UHF Coverage Survey for Greenhithe Emergency Resilience Group
17 July 2021
Background
Greenhithe is a community of about 3000 households located on the Eastern side of the upper Waitemata Harbour, Auckland. There are two road access routes to the suburb, one from the North Shore in the East via Upper Harbour Highway, and the other from Hobsonville in the West via State highway 18 and the Upper Harbour Bridge.
The Greenhithe Emergency Resilience Group is made up of leaders from the local Fire and Emergency Service, Community Trust, Residents Association and Primary School.
As part of AREC support for the emergency preparedness activities of local community resilience groups North Shore AREC conducted a radio coverage survey of the Greenhithe area. The objective was to establish if UHF handheld radios would provide reliable communication between the local community hall where the Greenhithe Emergency Resilience Group would establish their base in the event of a disaster or other emergency, and the Neighbourhood Watch street contacts and other volunteers throughout the entire suburb of Greenhithe.
A computer generated UHF coverage prediction was completed Radiomobile Online application. The predictions assumed 1 watt and 5 watt handheld radios at each end of the path. This suggested that coverage would be adequate with the exception of a few low signal areas.
In order to validate the predictions it was decided to conduct field testing of the area to compare the computer simulation with real world observations.
The operation
On the morning of Saturday 17 July, eleven members of North Shore AREC traveled to Greenhithe equipped with AREC 477 MHz PRS radios and 2 metre amateur equipment to run some tests.
A base was set up at the Community Hall equipped with a 5-watt PRS base station and a 2 metre VHF radio operating on the Waitakere 146.70 MHz repeater for coordination and backup. The base station PRS radio used a whip antenna within the building to provide a worst-case scenario for the test.
Handheld radios used in the field were Motorola GP328 units with a nominal output of 4 watts. The base station was a Tait TM8115 with 5-watts output.
AREC members formed 4 mobile teams each with a driver and navigator/operator and spread out around the area to test comms.
A total of 88 points were chosen throughout the Greenhithe area, and each team was allocated their own list of points to test.
At each designated point, the teams contacted base and exchanged reports specifying the signal quality in each direction.
Signal reports at each location were tabulated and subsequently compared with the computer predictions.
Results
Two coverage predictions were created using the Radiomobile Online application
One for a transmitter power of 1 watt and one for 5 watts, both with antenna heights of 1.5 meters above ground and assuming zero gain antennas.
1 Watt coverage prediction
5 Watt coverage prediction
The actual results of the field survey fell somewhere between the two predictions, with some dead spots observed in areas predicted by the 1-watt predictions. There was a good correlation between observed and predicted signal levels.
The equipment used did not appear to provide as good coverage as predicted for 5 watts, but better than predicted for 1 watt.
Factors that may account for the discrepancy are that the radios and antennas used at both ends of the path were located in either vehicles or a building, and not in free space as assumed by the software.
Two main areas of poor coverage were identified.
Following the operation, a further prediction was completed assuming a base station antenna mounted at 8 metres above ground at the hall
This prediction suggests that a pole-mounted external antenna at the base would provide adequate coverage into all areas, including the observed dead spots, and allow acceptable comms throughout the Greenhithe area.
Coverage prediction for 8 metre high base antenna
Conclusion.
The Radiomobile application seems to provide adequate predictions as long as conservative power levels are assumed when setting up the software.
AREC is in discussion with a number of local community resilience groups in Auckland to provide support with their communication needs. Having validated the Radiomobile software predictions we are now more confident in using this application for comms planning in other areas.
In addition, the practical survey provided a great training opportunity for some of our newer members to get to grips with field operations, setting up a base, and use of AREC procedures.
Anyway – a great way to spend a wet Saturday morning. Many thanks to all who participated.