Shanghai Interactive Television Co. Ltd. (SiTV), under the Shanghai Media Group (SMG) and engaged in digital TV and video on demand businesses, is a user on AsiaSat 6 distributing 16 HDTV channels across China.
A 2.4m antenna at SMG monitoring site, locating at Shanghai’s Yangpu district, experienced a strong unknown interference, which led to severe pixelation and complete blackout of its reception as shown in Figure 1 below:
Figure 1. TV monitors in red boxes displaying channels being affected by interference – monitor in top right corner shows pixelation and the bottom two experience complete black out
At SMG’s invitation, AsiaSat conducted an on-site troubleshooting together with SMG engineers. Based on the spectrum plots and the existence of two 5G base stations nearby, the issue was expected to be originated from a typical 5G signal interference. The spectrum plot as shown in Figure 2 below indicated a major signal interference within the 3400-3600 MHz range, with the strongest interference at 3550 MHz, the frequency band for 5G in China.
Figure 2. V-pol spectrum plot, with apparent interference between 3400-3600 MHz range, and strongest interference at 3550 MHz
According to link budget analysis, using a 2.4m antenna to receive HD signals from a satellite transmitting at a downlink EIRP of 40 dBW and Modcod QPSK ¾, the link margin would be about 5 dB under normal condition. However, the actual observed interference signal was transmitting at much higher power, which was sufficient to create a saturation type of interference, thus causing degradation of picture quality or even screen black out.
After the root cause was identified, AsiaSat provided its self developed 5G bandpass filter (BPF) for SMG to install onto the H-pol output of its 2.4m antenna.
Figure 3. AsiaSat BPF installed onto the H-pol output of the antenna
Results after installing the bandpass filter: Comparison of the two spectrum plots before and after BPF installation is shown below. Figure 4(a) – H-pol spectrum plot before installing bandpass filter, Figure 4(b) – H-pol spectrum plot after installing bandpass filter, showing the reception of TV signals has resumed normal.
Figure 4(a) H-pol spectrum plot before installing BPF, pink marked area refers to the power of signal
Figure 4(b) H-pol spectrum plot after installing BPF, showing interfering signal has been filtered
The pre-LNB microwave BPF solution is the most cost-effective measure to mitigate 5G saturation interference by far. Despite affected by multiple interfering sources and interfering base stations as close as 100m, the AsiaSat BPF still functions effectively, ensuring signal reception remains unaffected.
Figure 5. The 2.4m antenna installed with AsiaSat’s bandpass filters to reject 5G interference