tcrabtree
lvl.1
United States
Offline
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I'm the president of Eureka Technology, we make the Marco Polo Tracking and Recovery System so I can't claim a totally unbiased answer to your question. But here goes..
As you know, GPS is principally a self location system - a GPS receiver allows you to know where YOU are. To use GPS as an object location system there must be a back channel to get the GPS coordinates of the object back to the searcher. Typically this is done through a cellular SMS path as that leverages the cellular network and the investment you have already made in your GPS enabled smart phone. This is great providing that there is strong cell coverage in the area you fly, or more importantly, in every spot that you might unintentionally land. Keep in mind that when you are using your cell phone you are holding it 6 feet of the ground and, when necessary, orienting yourself to get the best signal. Crashed aircraft don't do that! If you land upside down in a ditch then the cellular transceiver better work where it is, as it is, or it isn't going to do you much good.
A cellular back channel isn't the only method that is used for GPS-based object location. In the pet tracking world there are products such as the Garmin Astro, Sport Dog Tek and Roameo that use an RF back channel to a GPS equipped receiver. These products are quite heavy (6-8 oz.) and have a battery life that is typically shorter than one day so they are not of much use for drone tracking.
That brings us to self-contained radio direction finders. The familiar wildlife tracker uses a RF beacon transmitter and a directional antenna connected to a very narrow-band RF receiver. These systems can have excellent range but suffer when you are up close to the object because the receiver becomes overloaded with signal and the signal can bypass the directional antenna. This makes getting exactly to the location of the object very difficult. Also, although the transmitter is very simple and generally just transmits a short burst of RF once a second, the tight frequency tolerance requirement of the transmitter and receiver drive up the costs and these systems, when complete with Rx, Tx and antenna typically run $600-$800.
The two economical alternatives to traditional radio direction finders are Loc8tor and Marco Polo. Loc8tor uses 2.4 GHz, essentially a Wi-Fi transmitter and receiver. The handheld search unit has an internal, directional "patch" antenna that allows you to sweep the receiver around and find the direction producing the strongest signal. The strengths of the Loc8tor system include small size and low cost, the major weakness is limited range. In ideal conditions the range is about 600 feet and any obstructions such as a rock, tree or dense foliage reduce that substantially. 100-200 feet of actual usable range is not unusual.
Marco Polo is different, Marco Polo uses pseudo-Doppler automatic direction finding which has two advantages. First, you don't sweep an antenna and interpret the signals, the system does that for you and displays the bearing on an LCD display in the handheld locator. Secondly, since Doppler is a phase-based system rather than amplitude-based, it works to within 1-inch of the object. Imagine searching for a drone in, say, a cornfield where you practically have to step on it to find it. With Marco Polo you WILL step on it if you don't watch where you are going.
Marco Polo uses microprocessor-controlled transceivers to be placed in the object to be tracked. The 12-gram transceiver only transmits when accessed by the locator so when flying there is no RF being transmitted at all, you are in total control of that from the ground so there is no possibility of interference with any of your other radio equipment. When activated the transceiver broadcasts a full 250mW of power vs only 10mW for most other direction finder systems. This combined with the sensitive (-125dBm) narrow-band FM receiver in the locator gives a line-of-sight range of up to 2 miles. And because the transceiver is not continually transmitting when not being tracked the rechargeable LiPo battery lasts for 10 days in standby.
You can read more about the Marco Polo system and see all the specifications at FindMyLostDrone.com. |
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