A.I.R. GMRS Repeater

Communication is a vital component with any disaster organization during deployments.  It is important that all volunteers of Anemoi Incident Response have the tools and technology to assist in the task at hand of helping communities and residents when disasters strike.   Most times communication links are cut off and the need for communicating information is difficult.   Part of communication technology is being able to communicate without cellular service.  The Anemoi Incident Response Auxcomm Team is committed to bringing new and old technology to solve a common problem during disasters. 

The Auxcomm Team has secured the use of a GMRS repeater system that will aid our volunteers to communicate during search and rescue operations, general ground operations, supply operations, and general base camp operations.

On May 25, 2023, the system was activated and put through a series of tests to find the limitations of the system.   This report will detail the tests results and conclusion of using a GMRS Repeater.

 Equipment:

Anemoi Incident Response GMRS Repeater

The repeater consists of two Motorola Radios 1225S used and refurbished UHF radios.  One for transmit and one for receive.  The radios are connected to a duplexer so that only one antenna is necessary.   The system also has a new power supply and a connector for battery operation.   The entire system weighs 9lbs and mounted in a small toolbox.  The output power is set at 35 watts and has 2 repeater frequencies.

The antenna is a GMRS Antenna is rated at 200watts, approximately 4 feet long with a 3dbi gain.

Components Test

Once all the connections were complete, the repeater was powered on.   No issues were reported during this phase, switching to each channel was easy, however, both the transmit and receive radios need to be switched to their respective frequency.

This test passed and no failures.

Distance Test and Results

These tests were completed to determine the maximum range of the repeater using different heights of the antenna and coax.   Also, these tests provided the maximum range when using an HT Radio versus a Mobile Radio.

Note:  This test was completed in Illinois in a heavily populated area.   Also, the terrain was a mix of trees, ridges, and dips, which affected the outcome and conclusion.   Weather did not have any affect on the results, however, it can.

Test #1

Antenna Height 18 feet, 75 feet of RG8X Coax.

          Distance HT 2 miles

        Distance Mobile 3 Miles

Test #2

Antenna Height 18 feet, 25 feet of RG8X Coax

          Distance HT 3 miles

          Distance Mobile 4 miles

Test #3

Antenna Height 24 Feet, 50 feet of RG8 Coax

          Distance HT 3-3.5 miles

          Distance Mobile 4-6 miles

After the three tests were completed, the results were mixed based on conditions, terrain, and equipment.   As noted, the terrain where the test was completed had interference of trees, dips, and ridges.   At worse during the test when in a dip, this resulted in no communication, the ridges provided great communication to no communication after passing a ridge, the terrain ridge was blocking the signal.  The vast number of trees provided many instances of poor noise communication.

However, during flat areas, communication was perfect to very little noise interruption.   But the distance was compromised by the vast number of trees. 

Also, we must keep in mind that UHF is a shorter distance than VHF.   UHF can work through obstructions a little better than VHF, but not all the time.

Poor communications and lack of distance resulted from an antenna height of 18 feet and using RG8X coax.   RG8X coax also proved to provide a higher SWR of 1.8, which is not the best.   However, there was no output power loss using 75ft of this coax.

Switching to 25ft of RG8X coax, improved the distance and SWR reading of near perfect, also no output power loss.   Though the antenna was at 18ft, the distance only improved slightly.

Switching the antenna mast to 20 feet and using 50ft of RG8 coax proved to be the better of the three tests.   Again, given the terrain issues, the antenna was higher, no power loss, and SWR near perfect, more distance was achieved.

Conclusion

Though the goal was 10-15 miles using a repeater either at 18ft or 24ft, this was not achieved and was impossible to get this result.    This was concluded with the factors as already stated above.

These tests did fail the 10–15-mile goal.

Since the 10–15-mile goal failed, it was concluded while looking over the data, distance points, and terrain issues, the repeater did work flawlessly within a decent range.

It was also concluded to run another test in a different location with more wide-open friendlier terrain.   The next test will be in mid to late June 2023.

However, in the meantime, the repeater did the job it was supposed to do, accepted a signal, and repeat it.  

We need to keep in mind that this is a portable repeater and not a stationery, there is no 100-foot building or tower that the organization can build to give this system better coverage.  Being portable also means the ability to take down in the event of severe weather approaching a base camp or operation scene.   An antenna at 24-30 feet is fine, however guy wires may need to be in place due to windy conditions, 20+mph, 18ft no guy wires would be necessary for winds 20-25 mph.

Best solution

Building upon this system is the key.   During operational periods, these portable repeaters can be in place at the actual operational scene to provide communications.   A repeater, and antenna at 15-18 feet will provide enough coverage for 2-4 miles.    As teams are developed, they can be provided with a repeater, HT radios, mobile radios, and proper antennas.  

Also, operating a base camp that is within 4-5 miles of an operational scene will be adequate as well.

We also must remember that when setting up communications, the environment, terrain, and weather needs to be reviewed and how best to use these repeaters.    This repeater system will work, it is just a matter of how we use it during each deployment.   Because each deployment is different and terrain conditions are different, results will vary, it may work great in one deployment but may fail completely in another.

Final Word

I have mixed emotions about the outcome, I am happy that the system failed on some occasions but happy it did not on some others.    We need to know the limitations.  I personally would use these repeaters no matter what distance, as the clarity in the communication is much better than Simplex sometimes.   Also, these repeaters are the best way to build upon a communication system that can be used.

 Tom – KD9JSA

Anemoi Incident Response