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General Overview
The setup and verification procedure does not depend on a broadcast standard. This guide uses ATSC 3.0 signal for reference only. If any additional actions defined by the standard specifics are required, they are addressed in special notes.
1. Connect an RF signal source to the desired RF input.
Note: AVQ200 supplied with one RF input only. AVQ1020 and AVQ1022(1U) can be optionally upgraded to the second RF input. AVQ1022(mobile) has two RF inputs installed.
Note: If possible, please check the input power level to ensure that it is in the range listed in the technical specifications for the device
2. Set parameters
Using Control Panel -> Configuration -> Settings Menu (see Figure 1) set the following parameters:
- Desired RF input (RF1 or RF2 if installed)
- Central Frequency in kHz
- Mode of operation Tx Output (AVQ1020/AVQ1022) or Off-Air (AVQ200/AVQ1022)
- Desired signal bandwidth, if applicable
Figure 1 - Setting initial parameters
Note: The Settings Menu will display only supported and licensed options
3. Verify applied settings
Switch to the unit's main UI page (see Figure 2) and verify the following:
- RF input (RFin)
- Input power level (Pin, dBm)
- Central frequency (Freq, kHz)
- Broadcast standard (Standard)
- Spectrum plot including expected signal bandwidth
Figure 2 - System main web UI
In order to display signal analytics and calculated parameters, the unit should be able to demodulate the signal. The following reported parameters can be used for a high-level verification of the proper setup at this point:
- MER (SNR) value
- Status line message Processing: "No errors"
- In-band interference plot - a grey line plot inside the signal main lobe
Note: The spectrum plot bandwidth depends on the unit model and mode of operation. AVQ200 and AVQ1022 (2nd Gen) in Off-Air mode display the spectrum in bandwidth set on the Settings Menu page.
4. Verify signal statistics
The detailed statistics are available only if a valid signal (according to the selected standard) is detected and can be demodulated. Depending on the broadcast standard a set of reported parameters might be different.
Figure 3 below presents General and Spectral output (Channel and Emission) data sections, which are common for all broadcast standards.
Standard-specific parameters will be displayed in the corresponding sections. For example, Link Margin, List of PLPs, and MER/BER/Parity sections in Figure 4 are ATSC 3.0 signal specific and can be used for verification of all components of the ATSC 3.0 frame - Bootstrap, L1 signalling, and selected PLP.
Figure 3 - General statistics
Figure 4 - ATSC 3.0 PLP and Frame Components statistics
Recommendations for verification of Transmitter output RF signal critical quality parameters
The following recommendations are applicable for AVQ1020 - RF Layer Monitoring Received and AVQ1022 - RF Signal Analyzer in Tx Output mode.
I. Critical quality parameters and factors
1. Main "integral" parameters of the RF signal quality:
- Spectral emission (or Spectral Mask compliance); FCC requirements
- Modulation Error Rate (MER) (mainly for multi-carrier signals - for example, ATSC 3.0, an OFDM-based signal) or Signal-To-Noise Ratio (SNR) (mainly for single-carrier signals - for example, ATSC 1.0, a 8VSB-based signal)
2. Main factors affecting the signal quality:
- Non-linear distortions caused by a transmitter system amplification chain, especially, 3rd and 5th products falling in the main signal bandwidth and causing in- and out-of-band emissions.
- Linear distortions - Amplitude and Phase vs Frequency - caused by a transmitter system filtering circuitry, mainly by the transmitter output band-pass filter (BPF) used for filtering out unwanted out-of-band emission and comply with the FCC Spectral Mask requirements.
Notes:
- Though other factors such as, for example, Phase Noise of an internal to the transmitter (or exciter) reference source or reflected power between an amplifier and its antenna system also contribute to the signal quality, these parameters are usually thoroughly verified during transmitters installation and commissioning by manufacturers.
- Verification of the signal structure, BERs, used modulation and coding schemes, etc. is beyond current Recommendations.
- AVQ1020 and AVQ1022 in Tx Output mode expects approx. -20dB input signal level providing the most accurate measurements, though the units can still operate in 0..-40dBm range.
II. Essential tools for Transmitter output signal analysis
1. Spectrum, In-band Interference, and Emission Mask
Spectrum and In-band Interference plots together with the Spectral Output can be used for estimation of the non-linear distortions found in the RF signal and causing the signal quality degradation.
Figure 5 presents a Spectrum plot with the Emission mask (as defined by FCC) plotted in blue. The spectrum shoulder attenuation is reported in the upper left corner. The unit calculates exact numbers of the spectral emission according to the FCC rules, i.e., at offsets and resolution bandwidth defined by FCC. The exact numbers of the spectral emission can be found in the Emission section/Spectral Output table on the RF->Statistics page (Figure 6).
The In-band interference is plotted in grey. Using the plot, a user can see the interference level caused, for example, by the non-linearity products, even if the signal is sampled after the transmitter bandpass filter, thus, perfectly "shaping" the RF channel.
A toolbox (marked in red on Figure 5) can be used for setting markers or for accumulating Min/Max variations of the Spectrum and In-band interference plots.
Figure 5 - Spectrum plot with in-band interference and emission mask
Figure 6 - Spectral output according to FCC
2. Equalizer
AVQ1020 and AVQ1022 products provide a state-of-the-art built-in Equalizer. The Equalizer can be used for improving signal quality in case of the presence of linear distortions in the sampled signal.
The Equalizer is available on the ControlPanel -> Configuration -> Settings page. To use the equalizer, the following procedure is recommended:
- Switch the Equalizer Off for regular operations. The unit will report a "raw, not enhanced" signal MER/SNR as the signal received by a receiver.
- If the reported MER/SNR is low and there are no noticeable non-linear distortions, try switching the Equalizer On.
- The improved MER/SNR with the Equalizer On indicates that linear Amplitude or Phase distortions are present in the signal. To assist with identifying the distortion source, review and analyze Channel Amplitude and Phase Response plots, Group Delay and Channel Impulse Response plots listed in the RF group of data.
Note: It is strongly recommended to use Tx Output mode (Control Panel -> Configurations -> Settings -> Mode) when analysing the Transmitter output signal with AVQ1022 - RF Signal Analyzer.