5.  Use the arrow keys and scroll 
wheel or number pad to enter 
the Span/Center frequency. 
To sweep from low to high frequencies, set a 
positive span. To sweep from high to low 
frequencies, set a negative span. 
 
When Marker is off, the sync signal is a square 
wave with a 50% duty cycle. When the sweep 
starts, the sync signal will be at a TTL low and will 
transition to a TTL high level at the center 
frequency. The SYNC signal frequency is equal to 
the specified sweep time. 
 
When Marker is on, the SYNC signal is at a TTL 
high level that drops to a TTL low level at the 
marker frequency.