Radio Telemetry Antennas

We manufacture a variety of antennas used for monitoring VHF signals by hand, or by autonomous systems for wildlife telemetry. Each antenna has a specific application and suits a certain environment or application. The most common types of antennas are yagi-uda (aka yagi), phased arrays, underwater dipoles, and whip antennas.

Keep in mind that the standard RG-58 coaxial cable also has a signal loss of approximately 6.2dB/100ft for 150MHz. Amplifiers and power inserters can be used to boost the signal along a long transmission line, which can also be bought from us here.

Yagi-Uda (Yagi) Antenna

The standard telemetry antenna

yagi-uda on damYagi antennas are the standard radio antenna. They can be mounted to a variety of places such as shorelines, dams, buildings, towers, vehicles, or aircraft. Yagis are directional antennas, which have a large receiving area out the top of the antenna, and a smaller receiving area behind the antenna. These areas generally have a lobe shape, and the size and width of the lobe also depends on the orientation of the antenna. This is called the radiation pattern, and it must be accounted for when setting up the surveyable area.

The elements (pieces perpendicular to the boom) are cut to a specific size to best receive a certain frequency range (+/-2MHz). To get the best results, yagi antennas are usually setup high, pointing the boom at the area of interest. If the animal is being tracked under water, the antenna should be vertically polarized. This is due to the horizontal component of a signal is reflected at the water-air interface, while the vertical component will propagate through. Angle also plays a roll tracking in water, as the signal will be strongest at the Brewster angle of the incoming transmission. Generally, this angle is approximately constant, at about 84° from the normal. If you are tracking terrestrial animals, the Brewster angle is not relevant.

We currently manufacture 3 element Yagis which are made out of light weight aluminum. If you wish to boost the sensitivity of the yagi antenna, two of them can be setup in a phased array.

Underwater Dipoles

Used in turbulent water ways

underwater_dipole

An underwater dipole is much like a yagi antenna, however it is modified for submersed use. Unlike a yagi-uda antenna which has a driven element, reflector element, and at least one director element, the underwater dipole only has a driven element. However, since underwater dipoles are often mounted near the base of dams, the concrete behind the antenna usually acts as a reflector as well. The situation changes if an underwater dipole is thrown over the side of a boat in the middle of a lake, as the receiving area is a donut shape around the driven element.

This type of antenna is suitable for receiving signals in turbulent water ways, deep areas, high conductivity water, and precise locations.

Phased Arrays

Boosting sensitivity by using two antennas in conjunction

yagi_phased

A phased array is when two antennas are setup in close proximity to one another, and in phase so that any signal received has roughly double the strength. This can be done with any antennas, as long as the signal coming in from both is in phase, causing constructive interference.

It is important to setup the phased antennas to be as much of an identical environment as possible. If one antenna is close to a noise source or a reflective surface such as concrete, this will make it more difficult to get the antennas to be in phase with one another.

Whip

The standard omni-directional monopole antenna

Whip antennas are a simple flexible monopole which can be attached to vehicles. The antenna length is determined from the wavelength of the frequency that it should receive. In fact, most vehicles already have whip antennas for receiving AM (~535-1600kHz) or FM (~88.1-108.1MHz) radio waves. For radio tracking, whip antennas are generally cut for the VHF range, most commonly 148-151MHz or 164-166MHz.

These antennas receive signals in a radial fashion horizontally from its orientation. This can be thought of a donut of irradiance, with the point of the whip antenna going through the hole. Although whip antennas have no directional sensitivity, they are often used magnetically mounted on a vehicle for proximity detection of transmitters.