Last update, 09/08/2010 © 2008 Farell Instruments	Here is a selection of the questions our customers most frequently ask. SELECT THE WIRELESS EQUIPMENT FOR TELEMETRY Is any engineering necessary before ordering wireless modem equipment? Radios: licensed or unlicensed? The quality of this link is insufficient. Can I have a higher RF output power? What prior knowledge is required to install the radio equipment? Can Farell Instruments install the radio equipment it sells? Which kinds of radio telemetry equipment require a licence from the government? What are the advantages and disadvantages of using licensed frequencies? What are the advantages and disadvantages of unlicensed band use? Is any engineering necessary before ordering wireless modem equipment? Yes. First of all, you must define your radio network properly: 1) Identify where your equipment will be placed and the geographical co-ordinates. 2) Identify the network topology: which points are interconnected. 3) Identify the frequency you will be using, or at least, the band on which it is to be located. 4) Identify the equipment (carrier power, data speed) and aerials (gain and type). 5) Identify the communications protocol and ensure that data speed is high enough. 6) Calculate the radio-link quality: optimal > - 70 dBm at RF port, minimum > - 90 dBm. If you have the information required under points 1) and 2), Farell Instruments' Technical Support Service can help you define the rest. Radios: licensed or unlicensed? It all depends on the application. If the application is critical, or the network covers a large geographical area, or radio channel occupation rate is high, you will need to use a licensed frequency. This will ensure that the application will work well against possible interference (or if interference occurs, you can ask the government telecommunications service to locate and eliminate the interfering source). However, if you use an unlicensed frequency (433 MHz, 868 MHz or 929 MHz) you risk other surrounding radio systems interfering legally whilst your application is operating. The quality of this link is insufficient. Can I have a higher RF output power? There are legal limits to the maximum RF trasmitted power in every country (typically 0.5 to 0.1 Watt on unlicensed frequencies and 10 Watts on licensed bands). There is also a technological limit to the transmitted power on all equipment. Increasing the RF output power of the radios or using external amplifiers reduces the meam time between fails (MTBF). It is, then, recommended that you limit your system to the standard RF output power provided by the equipment and, above all, to legal levels. Installing a repeater to eliminate links of doubtful quality is always more reliable and will avoid you running into problems with the telecommunications authorities. Farell Instruments is not liable for any user installations using illegal transmitted RF power levels. What prior knowledge is required to install the radio equipment? For simple networks, basic knowledge of aerial and coaxial cable will be enough, plus the capacity for configuring the basic parameters of the radio through the serial port: the Tx and Rx frequencies, serial port speed… It’s very easy! Once installed, the wireless modem will behave transparently, as though you had connected the two terminal devices (PLC or others) via cable. Farell Instruments' own wireless modems have a Received Signal Strength Indicator (RSSI) and systems for testing channel occupation and link quality (Link-test and Scanner option), to make installation testing very easy. Can Farell Instruments install the radio equipment it sells? Farell Instruments is a manufacturer and, as such, it NEVER installs its own equipment. If you are not capable of installing and maintaining your radio network yourself, we have expert customers and distributors who can help you. Which kinds of radio telemetry equipment require a licence from the government? All wireless data equipment installed on a private band (i.e. for the exclusive use of a single user) requires a government licence. Generally, all band frequencies for the transmission of data are licensed. However, there are certain free (unlicensed) frequencies, around the 433 MHz and 868 MHz level (Europe, ITU Region 1), 929 MHz (America, Australasia, Asia ITU regions II and III), and 2.4 GHz. What are the advantages and disadvantages of using licensed frequencies? Advantages: It avoids interference with other services or applications. It allows unlimited transmission and channel occupation time. Disadvantages: You need to file for a licence. You must pay an annual fee for the use of spectral space. What are the advantages and disadvantages of unlicensed band use? Advantages: They are free and can be used immediately. You do not have to file for a government licence. Disadvantages: Possible legal interference from other systems. Limited percentage of transmission time. Limited maximum transmitter strength (thus, shorter link range than with licensed systems).