Which is the best frequency to use for my application: 315MHz, 418MHz, 433.92MHz, or 900MHz?

315MHz is primarily used for remote keyless entry (RKE) systems and garage door openers. As a result, this frequency is somewhat crowded, increasing the chances for interference. The FCC allowed power is lower than 418MHz or 433MHz and the selection and efficiency of antennas is limited.

418MHz is a good frequency to use in the US as it is not very crowded. This gives the least likely chance for interference and therefore the best performance.

433.92MHz is primarily used for RKE applications in Europe. It is also a popular frequency for active RFID tags which can have a range of up to 1000 feet. It is not good for use in the US because of the chance of interference from amateur radio and the nearby pager band.

868MHz-870MHz is an unlicensed band in Europe. The band is subdivided for different applications, but there are not many restrictions on the type or duration of data. Unlike the 902MHz-928MHz band in the US, there are only 2MHz to support many applications, so the band has become somewhat crowded.

902MHz-928MHz is more versatile than the 260MHz-470MHz band in the US because the FCC has only specified the output power and harmonic levels. There are no restrictions on the type or duration of data that can be sent. This gives the design engineer a great deal of freedom in the possible applications, but also results in the band being more crowded. A disadvantage for cost-sensitive applications is that 900MHz modules are typically more expensive due to the more complex filtering and modulation required for link reliability at these higher frequencies.

Review AN-00125: Considerations for Operation Within the 260-470MHz Band, AN-00126: Data and Bidirectional Transmissions under Part 15.231, AN-00130: Modulation Techniques for Low-Cost RF Data Links and FCC Title 47 for more information. A resource document containing a hard copy of the application notes ships with every Linx evaluation kit. You may obtain a hard copy of FCC Title 47 from your local government bookstore or from the Government Printing Office in Washington.