Promax GV-698, Instruction Manual

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5 DESCRIPTION OF INPUTS AND OUTPUTS
5.1 Composite video output (BNC)
The composite video output is achieved through the VIDEO connector [24]
on the front panel. The polarity of the signal is positive and the synchronisms negative,
the black level being 0 V. The amplitude may be varied by means of the video level
control LEVEL [23] between 0 and 1.2 Vpp. In the "CAL" position, the amplitude is
normalized at 1 Vpp. This signal is very useful in testing B/W and colour video
monitors, linear amplifiers, VCR or any other equipment which operates with a
composite video signal.
CAUTION
This signal must not be connected to any live point in a circuit, but only to
normalized video inputs of 75
Ω
impedance. Any damage produced in the
equipment due to non-observation of this precaution is not covered by the
guarantee.
5.2 Modulated RF output
The modulated RF output (with the video and sound selected) is achieved
through the RF connector [11] on the front panel.
The modulation of the RF carrier by the video signal is achieved by means of
a suitably polarized diode modulator (this achieves double sideband modulation); the
inversion of modulation, positive or negative, is achieved by modifying the polarity of
this video signal. Given that a broadcasting station uses vestigial-sideband
transmission, the correct tuning-frequency corresponds:
- If it is tuned to the TV -> to higher frequency
- If it is tuned to the generator -> to lower frequency.
Incorrect tuning can be clearly distinguished from correct tuning by the
appearance of a low signal/noise ratio, inversions of modulation or lack of synchronism.
The wide frequency margin of the GV-698 permits the selection of 38.9 MHz
(45,75 in USA), which is the intermediate frequency used by TV receivers. It is possible
to connect the modulated signal to the IF stage input and test, in case of failure,
whether it occurs in the tuner or in a later stage.
The possibility of attenuating the RF output has been foreseen for testing the
automatic gain control circuits and the sensitivity of television sets: one three-stage
attenuator, two -20 dB (buttons [9] and [10]) and one -10 dB (button [8]) are
incorporated, permitting a total maximum attenuation of -50 dB (30 µV) in steps of
-10 dB. Normally, a correctly adjusted television set shows an effect of snow in an
image when 30 dB (300 µV) attenuation is selected.
5.3 Synchronisms output
The synchronisms output is situated on the rear panel, through the SYNC.
connector [30]. It serves for the synchronization of monitors with an input for
separate synchronisms, the horizontal and vertical synchronisms are present.
05/96 GV-698