SensorGnomes for your Motus receiving needs
What is a SensorGnome?
SensorGnomes are an open source automated VHF telemetry system primarily used to log detections of animals carrying VHF transmitters compatible with the Motus Wildlife Telemetry System. Specifically, a SensorGnome equipped with one or more compatible receivers can detect pulses from Lotek coded transmitters or Cellular Tracking Technology (CTT) coded transmitters.
Key Features of the SensorGnome for Automated VHF Telemetry:
Simultaneous scanning of multiple (up to 4) receivers (e.g., FUNcube Pro+, CTT Motus adapter)
Dual power source: 120V AC standard or, optionally, 9-36 V DC (e.g., solar)
Precise timekeeping (<1 microsecond accuracy via GPS sync)
Effectively unlimited storage, but 32GB standard
Stores a complete record of all 'detections' for later processing
Stores information on 'noise' and signal strength
Allows for multiple/alternate tag-detection algorithms
Uploads data directly to the Motus Wildlife Telemetry web-server if an internet connection is present
The SensorGnome is open source. Open source means reduced costs and flexibility in the choice of components. It means you can customize the SensorGnome to fit your needs. It also means that you have some decisions to make, and those decisions will affect the cost and performance of your SensorGnome. Here we discuss the major options available to customize your SensorGnome.
How many antennas/receivers?
How many antennas your receiving station needs depends on your objectives. A single omni-directional antenna may suffice to record presence/absence of, say, colonial roosting shorebirds. A "detection fence" arrangement of 2 opposing long-range Yagi antennas may be adequate to detect animals passing by during migration. A more complicated arrangement of antennas may be required to meet a combination of objectives. In a SensorGnome, each antenna gets a dedicated receiver. How many antennas you need dictates how many receivers you need.
If you want to add more antennas down the road, the SensorGnome can easily expand to up to 4 antennas by simply adding receivers. Beyond 4 antennas, there are a few components to tweak. But we can help you through that process!
With the number of receivers decided, the next choice is between receivers. The two available options, FUNcubes and compatible RTL-SDR receivers, trade off cost for performance. FUNcubes are considerably more expensive than a decent RTL-SDR, but they typically produce less noisy recordings. To put it simply, less noise means tag transmissions are easier to recover, which in turn means more detections and increased detection range. Unfortunately, there's no good answer to the question of "how much better" FUNcubes are for Motus-related purposes. We're working on some simple tests to help put some numbers to the comparison. We've used both receivers successfully, but our recommendation is to stick with FUNcubes if your budget can handle it.
AC or DC power source?
If you're confident you'll be locating your SensorGnome within a few feet of an AC power source (think of a standard wall outlet in your home), you can save $50 by not adding the the option for a DC power source. But you will need the components for a DC power source if powering your SensorGnome with solar or another DC supply (e.g., a 12V LED power supply). By the way, using a 12V power supply can be an attractive and cheaper alternative to solar when you have AC power nearby (within 500' or so) but not close enough to use the AC adapter for the Raspberry Pi. Ask us how!
What type of coaxial connector for your receivers?
Depending on your antenna source, you're likely going to be using coaxial cables with either PL-259/UHF-male connectors (e.g., Laird PLC-1669 9-element Yagi) or BNC-male connectors. If you need a different connector (e.g., N type), let us know and we can probably accommodate it, though it will add a few days of "handling time" before we can ship your SensorGnome.
Order turnaround time
We build and test SensorGnomes to order. As a one-employee operation, we aim for a shipping date 10 - 14 days after we receive your order. The turnaround time may be longer depending on order size. However, we will do our best to accommodate shorter turnaround times as necessary.