Dawnco STARLOOK- D Руководство - Страница 7

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2. Digital

STARLOOK- D can easily and very accurate measure at digital transponders (MPEG-

streams).

This kind of measuring is very good to do when an installtion is done, to control and verify that

the installaion is correct performed (fingerprint of the installation).

It is less accurate when trying to find a satellite and adjusting the cross-polarisation.

Therefore, start with finding the "right" satellite with the spectrum-function. Check and adjust

the cross-polarisation with the "Max zoom in" function.

Chose a suitable transponder (put the cursor on top of a "peak") and select function 2 in the

Mainmenu (Digital).

The monitor displays, in the left upper corner, the so called, constellationsdiagramme (QPSK).

To the right of it, 4 "lock-parameters" and a time counter (that shows the "lock-time" on a bit-

stream") are shown.

The other measured data like the S/N-ratio (signal/noise ratio) och BER (bit error rate) are

displayed just under the constellationdiagram in the shape of Bar-graph´s (thermometer-scales).

A locked frequency can look like this.

Notice:

• The constellationdiagramme is like "a shower of hail". No signal will spread out the

noise over the window. The better signal the more concentrated "hailstorm".

• SNR. The signal/noise ratio should be as high as possible. A good signal should have at

least 8.0 dB S/N-ratio.

• BER. The Bit Error Rate should be as low as possible.

As the values are really small, on the other side of zero (presented as something raised to

minus something), they should be as high as possible.

A BER at 5.00 –05 is therefore better than 9.00 –04.

A BER at 4.00 –05 is therefore better than 5.00 –05.

It can be said, in general, that a signal should be at least x.xx –04 to be accepted.

DAWNco • 3340 S. Lapeer Rd • Orion, MI 48359-1320 • Ph (248) 391-9200 • Fax (248) 391-9207 • [email protected]

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