According to the Bluetooth protocol version specifications of different DUTs, from BasicRate (BR) of BT 1.0 to Enhanced Data Rate (EDR) of BT 2.0 to Low Energy (LE) that began to appear in BT 4.0. The Bluetooth Special Interest Group (SIG) maintains the core Bluetooth specifications and has been looking for expansion and balance on power consumption, speed, and the latest Internet of Things functions.

The first is the same point. The BR/EDR, LE and AMP RF of Bluetooth devices all use the 2.4GHz ISM (Industrial Scientific Medical) frequency band, and the frequency range is 2.400-2.4835 GHz.

Figure 1. Schematic diagram of Bluetooth frequency and RF channel number

The difference is that the operating frequency of the BR/EDR mode device is divided into 79 channels within the ISM frequency range. Each channel occupies a bandwidth of 1MHz. A guard band (protection bandwidth, Lower Guard Band) is set up outside the 0 channel and the 78 channel. 2MHz, Upper Guard Band is 3.5MHz).

The operating frequency of the equipment in LE mode is divided into 40 channels within the ISM frequency range. Each channel occupies a 2M bandwidth. A guard band is set up outside the 0 channel and 39 channel (protection bandwidth, low frequency Lower Guard Band is 2MHz, high frequency Upper Guard Band is 3.5MHz).

In addition, it should be noted that the default signaling mode of Bluetooth devices is frequency hopping pattern. When doing non-signaling radio frequency testing, you need to set the DUT to a fixed frequency mode to facilitate continuous transmission or reception. Do statistics and analysis of test signals.

The WT-20x series equipment and WT-328 equipment of the Extreme Instrument Company support the transmission and reception of carrier signals in the 2.4G frequency band, and have prefabricated test waveform files for Wi-Fi, BT, Zigbee and other related modes, which can be used Do turnkey (Turn Key) test system or production system integration.

Figure 2. WLAN meter software interface of wt-20x device

When testing the radio frequency indicators of Bluetooth signals, you need to use the tools provided by the chip manufacturer to switch the operation mode to non-signaling mode, and manually configure the DUT to transmit specific payload data packets at different frequencies, such as 01010101 Or 11110000 payload. For different debugging tools, different channel numbers range 0~39, 1~36, 0~78, etc. may be displayed. This article will focus on how to do it on the WLAN Meter interface of the WT-20x instrument test software and the DUT configuration interface. Correct pairing settings.

This time I take the Bluetooth debugging tool RTLBTAPP of Realtek manufacturer as an example. If the chip specification of the tested object supports EDR, the following channel parameters should be configured on the configuration page of the tool. The corresponding frequency is not displayed directly, you can follow CH0 For the center frequency of 2402, the mode of adding 1M to each channel number is manually calculated, the formula Fc = 2402 + k MHz, k = 0, 1, 2...,78

Figure 3. The frequency point of DUT tool channel CH 0 corresponds to 2402 settings.

For BLE only device testing, the corresponding relationship between the channel number of the DUT and the frequency of the WLAN Meter is that CH0 is the center frequency of 2402, and each channel number is calculated manually in the mode of adding 2M, the formula Fc = 2402 + k * 2 MHz, k = 0, 1, 2...,39

Figure 4. BLE's RF CH19 corresponds to 2440MHz frequency or BR's CH38 channel

In addition, it should be noted that there are labels for Data channel Index and Advertising channel index. Some chip tools use this index as the channel label. The test equipment mainly focuses on the actual working frequency of the DUT, so please correspond to the RF channel column The channel number or frequency point is the parameter basis, and the RF center frequency point is used as the setting parameter to set in the WLAN Meter software.

Figure 5. BLE channel division and mapping relationship

Figure 6. WLAN Meter test BLE_1M signal spectrum and time domain power diagram

All in all, the parameters of the test equipment (EUT) are based on the actual working frequency of the radio frequency signal, and the radio frequency mode of the input signal can be matched with different signal codes or protocol marks. The center frequency of the signal is set as the setting. If you encounter a Bluetooth test, after collecting the signal, you can only see the power in the Power graph, but you cannot see the frequency domain signal in the Spectrum graph. Remember to scroll to zoom the graph to see if the signal is in another position, because the WT-20x device can collect the signal The bandwidth exceeds 100MHz.