This article presents the actual measurement results and how to configure the channel amplifier in the implementation of a SMATV system of DVB-T2 terrestrial television for about 70 terminal outlets. Due to specific reception conditions (2 transmitters, with the more powerful one closer and the less powerful farther away) the antenna set was based on DIPOL SMART series antennas.
The basic functions of the ST-6986, the latest in the Signal line of meters, were used for the measurements. The options used included the measurement of signal power, modulation error ratio MER and frequency spectrum imaging function in the UHF band.
The final result of the work was an equal signal level for the required frequencies at the output of the amplifier. The following images show the final frequency spectrum of the signals of the amplifier and the signal meter. The following part of the article describes the step-by-step approach to this stage.
Frequency spectrum in Terra channel amplifier
Frequency spectrum in the Signal meter
- reception of 5 DVB-T/DVB-T2 multiplexes from two transmitters. 4 multiplexes from a local 100 kW transmitter (a distance of 12 km), 1 multiplex from a 50 kW transmitter 50 km away.
- distribution of signals in a SMATV system of about 70 receivers.
- using an antenna set consisting of two DIPOL SMART antennas: the CITY model for local reception, the HORIZON model for reception from a distant transmitter,
- the CITY antenna operating in passive mode, the HORIZON antenna, depending on the parameters of the received signal, operating in passive or active mode,
- using a TERRA PA420T channel amplifier to equalize the signal level for all multiplexes and distribute the signal in a SMATV system.
Equipment used during the installation
- Dipol SMART City A2010 antenna
- Dipol SMART Horizon A2230 antenna
- Terra PA420T R82516 channel amplifier
- Signal ST-6986 R10210 signal meter
DIPOL SMART CITY antenna A2010
DIPOL SMART HORIZON antenna A2230
Terra PA420T channel amplifier R82516
Schematic diagram of the system
Transmitter no. 1 – distance 12 km, power 100 kW:
- channel 21 (474 MHz) MUX4,
- channel 22 (482 MHz) MUX3,
- channel 25 (506 MHz) MUX TVP,
- channel 43 (650 MHz) MUX 1.
Transmitter no. 2 – distance 50 km, power 50 kW:
- channel 36 (594 MHz) MUX 2.
Due to the short distance of the reception site from the powerful transmitter, a DIPOL SMART CITY A2010
antenna operating in passive mode was used to receive channels from the no. 1 transmitter. The results of measurements made with the Signal ST-6986 R10510
meter are shown in the screenshots below:
Receiving parameters are very good. For DVB-T2 multiplexes (channels: 21, 25, 43) an identical MER modulation error rate of 32.4 dB was obtained. For the DVB-T multiplex (channel 22), the MER value was 30.1 dB. In both cases, the obtained values are a guarantee of correct reception. The power of the received signal averaged 70 dBuV, which also provides a large margin of safety for reception.
When setting the CITY antenna to the no. 1 transmitter, reception of MUX 2 (channel 36) from the no. 2 transmitter proved impossible. Due to the distance of 50 km and the large angular distance between the transmitters, switching the CITY antenna to active mode did not help either.
Frequency spectrum (ST-6986 meter) for the CITY antenna pointed at the no. 1transmitter. Clearly visible higher levels for channels: 21,22, 25 and 43. For the no. 2 transmitter selected with the channel 36 marker, trace signal strength is recorded.
Accordingly, the antenna set was enlarged with a second antenna, DIPOL SMART Horizon A2230
. Directing it to the transmitter number 2 resulted in correct reception already in passive mode:
The frequency spectrum shows a significant increase in signal strength on channel 36 from the no. 2 transmitter, compared to the first antenna (CITY) aimed at the no. 1 transmitter. The Horizon antenna also receives signals from the no. 1 transmitter, located relatively close to it, but due to its orientation to the no. 2 transmitter, the power of these signals is lower than that of the CITY antenna.
Note that the relatively low signal power obtained in passive mode for channel 36 (less than 40 dBuV) may result in reception problems in inclement weather. In addition, given the need to use the Terra PA420T channel amplifier to distribute the signal to 70 receivers, it should be taken into account that the required minimum signal level at the input of the amplifier is 50 dBuV. Therefore, it is reasonable to switch the Horizon antenna into active mode by applying DC 12 V to the built-in amplifier in the antenna box.
The signal power increased by 22 dB to 58 dBuV. This is already the power that should ensure stable reception and, just as importantly, sufficient to feed it to the input of the Terra PA420T amplifier. It is worth noting that switching the antenna to active mode did not deteriorate the quality of the received signal – the MER ratio remained unchanged (27.9 dB).
The antenna set up and configured this way is ready to be connected to the channel amplifier.
It was decided to choose the PA420T Terra model because of its built-in power supply. The additional UHF input can be used in the future, e.g. to connect a modulator signal (integration of TV system with CCTV system, etc.).
The Horizon antenna uses IN 1 input, the CITY antenna uses IN 2 input.
The PA420T amplifier has the ability to power antenna preamplifiers on both input number 1 and input number 2 (designated DC OUT).
The TerrNet application was used to configure the amplifier. The capabilities of the application and how to configure Terra channel amplifiers are shown in detail in this video:
Before turning on the DC OUT voltage at the IN 1 input, it was ascertained that the signal received by the Horizon antenna on channel 36 had too low a power to excite the amplifier's AGC circuit.
To do this, a filter was selected for the IN 1 input on channel 36, and then switched to a graphical visualization of the frequency spectrum. The green bar indicating the signal strength at the input showed 50 dBuV. This is the minimum signal value that is presented in the application's graphical interface. All signals with a power lower than 50 dBuV (in this case 36 dBuV) will be presented this way. The black bar is the output level set on the amplifier (100 dBuV).
As expected, the amplifier is not working properly. The signal level for channel 36 is too low to drive the amplifier circuit correctly. This is proven (in addition to the lack of signal at the output) by the flashing red Error LED on the housing of the device.
Switching the Dipol SMART Horizon antenna to active mode requires only turning on the power at the IN 1 input of the amplifier.
Configuration of the IN 1 input of the amplifier: channel 36, preamplifier power on.
After turning on the preamplifier, the input signal power level increased to about 60 dBuV and reached the required minimum (50 dBuV). The amplifier is working properly.
The IN 2 input remained to be configured, to which the CITY antenna was connected, directed at the local transmitter that broadcasts MUXes on channels: 21, 22, 25 and 43.
Full input configuration of the PA420T Terra amplifier for two UHF antennas connected to IN1 and IN2 inputs. IN1 input – Dipol Horizon antenna operating in active mode, IN2 input – Dipol City antenna operating in passive mode.
Assuming signal attenuation of about 40 dB, when split between 70 receivers, the output level of the amplifier was set to 100 dBuV. The amplifier equalized power for all channels. The built-in AGC circuit is responsible for stabilizing the output signal in case of power fluctuations in the input signals. The parameters were also confirmed by measurement with a meter, the power of channels: 21,22,25,43 and 36 was equalized to about 100 dBuV. The quality parameters did not deteriorate.