Feedlines; How Much Output Power Can Be Used - Microwave Data Systems iNet 900 Quick Start Manual

MDS 05-2873A01, Rev. A
DRAFT 6—8/29/01

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 RG8A/U may be acceptable.
Otherwise, we recommend using a low-loss cable type suited for 900
MHz, such as Heliax ®
Table 3 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 3. Length vs. loss in coaxial cables at 900 MHz
10 Feet
Cable Type (3.05
Meters)
RG-8A/U 0.85 dB
1/2 inch HELIAX 0.23 dB
7/8 inch HELIAX 0.13 dB
1-1/4 inch HELIAX 0.10 dB
1-5/8 inch HELIAX 0.08 dB

3.5 How Much Output Power Can be Used?

The transceiver is normally supplied from the factory set for a nominal
+30 dBm (1 Watt) RF power output setting; this is the maximum trans-
mitter output power allowed under FCC rules. The power must be
decreased from this level if the antenna system gain exceeds 6 dBi. The
allowable level is dependent on the antenna gain, feedline loss, and the
transmitter output power setting. Power considerations for point-to-mul-
tipoint and point-to-point systems using the iNet 900 transceivers are
discussed in the next sections.
NOTE: In some countries, the maximum allowable RF output may be
limited to less than 1 watt (For example, 100 mW /+20 dBm).
Be sure to check for and comply with the requirements for
your area.
MDS iNet 900 Installation and Operation Guide
.
50 Feet
(15.24
Meters)
4.27 dB
1.15 dB
0.64 dB
0.48 dB
0.40 dB
100 Feet 500 Feet
(30.48 (152.4
Meters) Meters)
8.54 dB 42.70 dB
2.29 dB 11.45 dB
1.28 dB 6.40 dB
0.95 dB 4.75 dB
0.80 dB 4.00 dB
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