Microwave Data Systems MDS entraNET 900, System Manual

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MDS 05-4055A01, Rev. A MDS entraNET 900 System Guide (Preliminary) 107
Invisible place holder
Figure 5-5. 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 5-1 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.
Table 5-1. 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)
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