C Band and 5G Interference

C Band and 5G Interference

Introduction and History of C Band Interference in Australia

C Band satellite operators and users have faced a number of challenges in recent years as the radio frequency spectrum has become increasingly congested by the insatiable demand for bandwidth (MHz) by mobile (also referred to as ‘cellular’) terrestrial service operators. Many satellite users of C Band will have noticed 5G mobile services beginning operations in their local areas and the subsequent degradation and denial of C Band satellite signals (3.7-4.2GHz).

The story of C Band Interference in Australia begins in October 2000 when the Australian Media and Communication Authority (ACMA) auctioned off frequency bands at the lower end of C Band, 3.425-3.575GHz for terrestrial service providers.

Most recently in 2018, ACMA auctioned off 125MHz of spectrum in the extended C Band 3.575 – 3.7GHz (3.6GHz) for the use of 5G mobile services, raising approximately A$853 million for the Government’s coffers.

As such, operators and users of C Band are now experiencing severe degradation and denial of C Band satellite services and are having to contend with terrestrial services operating on frequencies much closer to the remaining operational C Band frequency block (3.7-4.2GHz).

Full details of ACMA’s 3.6GHz auction are available here.

Why is 5G degrading my C Band Satellite reception?

The nature of terrestrial mobile services is such that their base stations transmit much higher power levels compared to signals received from satellites in geostationary orbit.

This means that despite 5G services being transmitted on slightly different frequencies to that of C Band, satellite services are severely degraded by the much greater signal level transmitted by 5G base stations due to signal overload. As an analogy, consider having a conversation with someone standing next to you at a music concert. It’s difficult to hear them. In much the same way, C Band satellite reception equipment is simply overwhelmed by the noise and is driven into compression, degrading and denying the use of C Band for satellite services.

The impact of 5G is further compounded by its technology architecture that relies on deploying many base stations in order to concentrate coverage and ensure optimum 5G coverage in urban areas.

The Importance of a Site Survey

An unfortunate by-product of the wireless age is microwave interference. Microwaves sources can interfere with satellite TV reception because they operate on similar frequencies to those used by international satellites. Areas such as roof tops are exposed to high levels of microwave signals making satellite receiving systems extremely susceptible to C Band satellite interference where there are no buildings or trees to shield them.

To minimise the effect of interference a site survey is necessary. A spectrum analyser should be used to measure any terrestrial interference. A small test dish should be set up with an identical LNB to the one supplied with the system, and should be used to test for any interference. If interference is detected, then the user should be advised of the increased systems costs involved in ensuring the reliable performance of the system after it is commissioned.

Further, it should be noted that not all receivers, LNBs, cables and dishes are of equal quality and capacity, and all have different interference endurance characteristics. Thus, it is of absolute importance that a site survey is conducted to ensure the best combination of equipment is used to mitigate interference issues and optimise the system’s long-term reliability and performance.

The Input Frequency Solution (Major Interference Cases)

The ultimate solution is to eliminate the 5G interfering signal before it enters the LNB in the first place.

This can be done in two ways:

Fig. 1 – Install Av-Comm’s range of C Band LNBs with inbuilt Bandpass Filters.

Fig. 2 – Install a standalone Waveguide Filter which is placed between the Feedhorn and the input of the LNB.

These solutions offer the highest rates of success, by providing up to 75dB of protection against 5G interference. In the most severe cases, a filtered LNB and a standalone Waveguide Filter can be used together to offer the ultimate protection against any interference.

It should be noted that standalone Waveguide Filters create insertion loss which may be unacceptable, depending on the link budget information specific to the downlink site. The insertion loss of a typical standalone Waveguide Filter will result in a carrier to noise (C/N) reduction by ~0.5-1.0dB.

Over the past decade Av-Comm has developed a range of C Band LNBs with inbuilt Bandpass Filters to solve out of band interference cases. Av-Comm’s preferred method to eliminate C Band interference, is to use an LNB with inbuilt Bandpass Filter. We believe this approach is optimal because unlike standalone Waveguide Filters, Av-Comm’s filtered LNB solutions do not suffer from insertion loss and provide a more cost effective solution.

The table overleaf shows the specifications on our LNB and waveguide filter range, full specification sheets along with frequency plots are available on request. High stability (5Khz) versions of all LNBs are also available for improved reception of MPEG4 signals.

Fig. 1

Fig. 2

Av-Comm C Band Filtered LNB Interference Solutions

PARAMETERVALUEVALUEVALUEVALUE
Cat. NumberL1516L1517L1510L1512
Input Frequency3.7 – 4.2 GHz3.625 – 4.2 GHz3.625 – 4.2 GHz3.7 – 4.2 GHz
Filter TypeBandpass Filter
(3.7 – 4.2 GHz)
Bandpass Filter
(3.625–4.2GHz)
Bandpass Filter (3.625 – 4.2 GHz)Bandpass Filter
(3.7 – 4.2 GHz)
Noise Temperature25 K25K25K25K
Local Oscillator5.150 GHz5.150 GHz5.150 GHz5.150 GHz
Local Oscillator Stability+ / – 300 kHz+ / – 300 kHz+ / – 5 kHz+ / – 5 kHz
Local Oscillator TypePLLPLLPLLPLL
Output ConnectorF-Type 75 ΩF-Type 75 ΩF-Type 75 ΩF-Type 75 Ω
PARAMETERVALUEVALUEVALUEVALUE
Cat. NumberL1521L1522L1507L1508
Input Frequency3.9 – 4.2 GHz3.8 – 4.2 GHz3.8 – 4.2 GHz3.9 – 4.2 GHz
Filter TypeBandpass Filter
(3.9 – 4.2 GHz)
Bandpass Filter
(3.8–4.2GHz)
Bandpass Filter
(3.8 – 4.2 GHz)
Bandpass Filter
(3.9 – 4.2 GHz)
Noise Temperature25 K25K25K25K
Local Oscillator5.150 GHz5.150 GHz5.150 GHz5.150 GHz
Local Oscillator Stability+ / – 300 kHz+ / – 300 kHz+ / – 5 kHz+ / – 5 kHz
Local Oscillator TypePLLPLLPLLPLL
Output ConnectorF-Type 75 ΩF-Type 75 ΩF-Type 75 ΩF-Type 75 Ω

The Inline Solution (Minor Interference Cases)

Sites suffering from relatively minor cases of 5G interference, can achieve some relief through the addition of an inline L Band Filter. These filters are designed to pass a desirable block of frequencies through the coax cable and into the decoder or modem, actively filtering undesired signals to the stop band.

Inline L Band Filters provide rejection of unwanted 5G interference signals after frequency conversion has taken place in the LNB, thus only providing rejection of low-level interference generating by mixing within the LNB (i.e. lower than the LNBs P1 compression point) or L Band interference entering through the coax cable.

A satellite receiver or modem is designed to accept an ~500MHz wide range of input signals, and, as such, does not have any great selectivity. Furthermore, satellite receiver and modems are designed to accept signals of a certain signal strength,(typically -25 to -65dBm). Inline L Band Filters improve reception by ensuring any undesirable signals greater in signal level than the satellite decoder or modem is designed to receive, do not enter the tuner and drive it into compression.

Av-Comm has designed several inline L Band  Filters as part of our C Band interference solution product range, which will eliminate interference that is passed by the LNB and that does not drive the LNB into compression. Av-Comm’s proprietary inline L Band Filter range is the first recommended step in fixing interference problems in existing systems.

The table below shows the specification of Av-Comm’s range of inline L Band Filters, a full datasheet along with frequency plot is available for each model, on request.

PARAMETERVALUEVALUEVALUEVALUE
Cat. NumberF4002F4004F4006F4008
PassBand950-1530 MHz950-1450 MHz950-1350 MHz950-1250 MHz
StopBand1610-1830 MHz1530-1750 MHz1430-1650 MHz1330-1550 MHz
Rejection>45dB>45dB>45dB>45dB
Filter Type
Low Pass FilterLow Pass FilterLow Pass FilterLow Pass Filter
Connector TypeF-Type 75 ΩF-Type 75 ΩF-Type 75 ΩF-Type 75 Ω

Feedhorn Solutions

Av-Comm has also developed a range of feedhorns that work to maximise the illumination of the dish and provide superior isolation from interfering signals.

Av-Comm has developed the F1341 high-efficiency feedring to optimise the illumination of the dish surface and minimise the feedhorn’s susceptibility to signals emanating from other terrestrial sources adjacent to the satellite dish. We fit our F1341 high efficiency feedring to all C Band systems to typically provide a Carrier to Noise ratio increase of 0.2-1.0dB, depending on the surface accuracy of the dish.

Av-Comm has also recently developed the F1750 C Band orthomode coupler (OMT) using the direct-port coupling technique instead of the more common mutual coupling technique.

We have discovered that by using the direct-port coupling technique we are able to provide increased isolation between the two ports of the OMT coupler. All of these small increases in performance and isolation help to provide a whole system solution that effectively minimises the impact of out-of-band C Band interference.

C Band Single Polarity Feedhorn

C Band Single Polarity Feedhorn
Cat. NumberF1300
Input Frequency Range3.4 – 4.2 GHz
LNB FlangeCPR-229
Feed Strut ConfigurationTri or Quad

C Band High Efficiency Feedring

C Band High Efficiency Feedhorn
Cat. NumberF1341
Input Frequency Range3.4 – 4.2 GHz
Feed Strut ConfigurationTri or Quad

C Band OMT Coupler (Ortho Mode Transducer)

C Band OMT Coupler
Cat. NumberF1750
Input Frequency Range3.4 – 4.2 GHz
LNB FlangeCPR-229
VSWR1.44 typ.
PolarisationLinear

C Band High Efficiency Feedhorn and OMT

Cat. NumberF1751
Input Frequency3.4 – 4.2 GHz
LNB FlangeCPR-229
PolarisationLinear
Feed Strut ConfigurationTri or Quad
Isolation30dB typ.

F1341+F1750 C Band OMT

F1341+F1750 in single polarity configuration

RECOMMENDATIONS

Av-Comm recommends that where interference is encountered, technicians should try the simplest solutions first, working through the mitigation techniques described in this guide  to achieve the best interference reduction solution for the specific system at hand. In the case of existing systems or minor cases of 5G interference, if it is possible to still receive some satellite channels, it is likely that some of the simpler solutions suggested in this guide will resolve the interference issue to restore normal performance.

The location of your satellite dish can be a significant factor impacting reception of C Band satellite signals. Ideally, satellite dishes should be mounted on the ground level away from elevated sources of interference, using buildings or natural barriers to shield the dish from known sources of interfering signals. It should be noted that interference is likely to be more severe when receiving satellites that have a low look angle, although this does not preclude interference on dishes set to high elevation values. Relocation of a satellite dish to a more protected area is a practical last resort option.

However, in severe cases of terrestrial interference, satellite signals in the 3.4-3.7GHz range will be lost, due to the close frequency proximity of interfering 5G terrestrial signals. Furthermore,  normal performance for signals in the 3.7-3.8GHz band is unlikely, due to the real world roll off characteristics of bandpass filters (waveguide, LNB, Inline). Av-Comm recommends using our Av-Comm C Bandpass Filtered LNBs to provide optimal protection from 5G interference sources. In severe cases a Standalone Waveguide Filter can be added to provide additional rejection of interfering signals (Note: standalone waveguide filters create insertion loss). In extreme cases where reception of a frequency is mission critical, Av-Comm can design a custom Standalone Waveguide Filter to pass only a single satellite carrier.

If the interfering carrier is close to the desired satellite frequency, an LNB with the filter roll-off characteristic close to or marginally overlapping the desired frequency should be selected. Figure 3 shows the frequencies allocated by the ACMA to the four operators with 5G/C Band spectrum rights in capital and regional cities. Operators will begin providing commercial services from Q1 2020 with limited testing permitted from mid 2019.

Which LNB do I need?

Looking at Figure 3 it can be seen that depending on the location, and the frequency band allocated to the operator in that area, different Av-Comm LNBs will be required to receive satellite signals. For example, if the satellite dish is located in Melbourne and the local operator is Dense Air, the interference sources will be 3695-3700MHz. This means that any satellite signal below 3.7GHz will be impossible to receive satisfactorily and any satellite signal above 3.8GHz will have some chance. In this example Av-Comm would recommend our L1522 or L1521 LNBs to provide optimal reception of the unaffected portion of C Band, filtering out the 5G interference source.

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