A Motus station consists of three main components:

• Receiver: this is the computer which records and stores the radio data

• Antennas: there are several types of antenna designs. They are 'tuned' to listen to a narrow range of frequencies. Each antenna gets its own coaxial cable and depending on the receiver type and listening frequency, it's own 'dongle', or USB devices which listen to a specified frequency range (i.e., software defined radio).

• Power supply: this provides power to the receiver. Most off-grid stations us solar power, but AC power is most reliable. The number one reason for a station to malfunction is a power failure.

How to select an antenna

It is very important you select the right antenna for the purpose of the station and the type of tags you intend to detect. Antennas are optimized for reception on a particular radio frequency. Since there are multiple tag frequencies, each tag type requires its own antenna; currently an antenna optimized to detect Lotek tags on 166.380 Mhz will not detect CTT tags on 434 Mhz, and vice versa. Wherever possible we recommend installing “dual-mode” stations outfitted with antennas and a receiver that can detect both tags. A dual-frequency antenna is under development, but for the time being, dual-mode stations (those that can listen for more than one frequency, must have two different types of antenna in place.

How antennas work

An antenna is a device used to send or receive radio signals, i.e., electromagnetic radiation. This radiation induces a voltage in conductive materials which will vary in magnitude based on the physical dimensions and orientation of the material. The induced voltage oscillates at the same frequency as the electromagnetic radiation and the magnitude of the voltage is proportional to the strength of the radiation. Antennas used in the Motus Network are built (“tuned”) with high precision such that the induced voltage is greatest when exposed to the narrow range of frequencies that Motus tags emit. Antennas can also be shaped to select for radiation from specific directions and orientations.

Each antenna has a theoretical radiation pattern which represents its range in 3D space. We use the radiation pattern to predict the distance and direction in which we can receive signals from radio transmitters. Omnidirectional (‘omni’) antennas, as the name suggests, have a uniform radiation pattern that is emitted perpendicular to its axis. The thin wire attached to Lotek and CTT tags is a type of omni antenna. When used on a receiver, omni antennas provide presence/absence information, typically within a short range. This makes them ideal for fine scale studies as demonstrated with CTT SensorNodes which can be used to create a high-resolution grid of stations.

Left: A torus, representing the electromagnetic radiation pattern of an omnidirectional antenna (CC BY-SA 3.0, source: Wikipedia). Right: Cross-sectional view of a half-wave omni-directional antenna (public domain, source: Wikipedia).

Yagi-Uda (‘Yagi’) antennas are a type of directional antenna that are the most commonly used antenna in the Motus network. Their radiation pattern is directed into a beam which varies in length and width based on the number of ‘directing elements’ with a greater number of elements resulting in a longer, narrower beam. For example, a 9-element Yagi antenna can theoretically provide tag detections from 15 km away at 166.380 MHz, but in reality this will vary widely based on the landscape and atmospheric conditions. Yagi antennas are favorable for most applications since they can be used to create receiver ‘fences’ or ‘grids’ with fewer stations than an omni antennas could. In addition, multiple Yagi antennas on a single station can be used to infer flight direction based on the timing of detection across each antenna.

A variety of antenna options exist for VHF/UHF telemetry. To date, collaborators have used 3, 5, 6, and 9-element Yagi directional antennas, and omni-directional antennas. Generally the greater the number of elements, the longer the detection range and more narrow the detection beam. The fewer the elements, the shorter the detection range, but the broader the detection beam. Omni-directional antennas are best suited for determining species presence-absence patterns (e.g. seabirds at a colony), or for detecting birds in close proximity to stations (within a few hundred metres), not suited for providing directional information (e.g. departure directions of songbirds from a stopover site).

Large Yagi antennas are useful for making receiver fences and grids since they can be spaced as far as 30 km apart with antennas pointing towards each other to capture animals passing in between. Mid-sized Yagi antennas provide a compromise between distance and “field of view”, or width of the detection beam. Small Yagi antennas are typically used for manual tracking, or for monitoring animals within a small study area. CTT Nodes have small omni antennas with a line-of-sight (LOS) range of around 1.4 km which if distributed in a grid can provide highly accurate location estimates. See array design above.

Ordering Antennas

When ordering antennas and cables, it is important to ensure:

1. Connectors between the coaxial cable, antennas, and receiver are compatible.

2. The impedance rating of all cables, connectors, and dongles are the same (50 Ohms).

3. Cable type is suitable for the length needed.

4. Get recommended equipment if inexperienced with the technology (highlighted in green).

Select an item from the list below to learn more:

• Antennas

• Coaxial Cables

• Radio Dongles

• Connectors

Antenna Anatomy

Yagi-uda

This antenna, usually referred to as simply “Yagi” or more generally a directional antenna.

Antenna Types

A variety of antenna options exist for VHF telemetry. To date, users have used 3, 5, 6, and 9-element Yagi directional antennas, and single-pole omni-directional antennas. The 9-element Yagis have a long, narrow detection range, whereas 3, 5, or 6-element Yagis have gradually shorter and wider detection ranges. Omni-directional antennas are best suited for determining species presence-absence patterns (e.g. seabirds at a colony), or for detecting birds in close proximity to stations (within a few hundred metres), but not for providing directional information (e.g. departure directions of songbirds from a stopover site).

When ordering antennas, it’s important to know what frequency you need it to be tuned to. For detecting Lotek tags, antennas must be tuned to 150.1 MHz (Europe), 151.5 MHz (Australia), or 166.380 MHz (Western Hemisphere), depending on the region. For detecting CTT tags, antennas must be tuned to 434 MHz.

Antennas can be purchased from the following suppliers:

• Laird (through Hutton in Canada Economy 2-way in US)

• Wade Antenna [LINK]

• Maple Leaf Communications

• Digikey

Use the table below to help select your antenna:

Coax Cables

Coaxial cables (coax for short) are responsible for carrying the received radio signal from the antennas to the receiver. This cable is so-called coaxial because it contains a central conductor surrounded by a second conductor that runs coaxial to the central conductor (around it). This second conductor is electrically connected to the ground plane and provides shielding that helps insulate the central signal-carrying conductor from external electromagnetic interference and also reduces the amount of energy lost from the central conductor. Between the central core and shielding is a layer of insulating material which can vary in thickness, as well as the plastic outer jacket of the cable.

The signal carried by coax is measured in decibels (dB) and calculated by comparing the power coming out of the coaxial cable to a theoretical 1 mW transmitter.

With this equation in mind you can see how an increase of 3 dB actually means a doubling of the received power. Antenna resistance is an intrinsic property of the antenna and usually runs at 50 Ω. The coaxial cable also has a resistance so it will reduce the power of the incoming signal which varies by frequency. This is known as attenuation.

When selecting coaxial cables, you want pick something that keeps attenuation to a minimum. Attenuation can’t be eliminated entirely, so we try to keep it within a reasonable limit. For weak signal detection a difference 0.2 dB can be significant. The supplier for our coaxial cables and antennas here in Canada (Maple Leaf Communications) has suggested we try to keep attenuation under 1.0 dB for any cable length, but obviously this is not always practical. The recommended low-loss cable is the LMR-400, but it is very bulky and difficult to work with. For this reason, we recommend using lower grade cables for short lengths, such as the LMR-240 or RG-58.

To get an idea of what kind of effect attenuation may have on tag detection, imagine a receiver with a theoretical detection radius of 10 km. If the antennas on the receiver experienced 1.0 dB of attenuation, this radius would be reduced to 9 km; if they experienced 2.5 dB of attenuation, that would be reduced to 7.5 km.

Signal loss by length of cable

One of our antenna equipment suppliers, Maple Leaf Communications, has written a helpful guidance document for selecting cables based on the length and frequency required.

Additional documentation

A helpful guide on coaxial cables can be found on the Wilson Amplifiers website

A catalogue of cables and their specifications can be found on Allied Wire & Cable. But briefly, we use:

• RG58 – basic communications cable that typically comes with a BNC connector. Best used for lengths less than 50′. The least expensive option.

• RG213 – higher grade cable that can be used at length of up to 100′ with low signal loss. Custom cable ends depending on distributor/manufaturer. Moderate price.

• TWS/LMR-400 – similar to the RG-213, but higher quality (stronger weather/sun resistance) coating. Best for longer-term installations and long cable length. Most expensive. Manufacture can suggest which cable is best for your needs – LMR is generally more affordable.

• BMR-240 - available from Maple Leaf Communications, this cable has slightly less plastic insulation, making it much more flexible and easier to work with than LMR-400, while offering similar attenuation.

Radio Dongles

Radio dongles, also known as Software Defined Radios (SDRs), are used to convert analog signal received by the antennas into a digital signal that can be interpreted by the SensorGnome . Note that Lotek receivers have a built-in converter and do not require these for station operation. Note that SensorStations only need an SDR for antennas tuned for Lotek tags (anything that isn’t 434 MHz).

While there are dozens of available SDR’s on the market, only four models are compatible with SensorGnomes and SensorStations. Most commonly used are the FUNcube Pro Plus which have the smallest signal-to-noise ratio (SNR), noise figure, and DC voltage spike (poor reception at nominal frequency), and power rating. However, FUNcube dongles are the most expensive, costing ~$200 USD, compared to $35 USD for the RTL-SDR.

* CTT dongles listen to 434 MHz and are only used to make Sensorgnomes compatible with CTT tags.

Items listed in green are recommended.

Bandpass Filter

Connectors

There are several types of connectors that are used with radio antennas and coaxial cables, but not all perform equally. For instance, certain connectors are better at preventing water and dust ingress. For this reason, it’s important to know what kind of connectors your antennas have when being purchased, and which are most suitable for a Motus station. There are four connector types commonly found in Motus station setups: UHF (PL-259); N-type; BNC; and SMA.

Most 9-element Yagis and omni-directional antennas tend to come with a female UHF (Laird) or N-type connector (Maple Leaf), but this should be verified prior to purchase. Three and 5-element Yagis usually come with a male BNC connector and so they can be connected to a Lotek SRX receiver directly, or to a FUNcube with female BNC to male SMA adapter.

The following table outlines where we typically see these connectors. Dongles are the analog-to-digital converters that are part of the Sensorgnome (typically we use FUNcube dongles, or FCD).

Items listed in green are recommended.

The following are some common uses of these connectors:

1. Coax cable with male BNC connector at one end and male UHF connector at the other end (for Lotek receivers or Sensorgnomes with female BNC to male SMA adapter).

2. Coax cable with a male BNC connector at both ends with a BNC female to UHF male adapter (Lotek receivers or Sensorgnomes with female BNC to male SMA adapter).

3. Coax cable with custom female UHF connector at the antenna end and a male SMA connector at the FUNcube end. (Option with fewest adapters and therefore less signal loss, but may be more expensive due to custom ends). Sensorgnome only.

Grounding Antennas

In some locations, it may be necessary to ground your antennas in case the station is struck by lightening. In regions where thunderstorms are frequent, Motus stations that are not adequately grounded can ignite fires. For instructions on how to ground your station as well as a list of required equipment, see Grounding Antennas.

Power Sources

Receivers can be powered by either AC or DC. AC power supplied by mains should be used whenever possible as it is generally a more reliable and cheaper power supply than DC. DC supplies usually come in the form of Deep Cycle batteries and require regular charging via solar or another method to maintain power. Also keep in mind that since DC typically requires a solar panel and battery it is a more attractive target for thieves.

AC Supply

If using mains AC power from a typical wall outlet, ensure you use a good quality power adaptor that is rated for the mains power of that region (e.g.: North America is 120 Vrms @ 60 Hz; South America is highly variable, 115-230 Vrms @ 50 or 60 Hz). A good quality adaptor can tolerate this variation in mains voltage which makes them more versatile for projects across multiple countries. A poor quality adaptor will produce an unstable voltage which can damage a receiver or not produce enough power to keep it operational. You may also want to connect your station through a proper surge protector.

The type of adaptor required will depend on the type of receiver being used. For CTT SensorStations and Lotek SRX receivers, these power supplies are usually included with the receiver. SensorGnomes will also be shipped with an AC power supply when ordered through Compudata or RFS Scientific.

If you do not have a power adaptor for your SensorGnome receiver, you can use a standard USB power supply for your phone (“fast charger” or minimum of 2.5 Amps) with a USB cable. For CTT or Lotek receivers, contact your supplier to purchase an adaptor.

If mains power is unreliable and 24/7 coverage is needed, then you may wish wish to connect your station through a battery powered backup power supply.

DC Supply

Powering electronics directly from DC is more complicated since there is no single setup for all stations. Instead, the type and amount of power required will depend largely on region and available resources. In order for a station to be compatible with a DC power supply, it must have a method for converting the voltage of a battery - usually 12 volts - to something the receiver can handle, which ranges from 5 to 18 volts, depending on the model.

• CTT SensorStations have built-in voltage converters, allowing them to accept a direct connection to the battery; however, in practice NEVER connect your receiver directly to the battery without a low-voltage cutoff to protect your battery.

• SensorGnomes require a DC buck converter to lower the voltage down to 5 volts. This component is standard when purchasing from Compudata. Buck converters are only provided in SensorGnomes if requested by RFS Scientific.

• Contact Lotek or see your receivers user manual for more information on SRX series receivers.

Battery

Type

Lead-acid batteries are based on very old technology, but still provide the cheapest, non-volatile power storage for electronics. Lithium-based batteries offer the highest energy density of any commercially available battery, yet they are far more expensive relative to the power they store. In addition, Lithium-based batteries are typically far more volatile, risking chemical spills and fire if they are charged/discharged too quickly, if their temperature is too high or if they are punctured. For these reasons we do not recommend Lithium-based batteries unless space and weight is very limited. Since lithium-based batteries are used so rarely in the Motus network, they will not be discussed further here.

Most people refer to 12-volt lead-acid batteries as “car batteries,” but in this instance you might get the wrong type if that’s what you ask for. This is because car batteries are not designed to be discharged over long periods of time and require constant top-ups, such as from a car’s alternator. In a Motus station, batteries must be able to go down to voltages as low as 10-11 volts each night without losing much capacity - this would ruin the typical car battery in no time!

This is why we use deep-cycle batteries which allow a deep discharge during each charging cycle. Most deep-cycle batteries that are readily available are marine grade (a.k.a.: “marine battery”) which are designed around offering high cranking amps to start up large boat motors, but this is not anything we need in a radio station. Nonetheless, in remote locations with nothing else available, a marine battery will do. While more expensive, specialize solar deep-cycle batteries are also available that are designed provide small amounts of power continuously and varying degress of recharging.

You may also notice there are flooded and sealed lead-acid (SLA) batteries that exist. This refers to whether the internal chemistry can offgas externally. Flooded lead-acid batteries are well known for producing highly flammable hydrogen gas and can be extremely hazardous if not stored in a well-ventilated area. We usually store batteries in a closed tupperware bin which increases the potential of this hazard which is why we recommend SLA batteries. Even so, batteries should be handled with care so as to not puncture the battery casing, potentially allowing the slow release of hydrogen gas over time.

We recommend the following batteries, depending on application:

Capacity

Battery capacity is recorded in Amp-hours (Ah) or Watt-hours (Wh) which is a measurement of current or wattage consumed multiplied by the amount of time current flows. This is helpful because we can easily calculate the amount of Amp-hours we expect our receiver to consume by reviewing the power consumption table or by measuring the current of a connected receiver using a voltmeter. Put simply, a SensorGnome which consumes 0.5 A of power at ~12 volts can theoretically run off a 50 Ah battery for 100 hours (50 Ah / 0.5 A = 100 h). Keep in mind that you won’t ever use the full capacity of a battery since it should not be discharged below 10.5 volts (see Undervoltage Protection). In addition, the capacity will slowly decrease over time with each discharge of the battery, so ensure you add an extra 10-15% of capacity to account for this drop over time. Batteries vary in performance at different temperatures as well and average a shorter lifespan in warmer climates.

When shopping for batteries, we recommend a 50 Ah battery for day lengths greater than 12 hours and a 75 Ah for day lengths under 12 hours.

Cold weather

For cold weather conditions, we recommend self-heating Lithium iron phosphate batteries, however there are some risks involved with deploying this type of battery. While the chemistry is stable and unlikely to combust like typical Lithium-ion batteries, they will be damaged if they are charged when below 0 C (32 F). Self-heated batteries are rated to temperatures as low as -20 C and have protective circuits to prevent them from damaging themselves. Batteries can be charged at even lower temperatures if they are stored in an insulated box. More information about storage and use of Lithium iron phosphate batteries can be found in the PDF below.

Undervoltage Protection

When using any type of battery to power a station, it is recommended to always use undervoltage protection so you do not ruin your battery. While your station may function without one, it greatly reduces battery life and will eventually result in the battery not holding any charge. If using a solar panel to charge the battery, you will require a charge controller with low voltage cutoff. Without a charge controller, you will need to buy a low voltage cutoff, also known as an undervoltage protection module.

We recommend Sunsaver charge controllers with low-voltage cut-off - minimum 10L (depends on size of solar panel), Specifically XXX, and any solar panel (minimum 90 watt).

Solar Power

Type

Just like batteries, choosing the right solar panel for your setup can be a daunting task considering the number and types of panels available, but usually your local wholesale retailer of solar panels can help you with picking one out. There are a few different types of solar panels, but the two main ones we deal with are monocrystalline and polycrystalline. The main difference between the two is that monocrystalline cells are on average more expensive, but provide more efficiency and have greater heat tolerance; however, performance appears to vary considerably by manufacturer. Panel efficiency is not necessarily important considering the relatively small panels that we use to begin with. Heat tolerance may be an important consideration in more southern latitudes; we recommend speaking to local suppliers for their recommendation. We generally recommend polycrystalline solar panels to save on costs.

Wattage

The amount of power your panel needs to produce depends on the amount of sun exposure you expect on the shortest day of the year. In Canada, 80 Watt panels have been effective for ¾ of the year, but do not produce enough for continuous operation in the winter. For continuous winter operation, we have been recommending at least 150 Watts by industry experts. In the summer, 50 Watt panels have been sufficient.

Charge Controller

All solar panel setups require a charge controller. This is the device that mediates the power flow between the solar panel and the battery, keeping the panel from overcharging the battery, and ensuring electricity doesn’t flow into the panel at night when the panel voltage drops. We recommend getting a charge controller that also includes undervoltage protection, or ‘low-voltage cutoff’, to further protect the battery from getting overly drained by the receiver, or ‘load’. If your charge controller does not have undervoltage protection, a separate device should be used between the battery and load. See undervoltage protection for more details.

The charge controller most often used by Birds Canada is the MorningStar SunSaver SS-10L-12V. This can charge a 12-volt battery with up to 10 Amps of current and includes a low-voltage cutoff. These have proven robust and longer-lasting than cheaper models, but they can still fail so it’s always important to have spares around.

Power Outages

The main issue is that if the power happens to cut out when the receiver is writing to its storage, it could corrupt the storage and prevent the receiver from ever booting back up.

AC Power

Some sites have AC power available, but there may be problematic power outages. To get around this, you will need an uninterruptible power supply -- or UPS. They come in various shapes and sizes, based on the device being used and the amount of power you intend on drawing.

A generic UPS is commonly available at local electronics stores as they are often used to protect databases and servers. The ratings of UPS can be difficult to interpret, so its important to look at the spec sheet to identify how long it lasts while under load. Usually, it's reported as the number of minutes under full and half load which can be used to calculated the length of time the receiver will last based on the expected load of the receiver. Motus receivers use very little power (usually less than 5 Watts) so you can expect it to last much longer than what is typically advertised.

For example, a UPS on Amazon is rated for 510 Watts and it has a spec sheet that says it lasts for 6 minutes while under half load. That means the battery has a theoretical capacity of (255 Watts) * (0.1 hours) = 25.5 Watt-hours (Wh). That means you can expect a 5 Watt load to last 25.5 Wh / 5 W = 5.1 hours (in theory, probably less in reality).

If you can find the manufacturer specifications you should be able to get more accurate results by using the battery hardware specifications. For example, the CyberPower SX950U-FC has the battery size in the spefications listed as (12 Volts) * (7.2 Amp-hours) = 86.4 Watt-hours. That means a 5 Watt load would last 86.4 Wh / 5 W = 17.28 hours (probably less due to conversion losses).

The nice thing about getting a generic UPS is that nearly all of them also have surge protectors which is important when you have an unreliable AC power supply. However, it's a good idea to test any system if the battery capacity is an important factor in your purchasing decision.

Raspberry-pi based SensorGnomes can use a UPS HAT, but these systems have not been adequately tested so aren't recommended for regular deployments.

Solar Power

Receivers

Not all receivers are compatible with all tag types! Read more about receivers here.

Antennas and cables

166.380 MHz antennas

For Lotek Nanotags in the Western Hemisphere.

434 MHz antennas

For CTT LifeTags, PowerTags, and HybridTags globally.

Laird 6-Element Yagi TS4306

Coaxial Cables

Most RF or antenna suppliers will sell coaxial cable cut to size and with with your choice of connection type. We recommend LMR400 cable, which is durable and low-loss. However, due to its stiffness, we also recommend a 30 cm (12-inch) jumper cable made of a lighter grade material (e.g.; LMR-240) as strain relief for connectin between the LMR-400 cable and the FUNcube dongle. Alternatively, you may use bulkheads for strain relief.

Bulkheads

Bulkheads are connectors used to attach coaxial cables to the receiver. They attach directly to the 'radios' or 'dongles' which are part of the receiver (e.g.; CTT internal radios or FUNcube dongle). These parts can be readily found online at various retailes, just make sure you search for SMA male to Type N female bulkhead. We recommend waterproof bulkheads for mounting on cases - these come with o-rings which can maintain the original IP rating of the case. The product below is a somewhat expensive example of what we normally purchase, yet we are usually able to find the for under $10 USD apiece at other retailers.

Bandpass Filters

Power Supply

Antenna mounting structure

The Motus Network mostly consists of stationary automated radio telemetry stations which continuously record incoming radio pulses. Mobile stations also exist, either affixed to a moving vehicle, boat, or in a backpack on foot. Other receivers are used for manual tracking so that wildlife can be located in and observed in-person for more precise location data.

Automated Telemetry Receivers

There are three types of receivers compatible with Motus that can be purchased, or built yourself in some cases: Lotek Wireles Inc (SRX600, 800 and D-series receivers), CTT Sensorstation and Nodes, and the open-source SensorGnome.

Sensorgnomes can be purchased from Compudata or RFS Scientific or built with the following instructions. Note these instructions are very outdated and require revision. New instructions will be posted in the near future.

(1) Price does not include cost of: Wi-Fi module; cellular module; data plans; case; power supply; bulkheads (1 required per antenna); or testing time.

(2) CTT charges $5/month base plus data costs for cellular data plans and an additional $5/month for station health reports. Contact CTT for more details.

(3) Cost for self-built SensorGnomes is estimated to be ~$150 USD without dongles, but prices may vary. Instructions on building SensorGnomes can be found here and here, but note these are outdated and require revision. New instructions will be posted in the near future. We do not recomend collaborators build their own SensorGnome without prior experience.

Manual Telemetry Receivers

For manual telemetry, we need a portable receiver that can decode tag IDs in real time.