Televes 233306, 233311, User Manual

Page: 16 / 24

Optical Fiber Transmitter and Receiver
16
the row of 8 dB of loss calculated for the optical
fiber link in the value of 0.6 dB, which would
correspond EINn =-139.9 dB/Hz.
Apply the formula [1] and we obtain:
EIN
TV
= -139.9 + 10×log(5×10
6
)= -72.9 dBm
Now apply the formula [2] to calculate the C/N, as
follows:
C/N
TV
=Vin - EIN
TV
C/N
TV
= -26 dBm -(- 72.9 dBm) = -26+72.9
Then, C/N
TV
= 46.9 dB
In practice, combining satellite and off-air/CATV
channels makes the off air/CATV C/N 1dB worse.
Example 1
Calculate the C/N at the output of the optical
receiver (C/N link), in the installation of the figure
below:
This is a link where the optical signal is split
between 4 fibers of 0.62 miles ( 1Km ), using a
splitter ref. 2339. The signal received at the other
end is converted back to RF using of the optical
receiver ref. 233501.
The transmitter input levels:
- 23 dBmV (-26 dBm 42CH CENELEC) analog
channels, off-air/CATV band.
- 13 dBmV (-36 dBm)
digital channels,
off-air/
CATV+SAT.
Analog terrestrial channel bandwidth: 5 MHz
Satellite digital transponder bandwidth: 27 MHz
On the other hand:
• 0.62 miles (
1Km ) optical fiber is equivalent to 0.4
dB of attenuation.
• The splitter features 6.8 dB loss.
• The 2 fiber optic connectors represent 0.8 dB (2
× 0.4).
Therefore, total losses of the optical fiber link are:
FO Optical splitter Connectors losses
This is:
0.4 + 6.8 + 0.8 = 8 dB
Now we use the formulas and data given in the
table above.
For the off-air/CATV band, we consider the column
of the Gain at 807 MHz. This column intersects with
INPUT signal
off-air/
CATV+SAT
RF signal
off-air/
CATV+SAT
0.62 miles
(1 Km)
RF signal
off-air/
CATV+SAT
RF signal
off-air/
CATV+SAT
RF signal
off-air/
CATV+SAT
(1)
(2)
(4)
(3)