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The ADSL Graph presents a graphic display of the
number of bits transmitted in each ADSL Discrete
Multi Tone (DMT) frequency bin. ADSL modems
require wide bandwidth to operate since they
essentially use 256 separate simultaneous modems,
each requiring about 4kHz of bandwidth called a
bin. Each of these mini-modems transmits complex
symbols (‘baud’) at 4000 symbols per second. Each
symbol represents from 0 to 15 encoded bits of
information. The number of encoded bits in each
symbol depends on the SNR of the modem bin.
A significant decrease in the number of bits per
bin can result from ADSL signal attenuation or
increased noise.
Examining the bits per bin can indicate the presence
of interfering signals in certain frequency bands of
the ADSL spectrum. To identify the bin number, bin
center frequency, and bits per bin, use the [LEFT]
and [RIGHT] arrow keys to position the cursor
on the graph. The upper left box displays the bin
number (1 – 256) at the cursor position. The upper
right box displays the number of encoded bits (0
– 15) transmitted in the selected bin. The lower box
displays the bin center frequency in kilohertz.
ADSL Results Save
You can save all of the results of an ADSL Modem
test for later upload to a computer (see ‘ADSL
Results’). After an ADSL test has completed, press
the [Save] key (camera icon) to save the results.
The 965DSP will display the Save Results screen as
follows: