Optical Fiber Transmitter and Receiver
18
RETURN CHANNEL
For the return channel transmitter, the table of
attenuations, link gain and equivalent noise is:
Link attenuation
(dB)
Gain at 30 MHz
(dB)
EINn
(dBm/Hz)
0
23
-152.5
3
16.6
-149.5
4
14.6
-147.6
5
12.7
-145.7
6
10.7
-143.9
7
8.7
-141.9
8
6.7
-140
9
4.7
-138.1
10
2.6
-136
11
0.4
-133.4
12
-1.5
-132
13
-3.5
-130.5
14
-5.5
-128.5
Measurements made with a transmitter that delivers 2.9dBm
followed by an optical attenuator connected between the
transmitter and the optical receiver.
Use the formulas 1 and 2 for making calculations.
The calculation process is the same as in the case
of the forward channel.
EINn(SAT) = -125.4 dBm/Hz
G(2.1 GHz)= -16.3 dB
Therefore, the RF signal level delivered by the
receiver is:
Vout
rcvr
(dBmV) = Vin
xmtr
(dBmV) + G (dB)
This is:
V
out rcvr
TERR (dBmV) = 19 -17.3 = 1.7 dBmV
V
out rcvr
SAT (dBmV) = 19 -16.3 = 2.7 dBmV
Applying the formula [1]:
EIN
TV
= EINn(TV) + 10×log(8×10
6
) [dBm]
EIN
TV
= -122.8 + 69
EIN
TV
= -53.8 dBm
And by the formula [2] is obtained:
C/N
TV
= - 30 dBm - (- 53.8 dBm) =
23.8 dB en TV
Likewise, we calculate the C/N for SAT channels,
resulting in:
EIN
SAT
= - 51.1 dBm
C/N
SAT
= -30 - (-51.1) =
21.1 dB en SAT
If the resulting C/N is close to the threshold it
is advisable to increase the input levels to the
transmitter by one or two dB to ensure enough
margin before distortion.
Содержание 233306, 233311
Страница 2: ......
Страница 24: ...televes com...
