PASS / FAIL: It may turn against you
The PASS/FAIL function is widely used in measuring instruments. Specifically talking about field strength meters it may become a great ally to check signals quickly, which turns into a double-edged sword in the hands of users if they do not know what they are doing..
In the world of signal broadcasting, one cannot presume a signal is properly received just because it reaches acceptable levels of power, MER, etc. It is necessary to take into account certain variables that cannot be diagnosed by a simple PASS / FAIL function. We will see more details further on.
PROMAX field strength meters have all the tools that truly help to resolve whether a signal meets the quality requirements or not
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Checking the pressure of three tires is enough to estimate the pressure of the fourth?
Is it reliable a mechanic who by checking the pressure of three tires estimates the pressure of the fourth?
Some field strength meters take a certain number of channels and measure their quality levels. Depending on preconfigured levels, they determine whether the entire band PASS or FAIL.
This doesn’t make any sense. The reception quality of all channels should not be estimated from the measurement of a few.
PASS/FAIL function is not enough… Why?
Mobile phone towers can turn into unacceptable a signal that under certain conditions had given the result “pass” because the installer had not taken into account the changing interferences of LTE.
When talking about field strength meters, even though when a signal status is PASS the signal is doomed to fail in a short time if measurements are not understood. Measurements must be understood, that is to say, not to succumb into the easy work temptation by focusing on the PASS/FAIL test result.
- Although the MER of a signal passes because it is within the quality threshold, it is necessary to know its measurement and the QEF limit to assess if they are too close.
- Although the Power of a signal passes it is necessary to know how to assess whether it is near the maximum limit or not, so that any unbalance of the amplifiers may cause saturation.
- Although all indicators of a signal pass, it is necessary to know how to understand the spectrum to foresee the presence of sporadic interferences, amplifier distortions such as shoulders (what are the shoulders?) or the existence of adjacent mobile phone channels.
- Even a terrestrial television signal passes, it is necessary to know and use the tools of dynamic echoes analysis to minimize the effects of the signal reflections on buildings and terrain elements.
In addition to all that we have pointed out, focusing on the result of the PASS/FAIL function based on predefined thresholds involves another hidden risk: The fact that the quality thresholds are country-dependent and even region-dependent on the same country. For example in the specific case of France:
- A national DTT channel, modulated in 64QAM, must have a MER of at least 20 dB.
- A local DTT channel, modulated in 16QAM, must have a MER of at least 10 dB.
So, PASS/FAIL function is to be used?
The pass/fail function is a great ally for those field strength meters installed at a fixed location or of rack-format construction because the user defined quality thresholds and the working environment will remain fixed – as the instrument will. That is to say, in those equipment intended for signal monitoring.MONITORING SYSTEMS
What about fieldwork? Also it is. But only in the hands of professionals who know what they are doing with a work experience that allows them to use all the tools of the field strength meter so the human, and not the instrument, who evaluates the quality of the signal relying on all the tools offered by the analyzer, not just sticking to the PASS/FAIL function verdict.PROMAX FIELD STRENGTH METERS
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PROMAX is a leading manufacturer of test and measurement systems, broadcast and TV signal distribution equipment. Our product lines include measuring instruments for cable TV, satellite TV, broadcast, wireless and fibre optics networks, FTTH and GPON analyzers. DVB-T modulators, IP streamers or IP converters (ASI, DVB-T) are among the company’s latest developments.