Fluke PM5414V - Handbuch (Seite 27)

PM 5414 V OPERATING INSTRUCTIONS 3 - 1 3
11. DEM pattern
Demodulator is a combined test pattern which is divided into four horizontal sections (parts).
The signal contents of the DEM pattern depends on the TV system that is selected.
PAL:
The first section of the pattern consists of two horizontal bars. Bar one contains R-Y and B-Y
information and G-Y is zero. The bar adjacent is a reference bar with no color information, only
50 % luminance or Y signal.
G-Y = 0
A
±(R-Y)
= 0.28
A
+ (R-Y)
= 0.28
A
i ( R - Y )
= 0.28
A
-(R-Y)
= 0.28
Y = 50 %
□
+ (B-Y)
= 0.5
□
±(B-Y)
= 0.5
□
-(B-Y)
= 0.5
□
T(B-Y)
= 0.5
Reference Y = 50 % (*)
PAL
1 ^
I I
Y = 54 %
-I = 0.23 Q = 0
white (Y = 100 %)
A (B-Y) = 0 □ (R-Y) = 0
(*) 54%for PALM
Y = 54 %
-1-0=0.23 1 = 0
black (Y = 7.5 %) J
NTSC
The second section consists of four colored squares with color information according to the
adjacent figure. The 1 st and 2nd square are PAL coded. This section indicates the proper func­
tioning of the color demodulator part.
The third section consists of four squares which are color coded but should not show any color
at a well aligned color television or monitor: all four squares should be grey.
Both R-Y squares are NTSC coded: the R-Y signal does not change direction 180° each line. The
burst signal is PAL coded and ensures normal operation of the PAL switch in a color receiver.
The third and fourth square contain only B-Y signal information, alternating 180° each following
line.
Delay line check:
The third part of the pattern is designed for alignment of the 64 [xs chrominance delay in
amplitude and phase. ’Venetian blinds’ appear when adjustment is needed. It is possible to
distinguish between amplitude and phase faults by noting in which bars these blinds appear.
Since the R-Y signal in square one and two are NTSC coded, the delay line and PAL switch
should eliminate all R-Y information since this information in successive lines of the first two
squares is being subtracted.
When an amplitude error exists between direct and delayed signals, the subtracter output of the
delay line will produce R-Y information in one and two. The action of the PAL switch will cause
the information to be inverted on alternate lines to give the Venetian blind effect.
When a phase error exists between direct and delayed signals, Venetian blinds will show up in
squares three and four. Additionally, they also will appear in the yellowish horizontal bar
(G-Y = 0) of the upper left section of this test pattern.