 Hello! In this video I will introduce you to the FCC certification requirements for Bluetooth low-energy devices and show you practical examples of RF measurements. All of these demonstrations are performed in conducted mode, but be aware that in fact most tests are performed in radiated mode. I hope this video helps you prepare your BLE device for true FCC certification. First I will briefly introduce you to the FCC requirements to understand the following matters. Next we will deal with the RF measurement of several parameters of the transmitted signal, understand reading the appropriate values and compare with the FCC requirements. Power spectral density is measured, which is the power distributed over unit of frequency band. Furthermore, the measurement of 6 dB bandwidth, which expresses whether the signal uses its occupied channel sufficiently. Similarly, 99 person bandwidth, which is only an auxiliary parameter. The RF output power of the signal and its purest emissions, these are any unwanted signals coming from the device, are also measured. Last but not least, the band edge is also determined which expresses whether the signal is sufficiently suppressed at the edges of the Bluetooth band, so to not interfere with other adjacent technologies. Now I will introduce you to the basic requirements set by the FCC for the evaluation of equipment transmitting in BLE technology. The FCC is the responsible body in the United States for implementing rules limiting the potential for interference to license operations by low-power non-license transmitters. These rules are included in FCC part 15 of title 47. The non-license device operated in band 2400 MHz to 2483.5 MHz must meet some of the following subparts of the regulation. It is part 15.247. It says the devices are limited to frequency hopping and digitally modulated scheme and part 15.249. This subpart doesn't impose restrictions on the modulation scheme or anti-application. The FCC classifies classic Bluetooth as a frequency hopping system. Nevertheless, Bluetooth or energy doesn't fulfill these requirements. Instead, the BLE is classified as digital modulation system in FCC. The device says must fulfill following requirements to the compliant with the FCC part 15.247. 6 dB bandwidth of the signal must be 500 kHz at least. Maximum permitted peak conducted output power is plus 30 dBm. Power spectral density conducted from the intentional radiator to the antenna should not be greater than 8 dBm measured in 3 kHz band during any time interval of continuous transmission. In any 100 kHz bandwidth outside the frequency band of operation the power shall be at least 20 dB below that in the 100 kHz bandwidth within the band that contains the highest level of the desired power. No matter if based on an RF conducted or a radiated measurement in peak mode. If the transmitter complies with the conducted power limits based on the use of arm averaging over a time interval the required attenuation shall be 30 dB instead of 20 dB. Attenuation below the general limit specified in 15.209 is not required but radiated harmonics and spurious emissions which falls within the restricted bands as defined in FCC part 15.205 must comply limits with the radiated emission specified in FCC part 15.209. Radiated harmonics and spurious emissions of devices complying with part 15.247 which fall within the restricted bands defined in FCC part 15.205 must also comply with the radiated emission limits specified in FCC part 15.209. Following table on the left hand side shows restricted bands defined in part 15.205 and the field strength of assessed emissions appearing within these frequency bands should not exceed the limits shown in table from FCC part 15.209 on right hand side. In this table are defined limits in a field strength and we probably will work with EIRP value. To determine the equivalent EIRP value we can use a formula below the table. Here are listed the basic parameters that are measured in the case of BLE technology at the FCC. These are exclusively transmitter parameters no specific requirements are defined for FCC compliance of the receiver. First a couple of remarks here it is important to set the input of the spectrum analyzer especially the input attenuator before each measurement. Although BLE usually doesn't have too much power it is still necessary to be aware of the risk of destroying the sensitive input of the analyzer. It is also necessary to set the signal display parameters correctly because incorrect configuration will lead to incorrect conclusions. All measurements will be made at one megabit per second but similarly can be applied to two megabit per second. Let's start with power spectral density. We will use a spectrum analyzer and measure in conducted mode. Measurements are performed on three channels low middle and high. The limit is plus 8 dBm over 3 kHz. We enter center frequency to 2400 megahertz and set the span to 1.5 megahertz rbw at 10 kHz sorry it could be 3 kHz vbw at 10 kHz. Detector on autopeak and trace on max hold. We place the marker at the maximum and read its value. We write down the results in a table and compare them with the limit. Of course we must not forget to add the value of the cable attenuation and the highest value of the antenna gain. We get the EIRP value. Now we focus on 6 dB bandwidth. The 6 dB bandwidth is defined as the difference between the upper and lower frequencies that are minus 6 dB relative to the peak. We use a spectrum analyzer and measure in conducted mode. Measurements are performed on three channels low middle and high. Once the signal has stabilized set the marker to the maximum amplitude level to read its value. Reduce this value by 6 dB and read the frequencies corresponding to the appropriate 6 dB points on the signal envelope. The 6 dB bandwidth limit is 500 kHz thus it means the bandwidth must be greater than 500 kHz. We enter center frequency at 2402 MHz resolution bandwidth to 100 kHz. View bandwidth to 300 kHz. Detector to autopeak and trace on max hold. To see the markers better we set the scale to 50 dB. We set a marker to peak value. Activate the occupied bandwidth feature. Let display the horizontal line which we set 6 dB lower compared to peak. It is on minus 4.24 dBM and using the power bandwidth function we then align the markers with the horizontal line and we get the value of occupied bandwidth. We write down the results in a table and compare them with the limit value of 500 kHz. As for 6 dB bandwidth we can measure the value for 99 person bandwidth. The measurement is performed on three channels low middle and high. The spectrum analyzer setting is the same as for the 6 dB bandwidth. We will activate the OBW function of our spectrum analyzer which will help us more easily to measure 99% bandwidth. There is no FCC limit for this parameter but for example for a very similar Canadian IC standard this parameter is measured. We enter center frequency to 2402 MHz, spent to 3 MHz, resolution bandwidth at 20 kHz, view bandwidth at 50 kHz, detector to outer peak and trace on max hold. Activate the occupied bandwidth feature and below we can see the value of occupied bandwidth. We put the measured values into the table again. Now I will show you the measurement of RFK output power. We will use a spectrum analyzer and measure in conducted mode. We will perform the measurements again on three channels. This time we set the RBW greater than or equal to 6 dB bandwidth. From this value we then derive span which must be at least three times larger than RBW similarly to VBW. This can be measured in case where the antenna has a gain of less than 6 dBi then the output power limit is defined to less than plus 40 dBm. We have a span at 3 MHz then we enter frequency to 2402 MHz, RBW at 1 MHz, VBW at 3 MHz. Detector to outer peak and trace on max hold. We simply place the marker to the maximum and read its value. We write down the results in a table and compare them with the limit. Of course we will not forget to add the value of cable attenuation and add the highest value of antenna gain. We get the EIRP value. We will now deal with unmounted radiation frequencies that arise as harmonics of the fundamental signal or as non-harmonic signals which arise for example as mixing products. FCC part 15.247 defines unwanted emissions as emissions that falls in non-restricted band and emissions that falls in a restricted band as defined in the 15.205. Emissions in not restricted band. FCC specifies if the maximum peak conducted output power procedure was used to demonstrate compliance of the fundamental emission output power then the peak output power measured in any 100 kHz band with outside of the authorized frequency band shall be attenuated by at least 20 dBi relative to the maximum in-band peak PSD level in 100 kHz. It means 20 dBi. If maximum conducted average output power was used to demonstrate compliance of the fundamental emission output power then the peak power in any 100 kHz bandwidth outside of the authorized frequency band shall be attenuated by at least 30 dBi relative to the maximum in-band peak PSD level in 100 kHz. It means 30 dBi. So the measurement is simple just to use peak marker to determine maximum amplitude level and to find out that all unwanted emissions are attenuated by at least minimum requirements. For the emissions in restricted frequency band these shall comply with the general radiated emission limits. Due to the emission limits are specified in radiated field strength levels so measurement performed to comply limits have relied on a radiated test configuration. However antenna port conducted measurements are also acceptable. We have to consider the attenuation of the cable maximum gain of antenna and so-called ground reflection factor which is 0 dBi for frequencies above 1 GHz. We will use a spectrum analyzer and measure in conducted mode although it should be noted that the FCC is measured in radiated mode. This also means among other things that the results may not correspond to the real measured value. The antenna connected to the device may not emit all the frequencies that come to it likewise due to the impedance adjustment to the RF trace there may be an undesirable deterioration of the levels. It is therefore important to keep in mind that the results from a certified laboratory having an adequate chamber may differ from yours. The measurement is performed on three frequencies. After the signal has stabilized we set the markers to all spectral lines that exceed or are close to the limit and for example we use the table view to read the values. For the restricted band we use RBW according to the frequency band. The limits are therefore different for different bands it will be further explained. Enter start frequency 30 MHz and stop frequency 26 GHz. Resolution band width at 100 kHz. View band width at 300 kHz. To have dynamics for reading let change the input attenuator to 10 dB. We put the detector to auto peak and trace on max hold and place markers in normal mode on each spectral lines so we can see the levels of individual spures. Even in this case it is necessary to add the attenuation of the cable and the antenna gain to measured value. We obtain the EIRP value which we can then compare with the limits. If a value is close to or even above the limit it is necessary to carefully evaluate whether the relevant frequency product actually meets the FCC requirements. Therefore we perform the evaluation with respect to the non-restricted band where since we measure in peak mode we subtract the value of 20 dB from the level of the carrier frequency and compare it with the levels of the measured spurs. In the case of restricted band we must compare these unwanted signals with an absolute level of minus 41 dBm which is the limits value for frequencies higher than 960 MHz. For lower frequencies relate the measured values to the field strength limits in FCC part 15.209. We can see from our table that both requirements are met for all unwanted frequencies. Here are examples of measured plots. We see that the levels meet the FCC limits. We will also focus on band edge measurement. This evaluates the transmitted signal from the point of view of interference into the band of neighboring technologies. We will use the marker delta method for gaining the values. This method can be used in case of continuous transmitting. With using a spectrum analyzer but we will only measure for the two outer channels. We measure maximum values in close proximity below and above the Bluetooth band so we find out what levels get out of the authorized band caused by a wanted signal. It is also necessary to evaluate this signal due to the attenuation of the cable and the gain of the antenna. In the case of conducted method the measurement can be performed as follows. Select the start and stop frequencies according to the used channel. In the case of the 2402 MHz frequency the span is from 2395 MHz to 2405 MHz. In the case of the 2480 MHz channel the span is from 2478.5 MHz to 2488.5 MHz. The display bandwidth is therefore always 10 MHz. After stabilizing the signal we set the marker to the maximum value of the signal envelope in the band up to 2400 MHz respectively in the band above 2483.5 MHz. We always compare this value with a minimum distance of 20 dB from the maximum in the authorized band. This measurement is also performed in radiated mode. The FCC sets the limits for radiated measurements in two bands. Lava band is 2300 to 2400 MHz and the higher band is 2480 to 2500 MHz. This maximum level measured at 3 meters from the device is 54 dB micro volts over meter for average measurement and or 74 dB micro volt meter per meter for peak measurement. We don't have the possibility of measuring in radiated mode but we can convert these values to the antenna input. Then 54 dB micro volt over meter for average corresponds to minus 41.23 dBm and 74 dB micro volts over meter for peak corresponds to minus 21.23 dBm. At the same time the signal measured in 100 kHz must be attenuated by at least 20 dB compared to the signal in the Bluetooth band. Measurements are performed for RBW equal to 1 MHz and VBW equal to 3 MHz and be careful it is necessary to take into account the requirements of restricted bands. So these are the bands 2310 to 2390 MHz and 2483.5 to 2500 MHz where the value must not exceed 500 micro volt over meter in distance of 3 meters. It means minus 41 dBm converted to the antenna. I also took this limit into account when evaluating the results. We have RBW at 100 kHz and VBW at 300 kHz. Enter star frequency to 2483.5 MHz and stop frequency to 2488.5 MHz. Detector on auto peak and trace on max hold. We find a peak in this subband using a marker and add another marker to the 2483.5 MHz as limit frequency. Now we change the start frequency to 2478.5 MHz so that we can also evaluate the attenuation against the wanted signal. In this moment we can also quickly check the measurement in average mode. We set the trace to clear bright and detector to average and again we put it in max hold. We have to find the maximum again so we change the start frequency to 2483.5 MHz. We put the marker 1 on peak and marker 2 back on 2483.5 MHz. To show the wanted signal in the display band set the start frequency to 2478.5 MHz. Here are examples of bandage measurement for all edges of the band. So how to evaluate the measured plots? In the region below the band we found the maximum value up to 2400 MHz and the maximum value above 2483.5 MHz. After taking into account the attenuation of the cable and the antenna gain we reach the average and peak values which we compare them with the limit of minus 41 dBm. And that's all for this session. Thank you for watching, hope you enjoyed the video and see you next time. Bye!