Campbell Scientific LoggerNet Datalogger Support Software - Manual (Page 473)

Section 14. Troubleshooting Guide
If the VSWR is below 1.5:1, then power transmission is good. However, be
sure the antenna is oriented properly.
While at the station, check the voltage on the 12 V port of the datalogger both
with and without the radio transmitting. Regardless of the battery type, the
datalogger requires a minimum of 9.6 Volts.
14.6.3 Troubleshooting with Attenuation Pads
This test is used to measure the signal strength of the radio signal between two
radios. There are situations where the signal from one radio can be heard by
the other, but the signal is not strong enough to establish communications. In
general a signal strength of greater than –95 dBm must be maintained for good
communications.
There are many factors than can contribute to inadequate power in an RF
system.
• Line of sight may be marginal or poor.
• Vegetation on trees or other obstacles.
• Corroded connectors or connections not made properly.
• Inadequate antenna gain.
• Improper antenna alignment.
• Outside interference on the channel frequency from another source.
Testing the radio transmission quality between radios requires the use of a
programmable scanner and a set of attenuators or attenuation pads. You will
need someone at each end of the radio link with a way to talk to each other.
If the carrier detect light is coming on at the RF base station radio, but
communication quality is poor or not being set up properly, there may be a
marginal or low signal power inherent in the RF link. In this case, it is a good
idea to do a signal power check with attenuation pads for each sub-link in a
complete RF link. Every RF link has one or more sub-links. For example, if
there is one repeater in an RF link then there is a sub-link between the base
station and the repeater and a sub-link between the repeater and the field
station. The sub-links should be checked in both directions of communication.
Before proceeding, it is a good idea to calculate the theoretical signal power for
each of the RF links. Appendix C of Campbell Scientific’s RF Telemetry
manual outlines the calculations.
For proper radio communications the signal power must be greater than –95
dBm at the standard transmission rate. However, a signal can be detected on
the radios with a power greater than –115 dBm. Therefore, there is a 20 dBm
range in which the radios are not working, but may “sound” proper.
An attenuation pad inserted into the link increases the power loss of the system.
If a 20 dB attenuation pad, or two 10dB pads in series, are inserted into the link
and subsequently the radio will not detect the signal, the signal power is
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