Date of this Version
United States Patent (19) Layland et al. 4,112,497
Apparatus for demodulation and correlation of a code modulated 10 MHz signal is comprised of a sample and hold analog-to-digital (A/D) converter synchronized by a frequency coherent 40 MHz pulse to obtain four evenly spaced samples A1,B1A2 and B2 of each cycle of the signal, and means for adding, or subtracting, each sample to, or from, one of four accumulators to form the sums:
SI, = (A1-A2) M1
Sia=; (A1-A2) M2
S2, = (B1 - B2) M1
S2= (B1-B2) M2
M1 = 10 MHz Reference . Receiver Code A0' M2 = 10 MHz. Reference . Receiver Code A90'
M2 = 10 MHz. Reference . Receiver Code A90'
The correlation functions that are used for the range measurements are then computed from the following equations:
I = S1 cos a - S2 sin a
Q = Sicos a - S2 sin a
where sin a and cos a are determined at the start of each range acquisition by forcing the receiver code for both M1 and M2 to be equal to 1 and applying these equations: