Comtech EF Data DST User Manual
Page 62
Digital Satellite Terminal System
Revision 1
Operation
MN/DST.IOM
A–4
The Ku-Band error budget with the 3 ppm LNB was presented earlier, and the budget for
an externally referenced LNB at 0.02 ppm follows:
± 309 Hz
BUC with LO = 15,450 MHz,
±0.02 ppm
± 215 Hz
LNB with LO = 10,750 MHz,
±0.02 ppm
± 58 Hz
Modulator + Demodulator at 1,450 MHz,
±0.02 ppm
± 10,000 Hz
Satellite Uncertainty
± 10,582 Hz
± Uncertainty
x 2
Convert
± to total End to End
21,164 Hz
End to End Uncertainty fv
÷ 2.6
2 * k, where k = 1.3
8,140
sps
SR
≥ fv /(2 * 1.3), minimum symbol rate for 1.3 carrier spacing
The highest stability and least amount of frequency uncertainty is provided when an
externally referenced LNB (and BUC) is connected to a modem with a
±0.02 ppm
reference.
Figure A-2. Minimum Symbol Rate versus Satellite Uncertainty for Ku-Band and C-Band
Minimum Symbol Rate (vs) Satellite Uncertainty
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
20
25
30
Satellite Uncertainty (+/- kHz)
Mi
n
imu
m
S
y
mb
o
l R
a
te
(
k
s
p
s
)
BUC = +/- 0.02 ppm, Modem +/- 0.02 ppm
Ku-Band
LNB = +/- 3 ppm
C-Band
LNB = +/- 3 ppm
Ku-Band or C-Band
LNB = +/- 0.02 ppm