TELE-audiovision - The World’s Largest Digital TV Trade Magazine - page 53

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1 -12/2013 —
TELE-audiovision International —
全球发行量最大的数字电视杂志
Ka-Band Satellite Scan
56. This waterfall diagram shows the horizon from about 30.0E to
30.0W using the Inverto Ka LNB. Only 9.0E is broadcasting transpon-
ders in the 19.7 GHz – 20.2 GHz range.
57. This picture shows 9.0E over a period of time (about 30 seconds).
The second half (lower part – representing about 15 seconds) of the
waterfall diagram was recorded during a sporadic rain shower. Curi-
ously the rain did not produce any signal loss.
What does 1.2E-03
mean? BER stands for Bit
Error Ratio: the measu-
ring instrument will basi-
cally count the erroneous
bits within all received
bits and calculate this
simple formula:
Because the amount
of erroneous bits is nor-
mally very small, let’s
say 1 wrong bit in every
1.000.000 bits, it would
look odd to see a va-
lue of 0.000001 on the
meter’s screen. A much
more convenient format
would be 1x10-6. Cal-
culators will frequently
show this number as 1E-
6, instead, to save some
screen space. So this is
what a reading of CBER =
1.2E-03 means: you will
get one wrong bit in eve-
ry 1200 bits received.
Let’s do the math:
CBER means that no er-
ror correction has been
applied to the signal, so
let’s now see what LBER
< 1.0E-8 means:
It means that after ap-
plying the error correc-
tion, we only will receive
one bad bit every hund-
red million received bits.
We will have a great pic-
ture without any notice-
able artifacts. However,
because our initial CBER
value is low, there is no
bad weather reserve.
If the signals gets only
slightly worse, the er-
ror correction will not be
able to correct the inco-
ming stream and picture
artifacts will be produ-
ced.
The thumb rule is: the
smaller the BER value
before error correction,
the better. Notice that
smaller means a bigger
number after the “E”, be-
cause there is a “-“ sign:
-5 is smaller than -3! The
smaller the number, the
more bad weather reser-
ve you will get. The BER
value after the error cor-
rection will give you an
idea, if artifacts will be
noticeable on the screen
with the current signal.
How to interpret BER
measurements
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