Sequerra 1 Owner's Manual - page 14
D E T A I L E D D E S C R I P T I O N O F SCOPE
A t h o r o u g h understanding o f the i n f o r m a t i o n shown by the oscilloscope's trace w i l l give an
appreciation o f w h a l is being broadcast plus the q u a l i t y o f the broadcast. T h i s presents an o p p o r
t u n i t y t o make allowable adjustments, w i t h t h e tuner and antenna, to achieve the best possible
reception o f receivable programs. A l l scope measurements and trace i n f o r m a t i o n are a p p r o x i m a t e .
T h e y are used t o establish references and are n o t designed for hairline accuracy.
The cathode ray display tube requires greater w a r m - u p t i m e (about 3 0 seconds) than the dis
plays before the trace becomes visible.
T h e oscilloscope display d i m s a u t o m a t i c a l l y whenever the trace reduces t o a " d o t " (at low or
n o a u d i o signal levels). T h i s a u t o m a t i c d i m m i n g a c t i o n extends the life o f the cathode ray tube and
reduces the possibility o f accidently b u r n i n g the screen phosphors.
Panoramic — I n this m o d e the scdpe displays all stations broadcasting w i t h i n a 2 M H z spec
t r u m . (1 M H z each side of the tuned f r e q u e n c y ) . T h e height o f the pips indicate the relative signal
strength o f the stations. The noticeable m o t i o n o f the pips is the result o f the material being broad
casted plus m u l t i p a t h . T h e pan response is flat at the center a l t h o u g h n o t across the e n t i r e 2 M H z .
This w i l l cause some slight d i m i n i s h i n g o f t h e height o f the pips as they are t u n e d across the band
away f r o m center frequency. T h e height o f t h e pips indicate the relative signal strength o f the
stations and corresponds to the a p p r o x i m a t e height o f the trace o f the tuning display (second push
b u t t o n ) . T h i s is just an a p p r o x i m a t e height match as the center vertical line o n the pan display has a
d y n a m i c range o f a p p r o x i m a t e l y 1 0 0 d B . T h i s is the result o f some slight compression at the t o p and
displacement at the b o t t o m . The vertical center line on the graticule delineates the center fre
quency. The t w o vertical lines on either side o f the center line are spaced at intervals o f 4 0 0 kHz.
This spacing corresponds to the FCC spacing o f alternate stations o n the b a n d w i d t h . Adjacent
stations f a l l m i d w a y between the alternates at 2 0 0 k H z spacings, and w h e n the set is tuned w i t h a
p r i m a r y station o n the center line, the alternate stations w i l l be o n the vertical lines, w h i l e the ad
jacent stations w i l l fall between the lines.
A three-pointed trace represents a s t a t i o n w i t h a n SCA subcarrier. Some F M stations simul
taneously broadcast a Subsidiary C o m m u n i c a t i o n s A u t h o r i t y (SCA) signal on the same carrier fre
quency as their regular broadcast. SCA broadcasts are privately sold t o commercial users such as
restaurants, offices, stores, etc., and c o n t a i n n o c o m m e r c i a l advertising.
NOTE:
A l l spectrum analyzers p r o d u c e a v a r y i n g n u m b e r o f ambiguous and erroneous displays.
T h e Panoramic Display in the M o d e l 1 T u n e r is n o e x c e p t i o n . T h e types o f erroneous displays that
y o u may expect are listed as f o l l o w s :
1. Image Responses: A l l stations having a signal strength o f greater than 5 0 0 0 microvolts w i l l
produce an image response in the display precisely 4 . 8 M H z above the station.
2. Spurious Responses: These responses, in this t u n e r , are a t t r i b u t e d mainly t o the d y n a m i c range
l i m i t a t i o n s o f the system. T h e d y n a m i c range upper threshold is 1 0 0 , 0 0 0 microvolts. Signal
i n p u t greater than that produces significant displacement o f the base line as w e l l as a series of
side band m o d u l a t i o n p r o d u c t s .
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