Sequerra 1 Owner's Manual - page 15
3. Cross m o d u l a l i o n p r o d u c t s d u e t o the o u t o f band signals i.e.. excessively strong television
signals b e l o w the F M band and excessively strong a i r c r a f t signals above the F M band may
produce spurious responses.
4. Clandestine F M transmitters i.e., bugging devices, r a d i a t i o n f r o m other F M tuners, and other
sources o f electromagnetic r a d i a t i o n w i t h i n the b a n d w i l l be read as responses in the Panoramic
Display.
Tuning — T h e oscilloscope trace f o l l o w s an a p p r o x i m a t e t r a p e z o i d . Spinning the tuning k n o b
fast w i l l give an idea o f the band pass p a t t e r n . Signal strength is indicated b y the relative height o f
the trace above the inter-station noise level ( t h e l o w e r a n d heavier h o r i z o n t a l path of the trace). T h e
center graticule line displays a d y n a m i c range o f a p p r o x i m a t e l y 110 d B . It is divided i n t o decades.
These callouts are n o t meant to be exact b u t are o n l y a p p r o x i m a t e . T h e y ' r e given f o r relative dis
cernment o f signal s t r e n g t h .
M o d u l a t i o n (or carrier deviation) is displayed b y t h e instantaneous h o r i z o n t a l expansion and
c o n t r a c t i o n o f the trace w h e n t u n e d at the upper center. L o u d passages are indicated b y w i d e
traces, w h i l e softer passages are seen as p r o p o r t i o n a l l y shorter traces. O v e r - m o d u l a t i o n by the trans
m i t t e r is displayed as an excessively w i d e trace e x t e n d i n g b e y o n d the t w o vertical lines o n either
side o f the center line. These vertical lines represent the instantaneous peak deviation o f 7 5 k H z
either side o f the center line.
Weak distant stations can be seen o n the scope a l t h o u g h they may be below the tuner's set
m u t i n g threshold. A d j u s t i n g antenna d i r e c t i o n w i l l f r e q u e n t l y increase signal strength s u f f i c i e n t l y t o
pull the signal o u t o f the inter-station noise level and give g o o d r e c e p t i o n . I n e x t r e m e cases, a very
weak signal can be made audible b y setting M u t i n g t o O f f .
A s t a t i o n broadcasting an SCA sideband can also be seen w i t h the T u n i n g Display. It is
detected b y an inward reach o f the trace w h e n the trace is a t the upper p o r t i o n o f either side o f the
trace p a t t e r n .
Adjusting Antenna Direction For Minimum Multipath — The t u n i n g display serves the im
p o r t a n t f u n c t i o n b y showing w h e n the antenna is p o i n t e d t o best possible d i r e c t i o n to m i n i m i z e
m u l t i p a t h . M u l t i p a t h interference, similar t o a " g h o s t " in T V pictures, produces d i s t o r t i o n in the
F M signals a t t h e receiving antenna. T h i s results in a d i s t o r t e d sound. T o m i n i m i z e m u l t i p a t h inter
ference, and o b t a i n the best reception f r o m each s t a t i o n , adjust the antenna t o the d i r e c t i o n w h i c h
results in the smoothest and most h o r i z o n t a l trace. T h i s d i r e c t i o n f r e q u e n t l y m a y n o t be the same
as the d i r e c t i o n for the strongest signal ( m a x i m u m vertical d e f l e c t i o n ) .
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