GE MDS iNET 900, Справочное руководство

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132 iNET Series Reference Manual 05-2806A01, Rev. J
At Remote Gateway sites and units in point-to-point LANs, a directional
Yagi (Figure 4-6) antenna is generally recommended to minimize inter-
ference to and from other users. Antennas are available from a number
of manufacturers.
Invisible place holder
Figure 4-6. Typical Yagi Antenna (mounted to mast)
Feedlines
The choice of feedline used with the antenna should be carefully consid-
ered. Poor-quality coaxial cables should be avoided, as they will
degrade system performance for both transmission and reception. The
cable should be kept as short as possible to minimize signal loss.
For cable runs of less than 20 feet (6 meters), or for short range trans-
mission, an inexpensive type such as Type RG-8A/U may be acceptable.
Otherwise, we recommend using a low-loss cable type suited for
900 MHz, such as Heliax
® .
Table 4-1 lists several types of popular feedlines and indicates the signal
losses (in dB) that result when using various lengths of cable at
900 MHz. The choice of cable will depend on the required length, cost
considerations, and the amount of signal loss that can be tolerated.
The tables below outline the minimum lengths of RG-214 coaxial cable
that must be used with common GE MDS omnidirectional antennas in
Table 4-1. Length vs. Loss in Coaxial Cables at 900 MHz
Cable Type
10 Feet
(3.05 m) 50 Feet
(15.24 m) 100 Feet
(30.48 m) 500 Feet
(152.4 m)
RG-214 .76 dB 3.8 dB 7.6 dB Unacceptable
Loss
LMR-400 0.39 dB 1.95 dB 3.90 dB Unacceptable
Loss
1/2 inch HELIAX 0.23 dB 1.15 dB 2.29 dB 11.45 dB
7/8 inch HELIAX 0.13 dB 0.64 dB 1.28 dB 6.40 dB
1-1/4 inch HELIAX 0.10 dB 0.48 dB 0.95 dB 4.75 dB
1-5/8 inch HELIAX 0.08 dB 0.40 dB 0.80 dB 4.00 dB