Pulse Search Enable (Custom IQ)

Pulse Search demodulates pulsed (burst) transmissions. Selecting the Pulse Search check box turns on Pulse Search; clearing it disables Pulse Search.

Digital communication systems that use pulsed transmissions send and receive information in bursts (such as those in mobile units). In other words, carrier power is switched on and off. The carrier switches on when the transmitter transmits data and switches off when the transmitter finishes transmitting data. If Pulse Search is on, the demodulator searches within the defined Search Length to locate the first complete pulse, which can occur anywhere in the Search Length. Pulses beyond the first complete pulse are disregarded and are not demodulated. In order for the Pulse Search algorithm to detect a pulse edge, the pulse must be at least 15 dB above the noise floor. The resultant pulse is then demodulated. If Pattern Search is selected in addition to Pulse Search, the demodulator performs Pulse Search first then performs sync search on the resultant demodulated pulse as illustrated below.

$image\pulsesearch_wmf.jpg$

The Result Length, which includes both the offset and the sync word, must not violate the boundaries of the demodulated pulse.

Using Pulse Search

There are two ways to use Pulse Search:

Pulse Search with Pattern SearchOFF
Pulse Search with Pattern Search ON

Pulse Search with Pattern Search OFF

When Pulse Search is used and Pattern Search is disabled, these parameters determine how the demodulator searches for the pulse and the data that is demodulated:

Search length determines the length of time over which the demodulator searches for a complete pulse (off-on-off).

The trigger signal determines when the demodulator begins its search.

Result length determines how much information is demodulated. Only the first pulse detected in the search region is demodulated.

The demodulator automatically centers the Result Length with respect to the pulse. In other words, the demodulator positions the Result Length around the center of the pulse, as shown below.

$image\pulsedmd_wmf.jpg$

Pulse Search With Pattern Search ON

When Pulse Search is used and Constellation Sync Search is enabled, these parameters determine how the demodulator searches for the pulse and the data that is demodulated:

When Pattern Search is ON, the demodulator searches for a pulse within the Search Length. The demodulator demodulates the entire pulse to locate the synchronization pattern (also called sync pattern or sync word). If there are multiple pulses within the Search Length, the demodulator demodulates only the first pulse.

The demodulator uses the Search Pattern and the Search Offset to position the Result Length¾the Result Length is NOT centered around the center of the pulse.