Search Offset (Digital Demod)

The VSA specifies an offset, in symbols, when sync search is used. The offset determines the location of Result Length within Search Length, as shown below:

$image\syncoffset.jpg$

A positive or negative offset can be specified. If the SYNC pattern occurs before the start of Result Length, specify a negative offset. If it occurs after the start of Result Length, specify a positive offset.

The following illustration shows a SYNC pattern surrounded by several fields of data. The SYNC pattern is 14 symbols in length; each field is 10 symbols in length. The illustration shows you how different offsets can be used to view different fields.

$image\syncoffset2.jpg$

The VSA can change the offset after the signal is demodulated.

Minimum and Maximum Offset

The minimum and maximum offsets entered depend on these parameters:

Search Length
Result Length
Search Pattern

Basically, any offset can be entered such that the Result Length falls within the Search Length. Increasing any of these parameters affects the maximum positive or negative offset that can be entered as follows:

Increasing Search Length increases the maximum positive or negative offset that can be entered.
Increasing Result Length decreases the maximum negative offset that can be entered but has no effect on the maximum positive offset.
Increasing the length of the Search Pattern decreases the maximum positive offset that can be entered but has no effect on the maximum negative offset.