in the C/A signal. A receiver capable of performing this measurement is referred to as a dual frequency receiver. Its technical characteristics are: L2C contains two distinct PRN sequences: CM (for Civilian Moderate length code) is 10,230 bits in length, repeating every 20 milliseconds. CL (for Civilian Long length code) is 767,250 bits, repeating every 1,500 milliseconds (i.e., every 1.5 second). Each signal is transmitted at 511,500 bits per second (bit/s); however, they are multiplexed to form a 1,023,000 bit/s signal. CM is modulated with a 25 bit/s navigation message with forward error correction, whereas CL contains no additional modulated data. The long, non-data CL sequence provides for approximately 24 dB greater correlation protection (~250 times stronger) than L1 C/A. L2C signal characteristics provide 2.7 dB greater data recovery and 0.7 dB greater carrier tracking than L1 C/A. The L2C signals' transmission power is 2.3 dB weaker than the L1 C/A signal. In a single frequency application, L2C has 65% more ionospheric error than L1. It is defined in IS-GPS-200. Military (M-code) A major component of the modernization process, a new military signal called M-code was designed to further improve the anti-jamming and secure access of the military GPS signals. The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P(Y) code. The new signal is shaped to place most of its energy at the edges (away from the existing P(Y) and C/A carriers). Unlike the P(Y) code, the M-code is designed to be autonomous, meaning that users can calculate their positions using only the M-code signal. P(Y) code receivers must typically first lock onto the C/A code and then transfer to lock onto the P(Y)-code. In a major departure from previous GPS designs, the M-code is intended to be broadcast from a high-gain directional antenna, in addition to a wide angle (full Earth) antenna. The directional antenna's signal, termed a spot beam, is intended to be aimed at a specific region (i.e., several hundred kilometers in diameter) and increase the local signal strength by 20 dB (10× voltage field strength, 100× power). A side effect of having two antennas is that, for receivers inside the spot beam, the GPS satellite will appear as two GPS signals occupying the same position. While the full-Earth M-code signal is available on the Block IIR-M satellites, the spot beam antennas will not be