Mobile operators, both national and overseas and current LTE deployment trials identify two different conditions which may cause interferences:
1. HEAD/END EQUIPMENT AFFECTED BY MOBILE TRANSMITTERS (BTS). Or in other words, being affected by the downlink. Equipment updated to the latest frequency plan (C21-C59) or anti-LTE filters shall be used to protect against these signals.
2. INTERFERENCES ON DVB-T EQUIPMENT CUASE BY MOBILE TERMINALS (Or being affected by the uplink). Improve the shielding in the coaxial cable, connectorization and/or use of anti-LTE filters.
Filters are the main characters in this Digital Dividend, whether if it’s the headend that is being affected or not. In fact, one usual applications of these filters is to adapt the coaxial network to the new operational frequencies.
We can classify the filter’s applications or use in:
Prevention: Previous to harmful signals, carried on at the same time at the Headend’s frequencies migration.
Mitigacion: Where it is already an interference affecting the installation.
Adaptation de la red de TV a los nuevos requisitos: el filtro limita la banda de TV a las nuevas frecuencias establecidas.
Having in mind that we need these filters for more than to eliminate interferences, their features, particularly in the case of H/Es affected by BTS, shall be precise enough not to modify the TV frequency band. This accuracy needs also not to be affected by environmental conditions.
Choosing the filter
When choosing a filter, we need to evaluate up to 3 different criteria: location, DTT frequencies and degree of affectation due to present LTE signals.
Location: depending on the type of H/E used, the filter shall be installed in the mast, at the amplifier or in every user outlet. The installer shall identify which elements need to be protected against LTE.
Frequency bands: When possible, it is recommended to use filter with the lowest frequency cut off to maintain LTE interferences away.
Degree of affectation: he important key here is the signal strenght different between DTT and LTE signals. The more similar they are, the more rejection we will need. If the difference is bigger than 10 dB, rejection shouldn’t be as determinant.
The cheating filtering graphs
It seems reasonable to think that the frequency response is the key feature of a filter. It even seems reasonable to think that rejection is also a primordial fact.
But we should think twice since, although rejection is quite important, its relevance will highly depend on the interferent signal. In other words, it’s worthless to use a 50dB rejetion filter in the uplink band if the interfering signals depend on other circumstances, such as not being generated from a BTS or that the entry point of the unwanted signal is not at the headend. Filters for H/E equipment are designed to eliminate interferences from the Downlink and leave its operating band as intact as possible.
Televes’ LTE filters offer a whole range of possibilities: variable rejection at channels 58, 59 or 60. From high stability microcavities filters to LC filter for those less exigent scenarios
Using our Televes’ guide “Filters to prevent and mitigate LTE effects”, installers will ensure a sucessful solution for any installation