Sierra Wireless DART 200 CDPD Modem manual Antenna considerations

DART 200 CDPD Modem User’s Guide 2 Installation and Setup

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NOTE: Snub-nosed (rubber duck) antennas, although they may work in some areas, are NOT recommended.

Operating the unit without an antenna does not damage the modem but can cause unpredictable results.

CAUTION:

For outdoor fixed installations ground the antenna cable using an antenna discharge unit to prevent damage to the modem and the attached equipment.

Antenna considerations

The DART 200 uses standard mobile cellular radio signals and any standard cellular antenna of good quality with a maximum gain of 3 dB (FCC requirement) will function properly subject to the following guidelines:

∙Location

Locate the antenna as far away from personnel as possible to minimize signal blocking. For optimum reception, in fixed location applications position the antenna above the height of personnel and nearby equipment or structures. If used inside locate the antenna as close to a window as possible. In mobile applications, locate the antenna outside and away from or above any portion of the vehicle body that can block the RF signals. To determine the actual signal strength, attach a PC with an ASCII terminal emulator, such as Procomm, or Kermit, to view the Receive Signal Strength Indication (RSSI) value in S-Register 102.

∙Antenna cable

Select an antenna cable with a low loss, high quality, 50 ohm, coaxial cable with the appropriate connectors. The cable can be any length, but lengths greater than 12 feet increase cable loss and offset the antenna’s nominal gain. If longer length cables are required, use a heavier wire gauge to reduce the dB loss/ft and to minimize the effect of the cable loss on antenna gain.

∙Ground plane

For installations where a good antenna ground plane (metal surface) is not available, use a non-ground plane type of antenna to help maximize signal reception

∙Proximity to other antennas

In general, do not locate the DART 200 and its antenna closer than five feet to another antenna; in certain cases, even more separation is required. In many vehicular applications, there are high-power two-way voice transmitters used and usually the antenna mounting locations are not five feet apart. The effect of the interference from the two-way transmitters varies from slowing down response times to blocking modem transmission.

In this situation, separate the antennas as far as possible and then do a test with the voice system also being used. If the DART 200 works satisfactorily you do not have an interference problem. If it does not work properly, then use filtering on the two-way output, the DART 200 input, or both. The calculation to determine the required filtering is not trivial and usually requires an RF engineer. However, if you do not have the option to do a test first, this analytical approach is your only option.

PN1197-00 Revision 1.0 2-3