RACOM Ray2, Руководство пользователя

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30 cm ... 32.2 dBi
60 cm ... 37.8 dBi
99 cm ... 42 dBi
Step 2 - Free space loss calculation
FSL = 32.44 + 20log f + 20log D = 32.44 + 20log17.2·10
3
+ 20log4 = 129.1 dB
Step 3a - Rain attenuation
For 99.99% availability in rain zone B the rain rate is R
0.01
=32 (see Fig. 2.1)
For f=17 GHz k
h
=0.06146; α
h
=1.0949; k
v
=0.06797; α
v
=1.0137
Vertical polarization:
γ
R0.01
= k
v
.R
α
v
0.01
= 0.07 · 32
1.01
= 2.32 dB/km => for 4km distance 9.3 dB
Horizontal polarization:
γ
R0.01
= k
h
.R
α
h
0.01
= 0.06 · 32
1.09
= 2.62 dB/km => for 4km distance 10.5 dB
Step 3b - Attenuation due to multipath propagation
We have to find required fade margin for reliability of the link 99.99 percent.
Path inclination:
The percentage of time that fade depth A (dB) is exceeded in the average worst month is calculated
as:
P
0
= Kd
3.4
(1+| ε
P
|)
-1.03
f
0.8
×10
0.00067h
L
-A/10
P
0
= 10
-4.6-0.0027×(-300)
× 4
3.4
(1+|6.25|)
-1.03
17.2
0.8
×10
0.032×10-0.00067 ×295 - A /10
P
0
= 0.022871 ×10
-0.19765 - A /10
For reliability 99.99% is P
0
=0.01 we get exponential function for A:
A = -0.19765 - 10log(0.01/0.022871) = 3.4 dB
The minimum fade margin required to suppress multipath fading on this link would be 4 dB.
Step 4 - Choice of Tx power and antennas
Step 5 - and Link budget calculation
Calculation in steps 3a and 3b determines the minimum fade margin required for stable link opera-
tion as 11 dB (rain attenuation is dominant). If you use the maximum performance of antenna with
diameter of 30 cm, complete the radio formula as follows:
P
R
= P
T
+ G
T
+ G
R
− FSL = 5 + 32.2 + 32.2 − 129.1 = −59.7 dB
Fade margin:
A = | P
S
| − | P
R
| = 79 − 59.7 = 19.3 dB
The resulting fade margin is larger than the required 11 dB. Current legislation in the Czech Republic
allows maximum EIRP of +20, i.e. the sum of transmit power and antenna gain at the transmitter
can be 20 dB at the most. For 99cm antennas, TX power can be up to 20 - 42 = -22 dB, the resultant
equation is as follows:
P
R
= P
T
+ G
T
+ G
R
− FSL = -22 + 42 + 42 − 129.1 = −67.1 dB
19 © RACOM s.r.o. – RAy2 Microwave Link
Implementation Notes