Here we explain the general theory concerning the relationship between frequency and data rate. This explains why Circuit Design’s products are for the 400 MHz to 900 MHz frequency band and specialize in narrow band.
Concerning use of frequencies, first let’s look at radio, FM, and television broadcasting.
The useable frequency band for radio and television broadcasts differs depending on factors such as effective use of the radio waves, in other words the propagation of the radio waves, the quality of the broadcast, the occupied frequency band width of the modulation system and so on. What is generally called radio is broadcasting using amplitude modulation (AM), and one of the broadcasting frequency bands used for AM is around 6 kHz. FM, in other words broadcasting using frequency modulation (FM), is used for high quality audio broadcasting, and due to these physical characteristics, one of the frequency bands occupied for broadcasts is 150 kHz. With television broadcasts, as the image and sound are broadcast at the same time, the occupied frequency band used for the single channel varies according to the country, but it extends from 6 to 9 MHz. As this suggests, radio broadcasts use the medium waveband (around 500 to 1,600 kHz), FM broadcasting uses the VHF band (around 70 to 110 MHz), and for television terrestrial broadcasting, the VHF and UHF bands (40 to 860 MHz depending on the country) are used.
Next, let’s consider the frequency used for data transmission. For data transmission, since data signals consisting of 1s and 0s are used, rather than the issue of quality as suggested in the previous examples, the relationship between the amount of data that can be transmitted within a unit of time and the frequency band used for this becomes the issue. Circuit Design uses the 400 MHz band and 860 MHz band, known as low power radio and given over to public use in many countries of the world as the so called license free band.　If we take Europe as an example, of the frequency bands permitted by the radio laws in this category, in the 400 MHz band there is a band of only around 2 MHz, and about 6 MHz for the 860 MHz band. In order to use this waveband effectively, how to achieve the stable sending of information is an important point of design using narrowband with a narrow occupied frequency band width. When channel separation is set to 12.5 kHz, 25 kHz or the like within a restricted frequency range, data transmission speed is normally limited to 4,800 bps, with a highest speed of around 9,600 bps. However, in spite of this relatively low speed, narrowband has important merits. Narrow band allows good receive sensitivity on the receiving end, in other words its range can be extended and it is not readily susceptible to interference. In addition, the 400 MHz band frequency can also make use of the ability of the radio waves to make detours unlike with 2.4 GHz used for Bluetooth, WLAN and the like. Improved performance can be expected due to the fact that the radio waves reach the receiver in spite of obstacles. For example, when using high speed data transmission such as for WLAN (10 Mbps or higher), a wide frequency band of nearly 5 MHz is required. Therefore in applications which use this kind high speed data, the 400 MHz band or 860 MHz band for which only a 2 to 6 MHz useable band is permitted cannot be used. So it will be understood that applications which use this kind high speed data can be achieved with the 2.4 GHz or higher bands for which wide band use is permitted.
Many years of research and experience in this area has allowed Circuit Design, Inc. to make reliable products for the 400 MHz to 900 MHz wavebands and to ship them around the world.
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