How to fix the interferences of coaxial wiring on mobile phone networks

January 9, 2019.


Since the 4G came up we are aware about how mobile phone networks affect television coaxial cable networks. But what happens when occurs exactly the opposite, when coax networks have an impact on mobile networks? Why does this happen? And if the problem is not solved, it is subject to a sanction?

Why coaxial wiring is likely to interfere in mobile networks?

First of all, coaxial wiring not only affects mobile phone networks. In fact they may have an impact on any service that is using the radiofrequency spectrum: Emergency services, radionavigation systems, amateur radio operators, etc.

Examples of bad practices and degraded installations
Examples of bad practices and degraded installations.

Poor executions, degraded elements… or installations that are nothing but a mess. All of them are situations that each and every aerial installer has had to deal with, and they have a negative impact in services that use the radiofrequency spectrum.

All these cases have a common denominator: The shielding of wiring, passive equipment or active equipment is of poor quality or is degraded and radiations are release from the cable itself. Other factors such as excessive ground impedance in the equipment can also play a part.

... anyway, the most common case is depicted below: A terrestrial and satellite amplifying station is radiating satellite frequencies (950 MHz) trough the Yagi antenna affecting communications in the 4G band. This happens because of low cost equipment, which uses poor quality filters (or not filters at all!) to keep price low.

Bad quality amplifying station has an impact on mobile phone bands
Bad quality amplifying station has an impact on mobile phone bands

Economic sanctions for improper installations

In Spain, the UNE 50083 standard is explicit about maximum radiation levels that are considered acceptable in coax wiring installations. What follows is an excerpt from the radiation limits as defined in the UNE50083-8:2002 standard:

FREQUENCY RANGEFIELD STRENGTH
(at 3 meters)
BANDWIDTH MEASUREMENT
From 5 to 30 MHz34 to 27 µV/m9 kHz
From 30 to 950 MHz27 µV/m120 kHz
From 950 to 2500 MHz50 µV/m1000 kHz
From 2500 to 3000 MHzz64 µV/m1000 kHz
Radiation limits determined in the UNE50083-8:2002 regulation (Spain)

In Spain, the General Law of Telecommunications specifies that “inspection, detection, location, identification and removal of harmful interferences, irregularities and disturbances in the telecommunications system are part of the administration, management and control of the spectrum , initiating the sanction procedure if required”.

Acording to regulation, that considers the spectrum as a public good, when an improper installation causes interferences in a spectrum band:

  • The first step is to contact the owner of the installation that is causing interferences to request its switch-off.
  • The owner will be advised to take proper actions in order to avoid the problem showing up again when the installation switches on again (in case the owner wants to do so).
  • The Government Administration will apply economic sanctions against the owner who, by omitting both points above, keeps causing damage by interferences of his installation.

Measuring the electromagnetic field strength with PROMAX analyzers

The installers using TV & Spectrum analyzers RANGER Neo or HD RANGER from PROMAX have the tools needed to check electromagnetic radiation thanks to the Field Strength function.

RANGER NEO ANALYZERS
Measuring electromagnetic field strength with PROMAX analyzers
Measuring electromagnetic field strength with PROMAX analyzers.

With a master aerial such as the AM-030 from PROMAX pointing to the unit that is suspected to be causing an interference can identify whether it is really irradiating an unwanted electromagnetic field or not. It is very important to properly configure the meter with the antenna K factor to obtain accurate measurements.

WATCH HOW TO USE THE FIELD STRENGTH FUNCTION

The K factor is the ratio between the electric field received by the antenna and the voltage generated at its output, which varies depending on reception frequency. The K factor table for each antenna shows this ratio according to the antenna operating frequency.

When the Field strength is being measured, the spectrum analyzer measures the level in dBµV/m (dB per 1 µV/m) using a 100 kHz filter. Signal and digital parameters identification functions are disabled because demodulation is not necessary. At the same time corrections from the K factor table are applied. This table must be previously loaded in the equipment.

Field strength measurement in a RANGER Neo TV and spectrum analyzer
Field strength measurement in a RANGER Neo TV and spectrum analyzer. The corrections calculated by the meter are displayed at the bottom of the screen.
RANGER NEO ANALYZERS
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PROMAX is a leading manufacturer of test and measurement systems, broadcast and TV signal distribution equipment. Our product lines include measuring instruments for cable TV, satellite TV, broadcast, wireless and fibre optics networks, FTTH and GPON analyzers. DVB-T modulators, IP streamers or IP converters (ASI, DVB-T) are among the company’s latest developments.