FAQ: Antennas
FAQ A.1
Why don't OFFEL antennas have the 4G or 5G filter integrated?
OFFEL chose to redesign all its antennas, suitable for the reception of UHF signals (Z HD series: channels E21÷E60; 5G series: channels 21÷E48), achieving side lobes with higher performances and a higher gain than those who would have gotten with the simple insertion of a filter for mobile signals within the existing models. Excellent results are obtained with these antennas also thanks to the even more protection against the echoes.
UHF antennas
Multiband antennas
FAQ A.2
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.
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 (channels E21÷E60) or art. 21-277 K47 5G (channels E21÷E48)and art. 21-374B SPEED+ 47Z HD BIANCA or art. 21-375B SPEED+ 43 5G BIANCA.
FAQ A.4
Which antenna should I use to receive RAI channels?
In areas where RAI programs are received within channel E40 (i.e. on channels E26, E30, E40 or E26, E37, E40 or E27, E37, E40), 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÷E48) 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.
Instead, in areas where RAI programs are received beyond channel E40 (i.e. on channels E26, E40, E43 or E26, E40, E45) it is better to use an antenna capable of receiving frequencies between the channel E21 and the channel E48.
The most recommended models for this purpose are the following articles: 21-440B SUN + 15 5G BIANCA, 21-277 K47 5G and 21-375B SPEED + 43 5G BIANCA.
FAQ A.5
Why should I use a COMBI antenna instead of a log periodic one?
Both the logarithmic antennas and the antennas of the COMBI series are multi-band antennas, or antennas designed to receive multiple bands simultaneously (e.g. VHF and UHF). These antennas are made in such a way that a part of elements is dedicated to the reception of a band and another part of elements is dedicated to the reception of the other band.
Compared to the log periodic antennas, the COMBI 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 antennas offer greater performances also from the point of view of protection against LTE signals.
FAQ A.6
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.
FAQ A.7
What is meant by coupling two UHF antennas?
The coupling of two antennas is carried out in order to increase the directivity and reduce the reception disturbances caused by possible multiple paths (echoes) or by isofrequency channels coming from different directions with respect to the main reception one, or to stabilize any unevenness caused from fading. Thanks to the coupling it is possible to restrict the reception lobe of the antennas and to cause the disturbance signal to fall into a so-called "zero" point, ie a point of the reception lobe characterized by a high attenuation.
There are different types of coupling:
● horizontal coupling, useful if the disturbance is lateral;
● vertical coupling, to counteract a disturbance coming from the bottom;
● staggered vertical coupling, in case of disturbance coming from the back (i.e. disturbance and useful signal form an angle of 180°).
The coupling is achieved by placing two (equal) parallel antennas side by side on the same plane (horizontal or vertical) and connecting them to a coupler for two antennas with two perfectly equal cables (both for the type of cable and for the length).
For the coupling to be effective, the two antennas must be installed at the optimal distance, which is calculated taking into account the angle between the useful signal and the disturbance signal and the wavelength of the television channel to be received.
If you need to receive the channels of the entire UHF band, it is advisable to use antennas with at least 15 elements, even better if more direct antennas are used.
