User's Manual

MDS 05-3301A01, Rev. C MDS 9810 Installation and Operation Guide 23

Antennas

Two antennas are required at repeater stations—one for each radio.

Measures must be taken to minimize the chance of interference between

these antennas. One effective technique for limiting interference is to

employ vertical separation. In this arrangement, one antenna is

mounted directly over the other, separated by at least 10 feet (3 Meters).

This takes advantage of the minimal radiation exhibited by most

antennas directly above and below their driven elements.

Another interference reduction technique is to cross-polarize the

repeater antennas. If one antenna is mounted in the vertical plane, and

the other in the horizontal plane, an additional 20 dB of attenuation can

be achieved. (Remember that the corresponding stations must use the

same antenna orientation when cross-polarization is used.)

System Addresses

The two radios that are wired together at the repeater site must have dif-

ferent system addresses. To set or view the system address, see “ADDR

[1...65000]” on page 36.

Interface Wiring

A null-modem cable (Figure 19) is required between the

DATA INTER-

FACE connectors of the two radios forming a repeater station. This

allows them to freely exchange data even though they are both config-

ured as DCE devices.

Invisible place holder

Figure 19. Data Interface Cable Wiring for Null-Modem Cable

(used for traditional repeater)

Diagnostic Limitations

As of the date of publication, over-the-air diagnostics is not fully sup-

ported in repeater systems. Diagnostic data from these systems may be

unavailable or unreliable. This is particularly true if a repeater radio is

configured as the “root” in a diagnostics scheme (See “Performing Net-

work-Wide Remote Diagnostics” on Page 53.) Better success might be

achieved by picking a standard remote to use as the root.

DB-25 DB-25

Spread Spectrum

Master

(DCE)

Spread Spectrum

Remote

(DCE)

TXD

RXD

GND

RXD

TXD

GND