The BER measurement is provided in scientific notation (i.e. 2.0 E-3 means 2.0x10
-3
, that is to say two incorrect bits of every 1,000) and
through an analogue bar (as its length is smaller the signal quality will be better). The analogue representation is done on a logarithmic scale
(not linear).
With the aim to have a reference about the signal quality, it is considered that a system has a good quality when it decodes less than one
non-correctable error for every transmission hour. This border is known as QEF (Quasi-Error-Free) and it corresponds approximately to a
BER after Viterbi of 2.0E-4 BER (2.0x10
-4
). This value is marked on the measurement bar of the BER after Viterbi and therefore, BER for
acceptable signals must be at the left side of this mark.
Next it is shown the tuning frequency and the frequency deviation in MHz between the tuned frequency and the one which optimizes the
BER (i.e. Freq: 1777.0 +1.2 MHz).
Next it is shown the number of non corrigible packets received W.P. -wrong packets- (up to a maximum of 126) in the time detailed on its
right. A packet is considered wrong when a bit is received incorrectly. To reset this measurement just modify the measurement conditions: for
example change the tuning frequency.
Finally it is shown a status line with information about the detected signal. The possible messages that can appear and its meaning are
shown in the following list. The messages are exposed from less to more fulfilment of the MPEG-2 standard:
No signal received
Any signal has been detected.
Signal received
A signal is detected but it can not be decoded.
Carrier recovered
A digital carrier has been detected but it can not be decoded.
Viterbi synchronized
A digital carrier has been detected and the Viterbi algorithm is synchronized, but too many frames arrive with non correctable errors. It is
not possible to quantify the BER.
MPEG-2
Correct detection of a MPEG-2 signal.
In case of detecting a DVB signal, message MPEG-2 DVB-S will appear and the DVB Channel Identifier function will be automatically
activated. See section 5.4.1 DVB Channel Identifier.
IMPORTANT REMARK
DVB-S channels tuning may require an adjusting process. It is recommended to follow next procedure:
1.- From the spectrum analyser mode, tune the channel at its central frequency.
2.- Switch to TV mode, BER measuring mode.
3.- If in the lower line of the screen does not appear MPEG-2 message (and consequently BER is unacceptable), by pressing keys
[6] deviate the tuning frequency until MPEG-2 message appears. Finally tune again channel to minimize the frequency
deviation which optimizes the BER and therefore minimize the BER.
If it is not possible to detect any MPEG-2 channel, make sure that digital signal parameters are correctly defined and if signal level is too
low, check that the 30 dB attenuator is not activated (Attenuator 0 dB).
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TV & SAT Level Meter MTD 120
User Manual
