On the Memorial

Entries in radio (2)


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.


Retractable Outdoor Products

This is a short discussion about some retractable products I have used for recreation and search and rescue. I do a lot of canyoneering which often involves swimming through hydraulics or jumping off rocks up to 13 meters above the water. I have lost many knives and a couple carabiners to this turbulence. For search and rescue I hike a lot as well as hang out on the side of rocks or in caves. Over the years gear has disappeared in these environments as well. I have been using a small retractable gear tether for a few years made by Key-Bak ( I use it to attach my whistle to my helmet. It has functioned well through many swims.

Over the past year I have housed my point and shoot waterproof camera in a T-Reign ProCase. ( It has been great. There is a retractable cord that attaches to the camera. With one hand I can pull the camera out, activate it, take pictures and return it to the case. It is easy to detach the camera and hand it to someone else to use. The case is quite durable. A few years ago 4 members of the Cave Team tested some prototypes. They got a bit carried away, even backing a car over a case! The cases survived the assault. I can attach the case to my back pack shoulder strap or improvise a strap to wear over my shoulder. It can also be worn on a belt. The case handles the abuse of search and rescue, climbing, mountaineering and swimming. 

Recently I obtained the ProHolster. This is very similar to the ProCase but without a lid. Instead it has a strap. The small case fits my submersible WX370S radio perfectly. It is my primary SAR radio. It too has an easily detachable retractable strap. It has the same attachment system as the ProCase. Hence I can wear my radio in a variety of ways:  pack strap, over my shoulder, on my belt. Over the years I have witnessed many SAR radios lost. This case should solve that problem. The video presents the product well. The attached picture shows my radio and the holster.