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Entries in Communication (2)

Wednesday
Mar022016

Is GoTenna Ready for SAR?

After many months of waiting, I was finally able to get my hands on a pair of GoTenna devices to field test. These devices are VHF radio transceivers that pair via Bluetooth that enable two phones to pass text messages without requiring any cell service. The required phone app allows for text messages, pinging connectivity between devices, and the swapping of location using the phone's onboard GPS to fix position. There are also downloadable base maps to display position data.

 The pairing process was quick and easy with the Android phones used in the test, and the software and hardware performed without any difficulty. The interface is similar to most of the available messaging apps. Although, only text can be sent, so there is no photo sharing or other file sending available. 

While testing one person attached the device to his pack according to the suggestion of the manufacturer, and the other person placed it in his pocket and started off on his mountain bike. We communicated via 5 W VHF radios with rubber duck antennas to compare the coverage. Obviously, as long as the GoTenna was in the bike rider's pocket, the connection was severly compromised. Periodically the rider would stop, remove the device, and attempt to communicate. This was done until we could no longer maintain a reliable connection. As expected, the most reliable communication came with optimized antenna location. If both ends of the communication held their devices high, and vertically polarized, the likelihood of a reliable connection increased. 

In the environment tested (shown on the map to the right) the furthest that we could maintain a connection was approximately 0.6 mi. This was challenging RF terrain, however. The blue shading on the map is a line of site layer, so we were able to maintain some modicum of communication outside of this region. By comparison, the 5W VHF radio allowed reliable communication greater than 1 mile in this same terrain.

We were operating in the MURS band with the voice radios. A bit of testing shows that the GoTenna may be operating on MURS channel 1 (151.82 MHz), so we avoided this channel, and used MURS channel 5 (154.60). We noticed that if you were transmitting with the 5W radio on channel 5, it would interfere with the GoTenna messages. This may be something to consider since much of our SAR work is in the neighborhood of this portion of the spectrum. 

Given the additional overhead of having to pair a smartphone to the device, and the limited range, the GoTenna doesn't seem to provide any significant communications advantage over, or in addition to, the typical portable radio. Still, this is the first generation of such a device, and for those of us who are attracted to all things RF, it is most intriguing.

Wednesday
Jul242013

Smartphones and the SAR Mission, Part IV: Communication

Good communication is key to a successful SAR mission and team administration. As SAR team members we are used to getting calls in the middle of the night, and making last-minute plans. It is the way things go in the SAR world. For effective, timely communication we must use multiple channels. These are often email, pager/SMS messages, phone, and radio. Traditionally radios have been the sole source of communication in the field, but with the increased cell coverage in many areas, the cell phone is becoming a useful tool for tactical communication as well. 

I have often wanted to set up a group text messaging system for a single event that didn't require a bunch of configuration ahead of time. I wanted to be able to put everybody at an incident on the same "channel" regardless of the type of phone that they use. This would provide an additional level of privacy as well as an additional communications channel that is easy to use. This is different from a callout system. I've searched for something that I can quickly deploy on scene with minimal set-up and management: an ad hoc messaging system that works across agencies and phone types.

Group Messaging

There are a host of tools designed for groups to stay in touch, and a number of them could be handy in the SAR world as well. For SAR applications, I prefer that there be SMS functionality. SMS does not require a data connection, and any phone can participate, so it lends itself to the heterogeneous phone landscape of the SAR world. One such tool that I have used with some success is GroupMe. Groups can be created on the fly via SMS, smartphone app or via the web, and participants can send messages via the app or SMS. Photos and your location can also be sent, but only through the smartphone app. The smartphone app is available for iOS, Android, Blackberry, and Windows Phone. 

My experience with GroupMe, however, is that it works best for small groups. There is no way to limit the traffic. Every subscriber sees every message, so it can be very noisy with larger groups. Also, there is no way to direct message a single person without the app; direct messages do not work via SMS. Subscribing to a group requires an invite. This is good for security, but not useful in a SAR scenario when the command post is trying to quickly get people into the field. It is much easier to have the sign-up be user-initiated. GroupMe is a cool tool that may work well for your team. My experience is that with more than 5 or 6 people, the group becomes rather "noisy", so I have abandoned it for SAR use.

A few months ago, while researching for my "day job", I came across a tool that I immediately recognized as being handy for SAR missions. The tool is called Celly, and it does exactly what I have been looking for.

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