The most critical part is to achieve RF signals transmission
in the whole dynamic torque measure system. Therefore,
choosing the appropriate RF chip is crucial. The RF chip
nRF2401A is an ideal choice, which is made by Nordic
company in Norway. It adopts serial transmission which is
high efficient. Its applications and programming is
relatively simple. It has only two external components.
Only a crystal and a resistor are enough to design RF
circuit, which greatly reduced complexity of the system.
Certain band is occupied by RF transmission. Band is a
resource, and the band is limited. Generally speaking, no
matter organizations or individuals that want to use a band
for wireless transmission, they must apply for a permit to
the local government and pay a management fee. But with
the exception of three bands, the FCC (Federal
Communications Commission) designated three of the
band without a permit, known as the ISM (Industrial,
Scientific and Medical) band [5]. These three bands are: