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If your RTU's are located where the associated antenna cannot visually see the SCADA master radio station's antenna then it is not clear if the radio signals will make the journey reliably. When the two radio stations antennas are within optical view of each other the radio path is are considered "Line Of Sight". When they are not they are referred to as "Path Critical". Path critical is not a matter to be taken lightly, as guessing incorrectly as to the RF signal quality can cause errors in cost estimations, taller antenna support structures, cost more, and potential delays in turn up time. It can also cost frustration with the contractors, and a sense that the engineer really did not know what they needed to know about this aspect of the project. It takes time to build a taller antenna support structure, especially when you created an initial structure that was too low, and now has to be removed.
If the SCADA radio network designer chooses to perform a "Radio Study" in effect they can enjoy a report that allows the end user to try the actual SCADA Radio Network design before they buy it so to say. The designed antenna heights will be tested to see if they facilitate a reliable (20 dB Fade Margin) communications. A radio study will place the actual SCADA Radio Network hardware specific out in the field. The actual Radio models will be used, it is often practical to use slightly smaller antennas when performing these Radio Studies the differences between as studied antennas and as built are negated with a math formula to compensate for any possible differences. The Master Radio Station and its associated antenna system located at the initially designed height, along with the RTU's sites to be studied. If a site has a measured low SCADA radio communications performance issue, the RTU's antenna height can be adjusted upwards and if necessary the master radio site can be adjusted upwards as well. The Radio Surveyors will travel to all of the RTU's sites of interest for this SCADA Radio Network and actually take field measurement with an actual RTU version of the SCADA Radio. Receiver signal strength (RSSI) along with Signal to Noise Radios and possibly "Data Error Rate" information as well will be documented. GPS coordinates along with Distance and Bearing data will be logged and valuable for future installation crews as this gives the installers a bearing to aim what is usually a directional antenna at each RTU. Photos of the test equipment being deployed can be useful for future reference.
I have attached a PDF copy of a report we performed recently in Cape Coral, Florida. It is representative in of a SCADA radio network radio study in many ways, yet different in a couple of ways too. This radio study was performed in the 900MHz multiple address system (MAS), MAS requires FCC licensing for operation. 900MHz RF signals can be highly unpredictable when non line of sight conditions exist as they did in Cape Coral. This radio study took advantage of the fact that there was an existing 300' tall antenna tower located at the water plants property that was available for use for this SCADA radio network. The SCADA designer, myself choose to locate the SCADA master's antenna at the 100' above ground level height on the tower. This was likely 25% higher than necessary, but there was no additional cost associated in using a tower that was already constructed and available to the city. Also this mounting location was unused antenna tower real estate, as the other antennas on the tower were located above the 100' height. The RF signal strengths to the RTU's measured were very strong due to the high placement of the master SCADA radio station's antenna. The farthest RTU's away from the master were ~ 3 miles. Click this link to read the radio study.
If your SCADA radio network master and associated RTU's are relatively close, with in about 1/2 mile and the antennas are able to see each other, then the need for a radio study is ambiguous. However if the antennas are not with in visual sight of each other, plan on a radio survey. A case in point was in Eustis Florida, I once performed a radio study there. The master radio had its antenna located atop a 100' plus tall water tank. It needed to communicate through a pine forest to an RTU less than a mile away. Zero signal was available until the RTU antenna cleared the 80' tall slash pine trees. The City abandoned their interest in 900 MHz spread spectrum for 450MHz licensed to mitigate this problem. The initial design would have failed miserably and caused cost overruns and delays that would have made both sides frustrated, if a radio study was not performed as part of the project. Learn from the mistakes of others, perform a radio study when in a path critical environment.
A radio study can save provide significant cost savings when it comes to antenna structure costs. It can be wasteful to use a 40' tall antenna tower when a 20' tall one will supply the necessary RF fade margin and cost 1/4 as much. Multiply this idea in a 50 or 100 RTU system and the cost savings can be compelling. Almost all SCADA radio network projects require the performance of a radio study.
If you have any questions on a specific project or an application you would like to discuss, please feel free to call on me, Mark Lavallee. I enjoy sharing my 30 years of experience and knowledge. My company is often used to sub consult with consultants, assist controls system integrators, and work with the end users directly.