UNAOHM
EP2500 (Rev. 0)
43
9.1.4
How to Use the OFDM Card
Set the frequency as for a normal analogue channel. Even though the measurement may also be carried
out in the
MEA
surement mode, it may be useful to visually check for the presence of the digital signal
setting the instrument to Spectrum
EXP
ansion mode.
To initiate OFDM operations press
DIGITAL
(35)
then
OFDM
.
For the module to function properly, the PWR index reading (see Figure 20) must read “OK”. If
necessary, use the attenuator but employ the lowest attenuation possible that is compatible with the
“OK” reading.
Most of the locking parameters of the signal being transmitted are retrieved automatically by the
card, while CHBW (bandwidth) and SPECTR (spectrum polarity) must be set manually, as follows:
press
PRMT
, then
CHBW
.You can set the channel bandwidth using the shaft encoder, after which
press
BACK
,
While the OFDM module is operating it is possible to change the tuning frequency as in the case of the
UHF band in analogue, but keep in mind the fact that the response time of the instrument in the digital
mode is longer. You cannot store programs while the OFDM card is operating. However, the last
operating parameters are not lost once you have exited the function; in fact they are stored on the next
storing operation you will start, together with the other typical parameters such as such as frequency,
etc. by means of the key
↓↓
STORE
.
To exit the OFDM function press
BACK
, then
EXIT
.
For more details see APPENDIX B in this manual.
9.1.5
QAM Display Description
When the QAM module is operating, the screen indicates, from top to bottom, (see Figure 21):
•
The indication of the
CH BER
followed by the card status:
LOCKED
when the signal has been
locked,
UNLOCKED
when the parameters are not in the correct range of values and
NO
CARRIER
in the absence of an input signal.
•
The
ANALOGUE BAR
on the line below moves in a logarithmic scale to shows instantaneous
variations of the BER. This bar becomes longer from left to right in proportion to the better quality
of the signal as the BER decreases (improves). For a BER of 1E-4 (1 error out of 10000) or worse,
the printing character of the BER readings become smaller. This limit is only indicative, the decoder
may still be operative although at its extreme limits The BER measurement is valid only when the
signal is locked.
•
Further below, is the
number of uncorrected errors
RU
followed by the reading (in parenthesis) of
the amount of time taken to count the errors. The chronometer, like the RU error reading, is reset to
zero when the QPSK signal is not locked. The maximum RU count is 65535.
•
On the line below
MER
(Modulation Error ratio) of the digital channel is shown
in dB. This
measurement too, is valid only when the carrier is locked.
•
The
“CFO”
(Center Frequency Offset) indicates the difference between the carrier frequency set
and the effective operating value. As we said before, the decoder is capable of automatically tuning
with accuracy, within
±
0.5 MHz, to the frequency set). On the same line,
“PWR index”
and a
writing:
OK
,
HIGH
or
LOW
are shown. They indicates if the signal has too high a level, or too low
or just appropriate for the card to measure.
NOTE
:
The PWR index is only a response of the internal AGC (automatic gain control) circuit of the
tuner. It indicates whether the level of the signal available at the tuner input is suitable for digital
decoding (this depends on both the programmed attenuation of the instrument and the level of the signal
available at the input)
.
