What is interesting is that all CAT3 ops use a RADALT so the airline business should be extremely worried, but don’t seem to be.
Airborne_Again wrote:
Then what is the problem? That the 5G networks transmit outside their assigned bands?
You can get problems from adjacent bands even with no transmission out of band (receivers can be desensitised) especially if the transmission is high power. Sufficiently good filtering should stop that from being a problem, though, and 5G is typically run at very low powers (5G cells tend to be very small).
Many thanks. This leads to the question of whether this is a real issue (the FAA says there have been no reported incidents) or whether somebody has actually determined that the above compliance spec is unsufficient.
It may be a bit like the old “FM Immunity” issue which caused a huge amount of expense but AFAIK nobody ever demonstrated a problem with any equipment in actual use.
Peter wrote:
I wondered the same. What is needed is a post longer than 1.5 lines, but we aren’t going to get one
Here’s the full text:
RTCA DO-160 – Section 20.0 – Radio Frequency Susceptibility (Radiated and Conducted)
These tests determine whether equipment will operate within performance specifications when the equipment and its interconnecting wiring are exposed to a level of RF modulated power, either by a radiated RF field or by injection probe induction onto the power lines and interface circuit wiring.
Two test procedures are used:
From 10 kHz to 400 MHz, the equipment under test (EUT) is subjected to RF signals coupled by means of injection probes into its cable bundles, and
for frequencies between 100 MHz and the upper frequency limit, the EUT is subjected to radiated RF fields. There is an intentional overlap of the tests from 100 to 400 MHz.
Radiated susceptibility tests from 100 MHz to 18 GHz may be conducted using methods and materials as described within Section 20.5 (Anechoic Chamber Method) or Section 20.6 (Reverberation Chamber Method). The choice of methods is at the discretion of the applicant.
Equipment with special signal, frequency, modulation or bandpass characteristics may require test variations as specified by the applicable performance standards.
The result of these tests can be used to:
Determine equipment response to various RF threats such as HIRF, T-PEDs, and
installed system’s emissions, and to
Permit categories to be assigned defining the conducted and radiated RF test levels of
the equipment
These tests are sufficient to obtain environmental qualification for radio frequency susceptibility of the equipment. Additional tests may be necessary to certify the installation of systems in an aircraft dependent on the functions performed.
Categories B, D, F, G, L, M and O provide test levels which directly relate to the high intensity radiated field (HIRF) external field environments for systems with highest criticality as specified in the HIRF regulations.
Category R provides test levels for equipment when: a) Bench testing is allowed to meet the HIRF for systems with high criticality as specified in the HIRF regulations, and b) Showing backdoor Transmitting-Portable Electronic Device (T-PED) tolerance.
Category S provides a minimum test level where aircraft effects from the external electromagnetic environment are minor and where interference free operation on the aircraft is desirable but not required. This category may also be representative of the internal EMI environment from aircraft equipment.
Category T provides test levels for equipment when bench testing is allowed to meet the HIRF for systems with moderate criticality as specified in the HIRF regulations. This category may also be representative of the internal EMI environment from aircraft equipment.
Categories W and Y a) Bench testing supporting compliance to HIRF Special Conditions, and provide test levels for: b) Showing backdoor T-PED tolerance
Category Q indicates tests conducted at test limits or with modulations other than those specified in these procedures.
I wondered the same. What is needed is a post longer than 1.5 lines, but we aren’t going to get one 
Probably the issue is that any RADALT design in current mfg was done in the 1980s. The famous KRA10 certainly was:
wigglyamp wrote:
The TSO does require compliance with the environmental qualification requirements in DO-160D or later. This has sections covering the susceptibility of the devices to differing emission sources.
Then what is the problem? That the 5G networks transmit outside their assigned bands?
Airborne_Again wrote:
Isn’t it a bit strange that a TSO does not consider the effect of transmissions on adjacent bands? That sounds like inviting problems.
The TSO does require compliance with the environmental qualification requirements in DO-160D or later. This has sections covering the susceptibility of the devices to differing emission sources.
Radio altimeters operate between 4200-4400 MHz. Currently, the FAA’s approval process for radar altimeters is based on FAA Technical Standard Order TSO-C87A, Airborne Low-Range Radio Altimeter. TSO-C87A does not provide criteria for compatibility with adjacent band operations, including potential impacts associated with wireless communications system deployments.
Isn’t it a bit strange that a TSO does not consider the effect of transmissions on adjacent bands? That sounds like inviting problems.
It’s related to 5G network using the 3.7-3.9GHz band.
Radio altimeters affected by wireless broadband networks in the 3700-3980 MHz bands
For the past 15 years, the 3 GHz band globally has been the subject of harmonization activity for mobile broadband, both at the International Telecommunication Union and within regional groups. A number of countries already have allocated and assigned spectrum for wireless deployments in the 3 GHz range and additional countries are following suit. Many countries around the world are already deploying wireless networks in the bands from 3300-4200 MHz; some countries have implemented temporary technical, regulatory and operational mitigations, including temporary proximity and power restrictions, on wireless broadband networks operating in bands ranging from 3700-4200 MHz. There have not yet been proven reports of harmful interference due to wireless broadband operations internationally, although this issue is continuing to be studied. In the United States, there has been wireless broadband deployment in the 3.65-3.7 GHz band since 2007. The FCC started a proceeding to authorize mobile broadband service in the 3.55-3.7 GHz band in December 2012 and adopted final rules in April 2015 and October 2018. Commercial deployment started in September 2019, with no known issues for altimeters to date.
Where are these 3.7-3.9GHz networks and what are they?
