Recently, the accelerated 5G cellular network rollout in the Asia-Pacific region has speeded up the installation and use of 5G rejection bandpass filters (BPF) for satellite television receive-only (TVRO) antenna systems. In Hong Kong alone, more than one thousand C-band TVRO antenna systems or satellite master antenna television (SMATV) systems need to be upgraded with 5G rejection BPF, where a great portion of the antennas will be upgraded using AsiaSat’s 5G filters.
AsiaSat 5G rejection BPF has been put on the market since 2019 and has been well received in the satellite TV community. With its compact profile, light weight and excellent 5G rejection performance, the BPF has become an essential component for a C-band satellite reception site.
This paper summarises what we have learned from troubleshooting a problem involving BPF installation. Since the quality standard of the BPF installation could significantly impact the 5G rejection filter’s performance and hence the satellite-TV’s user experience, we are sharing this experience in order to provide some diagnosis guidelines that may be helpful for BPF installation.
2. A Real 5G Rejection BPF Installation Troubleshooting Case
One of our customers has reported that a recently installed 5G BPF did not function as expected – interference still occurred intermittently and impaired the satellite TV reception. The spectrum plots before and after BPF installation are shown in Figure 1(a) and (b).
It can be seen from Figure 1(a) that there was intensive 5G interference at around 3430 MHz, with a bandwidth of about 60 MHz. After the BPF installation, interference was reduced by only 20 dB, as shown in Figure 1(b), performing at a far lower level than the > 60 dB rejection level that AsiaSat BPF-3700S filter was designed to provide. The 5G interference to the TVRO system remained strong and “robbed” the satellite carrier power from the low noise block-downconverter (LNB), putting up mosaics on the TV screen.
2.1 Symptoms and the Preliminary Diagnosis
We started by asking our customer to describe the operational environment as well as the connection status of the equipment, e.g. the antenna feed horn, the BPF and the LNB.
According to the customer, no 5G base station shared the same rooftop with the satellite dish – which could have been the case for many buildings in Hong Kong. We were also told that there were no 5G base stations in the pointing direction of the satellite dish. In other words, there was no known reason why the 5G interference power would exceed the design limit of the 5G rejection BPF.
The customer sent us a close-up photo showing the connection on the TVRO equipment which is shown in Figure 2(a). It was a front-fed TVRO, and the Type-A LNB used by the customer was of a light-weight type secured by four screws and has a non-standard waveguide interface. The LNB was enclosed in a plastic shell and appeared not to be fully EMI-shielded.
For the sake of comparison and in an attempt to mitigate the problem, we asked the customer to repeat the spectrum measurement using a Type-B LNB with a full-metallic body and standard WR229 input interface. Figure 2(b) shows the hardware connection of the Type-B LNB, where 10 screws were used to secure the BPF. Unfortunately, there was no improvement in the level of 5G interference at the Type-B LNB’s output.
The spectrum plots comparison is shown in Figure 3.