GPS satellites transmit several different carrier frequencies and apply different modulation codes to those carriers. The NetRS is capable of tracking several kinds of codes. On the L1 frequency (~1575 MHz) the C/A-code is always tracked. On the L2 frequency (~1255MHz), two codes may be available. On older satellites, the encrypted Y-code is usually all that is available. This signal was designed for military users and cannot be tracked directly without using militarized equipment. The NetRS normally uses a Trimble-proprietary cross-correlation method to track these Y-code signals.

Newer GPS satellites may modulate the L2 frequency with a second code designed for civilian use. This is the L2 Civil Signal, often refered to as L2C or sometimes L2CS. The NetRS is able to track L2C signals when they are available. Note that the first L2C-capable satellite was launched in late 2005, and it will take some time before a significant number of other L2C-capable signals are available. As of this writing (March 2006) only PRN 17 is transmitting L2C.

You can choose which signals your NetRS will attempt to track on the L2 channels by using the L2 Tracking Control page. There are four modes available which affect tracking on all GPS satellites.

• Off
  This mode disables tracking of any codes on the L2 Channel.
  The L2 Signal-To-Noise values in the Satellites-Tracking Information page will all show '-' to indicate that no L2 signals are being tracked.
  
  
• L2-Y-code Only
  This mode enables tracking of the L2-Y-code signals using cross-correlation. L2C tracking will not be attempted. This is the default setting when a system is reset to factory defaults.
  Signal-To-Noise values in the Satellites-Tracking Information page will all show the C/N₀ value when the L2 signal is acquired.
  
  
• L2C or L2-Y-code
  In this mode, the NetRS will attempt to track L2C signals. If an L2C signal is found on a satellite, then the L2 measurements for that satellite will be based on L2C. If the L2C code is not found, the NetRS will fall back to tracking the Y-code using cross correlation.
  Signal-To-Noise values in the Satellites-Tracking Information page will all show the C/N₀ value on L2C signals with a C prefix, like this    C38.2.   Values without the C prefix are from an L2-Y-code measurement.
  
  
• L2C and L2-Y-code
  In this mode, the NetRS will simultaneously track both L2C and L2-Y-code signals.
  Signal-To-Noise values in the Satellites-Tracking Information page will show the L2-Y-code SNR, or the L2C SNR (with a C prefix), or will show an SNR reading for both signals, as with 34.3 / C38.2.
  Note that some data logging and streaming output formats (like Binex) may not support this mode.