The Measurement Corner
"UAL - Universal Auto Lock"
One of the most cumbersome processes for an installer is finding the correct parameter to lock onto a specific digital channel. Whether satellite or cable, the Symbol Rate is one of those parameters needed. Finding the correct one and then having to enter it into the field spectrum analyser could affect the otherwise smooth flow of our installation certification methods.
All truth be told, the actual process is not complicated, in fact, we do it every single day in our day-to-day work. However, it does matter especially in large installations where we may have a mixture of digital services in various modulations.
Whenever digital satellite services need to be measured and checked, the installer must always show up on the job with an updated version of the satellite services and parameters list, because locking onto these channels to measure their quality is only feasible if we know the correct SYMBOL RATE of the transponder to enter into the meter.
In case of cable distributions with DVB-C channels, it is fairly common that those channels are generated utilising DVB-S to QAM, or DVB-S2 to QAM transmodulators. In this case, the Symbol Rate of the output channel can be calculated using the following formula:
Where Nbits is:
As told before, these manual processes are truly frustrating when dealing with large installs with a mixture of transmodulated services. We usually tend to speed up the measurements at these sites by exploiting the automatic processes that most of the field spectrum analysers grant us these days, such as the SCAN&LOG functionality, that sweeps the entire frequency finding all the channels available and performing all the necessary checks on them. However, the automatic effect is lost when the meter stops at every channel until the installer introduces the correct symbol rate. In other cases, the meter does find the symbol rate by a process of trial and error until finding the right one.
Either case, a very slow process.
Now the H45 meter offers an intelligent solution. Televes has developed and patented a mathematical algorithm that allows the processor of the analyser to read the real symbol rate of the channel being measured, so that in almost real-time and automatically, we are locked onto the channel measuring all its characteristics.
Fig.1 shows how the H45 has read symbol rate 6104 and has locked automatically on the channel. Fig.2 shows all the possible digital measurements of the QAM channel once locked.
Fig. 3 shows that the true symbol rate in the QPSK channel selected is 22004, not the typical one of 22000 generally used. This shows the absolute precision of this measurement tool. In the same way, fig.4 shows that the true symbol rate utilised is 27498.
Once locked by reading all the parameters automatically and in miliseconds, the H45 shows us all the possible measures of these digital channels. Fig.5 shows an example of measurements of a DVB-S2 tansponder.
The digital algorithms necessary to extract the information from the channel are quite complex and their execution in a compact and light field spectrum analyser can only be achieved thanks to the latest DIGITAL PROCESSING technology available. This technology allows to extract the symbol rate of any modulation scheme (DVB-C, DVB-S, DVB-S, DVB-S2 ), even the ones used commonly in the USA (DSS y 8PSK), in less than 1 sec and without the need of trial-error processes.
Hence the name given to this jewel of funcionality... UAL (Universal Auto Lock)..