Furuno 1834C-BB User Manual

2. RADAR OPERATION 

Radar
antenna

Radar
mast

Funnels, stacks, masts, or derricks in the path of the 
antenna block the radar beam. If the angle subtended 
at the antenna is more than a few degrees, a 
non-detecting sector or blind spot may be produced. 
Within this sector, targets can not be detected. 
 
 
 
 
 

A Search and Rescue Transponder (SART) may be triggered by any X-Band (3 cm) radar 
within a range of approximately 8 nm. Each radar pulse received causes it to transmit a 
response which is swept repetitively across the complete radar frequency band. When 
interrogated, it first sweeps rapidly (0.4 

µs) through the band before beginning a relatively 

slow sweep (7.5 

µs) through the band back to the starting frequency. This process is 

repeated for a total of twelve complete cycles. At some point in each sweep, the SART 
frequency will match that of the interrogating radar and be within the pass band of the radar 
receiver. If the SART is within range, the frequency match during each of the 12 slow 
sweeps will produce a response on the radar display, thus a line of 12 dots equally spaced 
by about 0.64 nautical miles will be shown. 
 
When the range to the SART is reduced to about 1 nm, the radar display may show also the 
12 responses generated during the fast sweeps. These additional dot responses, which 
also are equally spaced by 0.64 nm, will be interspersed with the original line of 12 dots. 
They will appear slightly weaker and smaller than the original dots. 

9500 MHz

9200 MHz

Radar antenna
beamwidth

Lines of 12 
dots are 
displayed in 
concentric 

Echo from SART

Position of
SART

Own ship
position

Own ship
position

SART mark
length

Radar receiver
bandwidth

Sweep time

7.5 

µ

s

 95 

µ

s 

Sweep start

High speed sweep signal

Low speed sweep signal

24 NM

1.5 NM

Position of
SART

Echo from
SART