Limitless™ WPMM Series
Issue 2
50051864
Honeywell Sensing and Control 29
7.4
Choosing an Antenna Gain (dBi) with Acceptable Fade-Margin
There are several different antenna gain options in the Limitless™ Series to choose from. This section helps
determine the antenna version(s) that will provide suitable RF signal performance for specific applications.
The Limitless™ Series antenna’s actual gain is measured by how much of the input power from the internal radio of
the WPMM monitor is concentrated in a particular direction. The WPMM monitor’s antenna transmits RF signals,
and also receives RF signals from a Limitless™ switch. In a particular application, transmit signal strength may be
better than the receive signal strength or vice versa. The intent is to choose an antenna with the optimum gain
relative to application conditions for both transmitting and receiving.
Fade-margin is the amount of excess power available above and beyond what is necessary to maintain a reliable
RF signal between the transmitter and receiver. Normally, an acceptable threshold of excess power to ensure
effective operation in a variety of environmental conditions is 10 dB. A simple way to determine if the signal strength
is sufficient is to temporarily install a 10 dB attenuator* between the RP-SMA plug of the antenna or remote cable
and RP-SMA jack of the WPMM monitor. This should be completed in an operating application environment with
good nominal environmental conditions. Starting with the antenna chosen in Section 8.2, install the attenuator and
operate the system until exposure of all normal application conditions is completed while monitoring the amber LED
(RF link/signal indicator of the WPMM monitor). If the fade-margin is unacceptable, the LED turns on solid indicating
that the antenna position on the Limitless™ switch and/or WPMM monitor will need to be changed or another
antenna type should be chosen.
Try several mounting locations and/or antennas while retesting each with the attenuator to determine the optimal
set-up that provides an acceptable fade-margin. Remember to remove the attenuator after testing is completed.
*Suggested sources/part numbers
•
10 dB attenuator (i.e. Crystek – Part number: CATTEN-0100)
•
RP-SMA female to SMA male connector adaptor (i.e. Connector City – Part number : ADP-SMAM-RPSF)
•
RP-SMA male to SMA female connector adaptor (i.e. Connector City – Part number : ADP-RPSM-SMAF)
