Why don't OFFEL antennas have the LTE filter integrated?
OFFEL chose to redesign all its antennas, suitable for the reception of UHF signals, based on the new working band E21÷E60, achieving side lobes with higher performances and a higher gain than those who would have gotten with the simple insertion of a LTE filter within the existing models. Excellent results have been obtained with these new antennas also thanks to the even more protection against the echoes.
What does "echo" mean?
An echo, also called multiple path, is an interference due to the reflection of the right signal on buildings, stretchs of water, mountains, obstacles, etc. that, because of the wider path, reaches the antenna later than the right signal. If the echo delay is lower than the guard interval and its level is at least 12/15 dB lower than the right signal level, it doesn't interfere with the right signal.
Instead, if the echo delay is higher than the guard interval, it has to be considered a disturbance like any other interfering signal. To know how to avoid the problems caused by the echoes see FAQ. A.3.
What kind of antenna assure the best protection against the echoes?
In order to ensure an adequate protection against the echoes it's necessary to use antennas with a great gain and very efficient side lobes.
Some examples can be art. 21-276 K47Z and art. 21-374B SPEED+ 47Z HD BIANCA.
What are the best antennas to receive RAI channels?
Since all the RAI channels are distributed on channels belonging to the band 4 , it is good practice to use an antenna capable of receiving frequencies between the channel E21 and the channel E40, which has a higher gain and more efficient side lobes than an UHF antenna (E21 ÷ E60) with the same elements.
The most recommended models for this purpose are the following articles: 21-435B SUN+ 15P HD BIANCA, 21-272 K47B and 21-371B SPEED+ 35B HD BIANCA.
When the RAI 1 mux is distributed in band 3, it's also recommended the use of art. 21-094B E5/E12Y6 BIANCA.
Why should I use a COMBI antenna instead of a log periodic one?
Compared to the log periodic antennas, the COMBI Z HD antennas are characterized by a higher directivity and a higher gain in the UHF band, as well as by a greater mechanical strength. The COMBI Z HD antennas offer greater performances also from the point of view of protection against LTE signals.
How can I improve the quality of a DTT signal?
The highest quality of a signal is obtained at the output of the dipole antenna. Outside of the antenna itself, there are no components (e.g. amplifiers, filters, traps, etc.) that can improve the quality of a signal. To improve the quality of a channel you can try to use an antenna with multiple elements (more directive), or an antenna that has among its characteristics very efficient side lobes.
A technique that gives excellent results on the DTT signals is the coupling of two antennas.