Ross SRG-4400, User Manual

Page: 184 / 193

14–10 • GPS Option SRG-4400 User Manual (Iss. 06)
Thermal noise is -174dBm/Hz at room temperature. From this we can compute a system noise
figure of 4dB for the SRG-4400. This noise figure consists of the loss of the preselect SAW filter,
the noise figure of the LNA as well as implementation losses within the digital signal processing
unit.
Simplified GPS Flowchart
Figure 14.8 Phasing to GPS Flowchart
YES
Found
GPS
Time?
Lost for
>1 hour?
NO
NO
Power On
Clear 25Hz Lock,
Clear 29.97Hz Lock,
Clear 30Hz Lock
YES
Search for
GPS Frequency
Is the
Error
<1ppm?
YES NO
Is the
Error
<0.1ppm?
YES NO
Set TLock
Set TiLock
FrameCount
= 25Hz
Phase Lock
Point?
YES NO
FrameCount
= 30Hz
Phase Lock
Point?
YES NO
Set 30Hz Lock
FrameCount
= 29.97Hz
Phase Lock
Point?
YES NO
Set 29.97Hz Lock
Set 25Hz Lock
Search for GPS Time
Set TaLock