We get asked that a lot, and for good reason. Everyone wants to find their animal, and they want to know how close they need to be before they can pick it up on frequency before calling it a day. The answer varies; there are numerous variables, and the variables are always changing!
Let’s start by saying that VHF tracking is line-of-sight. That means that the receiving antenna has to “see” the transmitting antenna before a signal can be heard, and vice versa. Anything that is in the way of that line-of-sight path will attenuate, or degrade, the signal. This includes light or heavy brush, trees, and most definitely, mountains. And if the animal goes behind a crop of rocks or decides to lay down, there goes your range.
Many times, the best way to increase range is to hold the antenna higher up off of the ground. To really increase range, get in an airplane and track – you’ll have excellent line-of-sight and very good range, many miles in fact.
Another big influence on range is the type of receiving antenna used in your field work. One simple way to increase range is by using an antenna with more elements on it, e.g. a four element antenna instead of a three element one. A directional type antenna will provide better range than a dipole antenna, which only has one element. An excellent paper, Selecting Receiving Antennas for Radio Tracking is available on the ATS website.
Also, using a narrow band receiver designed specifically for telemetry will increase range, especially one that includes digital signal processing (DSP) capability. The ATS R4500 series of telemetry receivers are a good example. Their band width is 4 MHz, and a DSP chipset is used; better performance than a receiver with 8 or 16 MHz band width and lacking DSP.
Finally, the transmitter design itself will influence reception range. A longer antenna will increase range, and use of a three stage circuit will too. ATS offers the option to include a three stage circuit in some models. This will provide you with a stronger signal than a standard transmitter circuit, but at the expense of battery life, since the power output is higher.
If you have additional questions about how you might increase the range of your radio telemetry system, please call us at ATS.
Two directional Yagi antennas installed on a tall tower for excellent line-of-sight range!