Low Cost, Low-Power 2.4 GHz RF Transceiver Designed for Low-Power Wireless Apps in the 2.4 GHz ISM B
|Device Type||Smart RF Transceiver|
|RAM size (KB)||1^ 2^ 4|
|RX Current (Lowest) (mA)||13.3|
|Data Rate (Max) (kbps)||500|
|Sensitivity (Best) (dBm)||-104|
|TX Power (Max) (dBm)||1|
|Key Software Features||SimpliciTI Supported|
Receiver Sensitivity (單位: dbm) :這個愈小表示其接收訊號靈敏度愈好。如有一個energy 是-130dbm, Sensitivity 為-140 dbm 的RF, 可以收到感知此訊號, 而Sensitivity 為-120dbm 則感知不到此訊號。
RF power : 功率單位用mW表示, 但常用log表示,在數線上才好表示 dbm 。 dBm=10*log(pf/1mw)
用來表示兩訊號的關係,如SNR (Signal to Noise Ratio)。可以用 Power, 但常用dB來示gain或 decay倍數關係, 如原始訊號被放大一倍, , 用log表示, 則會是說增加了3db
0dBm = 1 mW, 10 dBm = 10 mW, 20 dBm = 100 mW, 30 dBm = 1 W
每增加3db 就是功率增加(gain)一倍x2, 所以功率增加6db就是power x4
每滅少3db 就是功率減少(loss)一倍x0.5, 所以功率減少6db就是power /4
Received Power (dbm) = Transmitted Power (dbm) + Gains (db) − Losses (db)
signal -53dbm, noise -90dbm, SNR= -53-(-90)=37db
一般Wi-Fi 品質叫做好, 那SNR 至少肴 20db (signal是noise旳100倍)
RSSI（Received Signal Strength Indication）是指接收的信號強度指示(in dbm )，用來判定鏈結的品質。
RSSI (Recieved Signal Strength Indicator) is a common name for the signal strength in a wireless network environment. It is a measure of the power level that a RF client device is receiving from an access point, for example. RSSI is the relative signal strength in a wireless environment and can be measured in any unit of power. It is often expressed in decibels (db), or as percentage values between 1-100, and can be either a negative, or a positive value.
The closer the figure is to zero, the better. For example, RSSI of -65 is better than -85. As a general example, a good signal would be -50 dbm, a reasonable would be -75, and a bad one would be -90, while -100 would provide no service at all.
To get a meaniful measurement of a good quality signal, you would have to subtract the noise on the line from that signal power level and consider the difference. A higher difference of signal to noise indicates better signal.
Wi-Fi 發射TX功率,美國 FCC/ 台灣NCC 規範 100mW (20dbm), 通常接收到時的功率只有-50 dbm (因為訊訊在中間傳輸時會loss)