Multitech MT-SMI-DK, Development Manual

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CHAPTER 8 – ANTENNAS, CABLES, AND GPS
59 Universal Socket Developer Guide
Antenna diversity provides an advantage in complex environments because if one receive antenna has a poor
signal due to an interference null pattern, the other antenna is likely not in the null and will have better reception.
The radio compares the reception from both receive antennas and uses the one with the strongest signal.
Antenna diversity is unnecessary when the device has an unobstructed signal path from the cell tower, such as in a
flat area away from buildings. In good reception environments, the product application might prohibit using two
receive antennas.
Using Antenna Diversity
Antenna diversity can be turned on and off with an AT command. When antenna diversity is on and a like or
similar antenna is installed on both radio connectors, the radio automatically chooses the antenna with the best
reception. Consult the AT Command Reference Guide for your device for the AT Command you should use to set
diversity.
Placing External Antennas
Antennas are usually a quarter wavelength apart from each other. With multiband radios where the quarter
wavelengths in each band are diverse from each other, this rule may not be practical. Choose spacing based on
the band used most often or the band with connection difficulty. Some environments are harsher on particular
bands. Multi-Tech products have antenna connectors at the best spacing for the product size.
Placing antennas in close proximity to each other is not optimal, but you can do it if necessary. It depends on the
signal strength to and from each antenna.
Placing GPS Antennas
GPS antennas need a clear view of the sky. Position the GPS antenna so the diversity antennas do not block its
view of the sky.
Selecting Antennas
Antenna choice should be optimized for the product and application. Typically, both diversity antennas are the
same because either could be the main receive antenna. However, if the antenna connectors are too close
together, use a similar antenna on a short cable for the second receive only antenna.
Antenna Approvals and Safety Considerations
Note the following:

PTCRB and the carriers conduct antenna diversity tests.

There are no EMC concerns about antenna diversity.

All antennas need to have a minimum flammability rating.

Safety requirements depend on your final product.

Antennas are not approved for outdoor use. Customers should not extend antennas outside of the building.
Diversity and Power Draw
There are no significant power draw differences.