VHF Antennas

Introduction

Telonics provides several antennas for use in VHF conventional telemetry tracking applications. There are two basic types of antennas, directional antennas and omnidirectional antennas.

Omnidirectional or "Omni" antennas are designed to receive signals anywhere within a 360 degree radius. These antennas are not useful in actually locating the transmitter but they can be used to recover data or simply detect presence or absence of the transmitter in a general area. They are often mounted at fixed sites for data collection or mounted on vehicles for purpose of detecting the transmitters during a search.

For a transmitter to be located it is necessary to utilize a directional antenna and to obtain a bearing to the transmitter based upon the direction of maximum signal strength. Using a directional antenna the researcher can either follow the bearing to the transmitter or obtain multiple bearings to the transmitter from several points and locate the transmitter by a triangulation of the bearings.

In the tables below the antennas are divided into two groups; directional and omnidirectional, based on the usage described above. In selecting an omnidirectioinal antenna, the user must balance the size of the antenna against the "gain" or signal gathering capability. Bigger antennas exhibit increased gain characteristics, translating in this case, to the ability to receive the signal at greater range from the animal. Another important consideration is the requirement for "ground plane". Some omnidirectional antennas require ground plane area, which in this case can be a large metal surface under the antenna. In some cases the requirement for a ground plane area might be fulfilled by the large metal roof of a vehicle under a vertical "whip" antenna mounted in the center of the roof. Without a ground plane, the antenna will not perform well, may not exhibit consistent omnidirectional characteristics and range may be reduced dramatically. Thus the signal being searched for may be missed.

In selecting a directional antenna several factors come into play. The more elements that the antenna has, generally the higher the gain of the antenna. Users should understand that antennas with more elements are physically larger and antennas with 5 or more elements are not very good for handheld applications. The size of the antenna prevents the handheld user from deploying the antenna correctly and though there is more theoretical antenna gain the larger antenna often performs poorly relative to a smaller antenna which can be deployed properly in a handheld application. Larger directional antennas (more elements) must be deployed correctly to perform well. First, they need to be elevated on a mast and be kept away (ideally 4 meters minimum in the VHF frequency range) from all conductive materials (including the earth below and wet vegetation above). An antenna elevated on a mast into the moist leaves of a tree canopy will not perform well. A large directional antenna mounted too close to the metal body of a vehicle will be detuned and the directionality compromised. In addition to more gain, most "Yagi" Antennas (multiple element directional arrays) exhibit a narrower beam width as number of elements is increased. This narrower beam width is often misinterpreted to mean that antennas with more elements are "more accurate" in terms of the bearing angle. This is not necessarily true. To achieve significant improvement in bearing accuracy the RA-NS systems (two antennas arrayed together) are a much better choice for obtaining repeatable high accuracy bearings. Individuals looking to achieve high accuracy bearings using these systems may refer to the page describing the RA-NS system, its theory and its practical operation in the field.

Telonics specifies gain measured in decibels (dB) relative to a standard dipole (dBd). The user should be wary when comparing Telonics' specifications for antennas to other manufacturers measured or expressed relative to an isotropic point source (dBi) which may seem superior but, in fact, are not.

To assure performance, all Telonics antennas are assembled, tuned, and tested for the specified center frequency, bandwidth and VSWR characteristics prior to shipment.

As always, if you have any difficulty selecting the proper antenna to meet your study requirements, please contact Telonics. Our engineering staff will be pleased to assist you in the selection of an appropriate antenna.

Details

For applications outside the standard wildlife telemetry bands of 148 to 174 MHz, please consult Telonics. Unless otherwise specified, antennas are not supplied with coaxial cables, e.g. RW-2, RW-3, RW-5, to connect the antenna and receiver. For RA-2AK, RA-14K, RA-5A, RA-5B, and RA-10, Telonics supplies coaxial cables and BNC connectors. If a longer cable is required, you may purchase the appropriate coupler, e.g. CON-BNC/BNC-J/J, and additional cable separately.

Antenna Accessories
Coaxial Cables
Coaxial Connectors

Models

How to use this table: The information contained in the following table is provided in a manner to allow comparison of models. To sort by model attributes i.e. weight, CLICK ON THE COLUMN HEADING. To obtain more specific information for a model, CLICK ON THE MODEL NUMBER.

Directional Antennas

Model	Name/ Description	Number of Elements	Antenna Gain	Connections	Handheld	Fixed Site	Land Vehicles	Boats & Ships	Aircraft
RA-1A	paddle (loop)	0	-8 dBd	Cable not included BNC female
RA-2AK	"H" type	2	4 dBd	WI-000496-001, 5ft. cable included BNC female
RA-14K	rubber ducky "H" type	2	4 dBd	WI-000496-001, 5ft. cable included BNC female
RA-19K	flexible "H" type	2	4 dBd	WI-000496-001, 5ft. cable included BNC female
RA-7	2 element folding	2	2 dBd	Cable not included BNC female
RA-17	3 element folding	3	4 dBd	Cable not included BNC female
RA-3	Yagi	3	6 dBd	Cable not included pigtail connection
RA-4A	Yagi	5	9 dBd	Cable not included pigtail connection
RA-4B	Yagi	8	11.8 dBd	Cable not included pigtail connection
RA-4C	Yagi	14	13 dBd	Cable not included pigtail connection

Omni Directional Antennas

Model	Name/ Description	Antenna Length	Antenna Gain	Connections	Handheld	Fixed Site	Land Vehicles	Boats & Ships	Aircraft
RA-5A	5/8 wave whip with magnetic mount	46.75 in	3 dBd	Integral 12 ft. cable with BNC male connector
RA-5B	5/8 wave whip	46.75 in	3 dBd	Integral 17 ft. cable with BNC male connector
RA-6B	stacked collinear	10 ft	3 dBd	Cable not included UHF connection CON-BNC/UHF-J/P adaptor included
RA-8	quarterwave rubber ducky	7.25 in	-3 dBd	Cable not included BNC male
RA-10	ground plane independant halfwave	46.75 in	0 dBd	Integral 20 ft. cable with BNC male connector
RA-11	fiberglass monopole	20 in	0 dBd	Cable not included BNC female
RA-18	vertical collinear Omnidirectional ground plane independent	8 ft	3 dBd	Integral 20 ft. cable with BNC male connector
RA-20	vertical collinear Omnidirectional ground plane independent	8 ft	3 dBd	Integral 15 ft. cable with BNC male connector
RA-21	vertical collinear Omnidirectional ground plane independent	4 ft	0 dBd	Integral 20 ft. cable with BNC male connector
TA-9	quarterwave Omnidirectional with ground plane	33 in	0 dBd	Cable not included BNC female