MER by carrier

April 1, 2011.

MER by Carrier measurement for COFDM: Discover invisible signals

MER measurement of a COFDM multiplex has been considered until now as the average of the individual MER measurements for each of the carriers (about 8000 in a 8k system for instance) in the tuned channel. Sometimes reception quality is degraded by interfering signals that can not be detected unless we have very special analysis tools.

Field strength meter with MER by carrier function
“MER by carrier” function.
Measurement of MER for each one of the carriers.

The MER by Carrier function uses a new extremely advanced algorithm that in a matter of seconds analyses the MER for each of the carriers forming the selected channel and displays it continuously in a graphic form.

The MER by Carrier function is a measurement exclusive to the TV EXPLORER HD+ that will turn out to be very useful during the transition to digital TV where we often find cases that are difficult to troubleshoot in which signals of different types and sources interfere among them.

Field strength meter with MER by carrier function
We can confirm that this is the source of the problem just by comparing the graphic with the spectrum analyser display of an analogue channel.

An example where we use channel MER to analyse an 8K COFDM multiplex is shown on the left. We notice that there are 3 areas in the graphic where MER is degraded which tell us that an analogue channel may be present underneath.

If we compare this graphic with the spectrum analyser display of an analogue channel we realise that in effect the video, audio and colour carriers affect more intensively the MER of those digital multiplex carriers located at the same frequencies.

Fortunately the COFDM channel in this case is strong enough to be affected by this interference.

It is interesting to point out that this interference could not be detected in any other way for it can't be seen on the spectrum analyser and it is not strong enough to degrade the average MER, CBER or VBER readings substantially.