well in channel as in frequency tuning mode [24].
When monitoring a digital signal spectrum also appears two additional markers in
white color, which indicate the bandwidth of the digital channel (See previous Figure).