3.2 Several trials during single burst

More than one trial can be made with a scanning receiver during a burst when the dwell time of the receiver at a specific frequency position is sufficiently short in comparison with the burst duration (FIG 6). A number of n valid trials may be performed during consecutive dwell times Td of the receiver within the burst period Th. An intercept attempt is considered valid when the integration time is completely covered by the burst, ie if no frequency change or start and stop of a burst occurs during the integration time Ti of the detector. The number n depends on the timing of the burst Th and the receiver dwell time Td at a specific frequency position. The following applies for the mean number n of valid intercept attempts during the hop period T_h :

The derivation of this equation is presented in the blue BOX. During a search, each intercept attempt of the receiver is made at a different frequency position, so the probability of hitting the burst increases with each attempt beyond n = 1during a burst period. The probability of intercepting a burst with n valid
attempts within T_h is therefore defined by:

The validity of (8) has the following limitations:
a) A basic precondition is T_h / T_i > 1, ie a burst can only be detected if it is
longer than the detection time.
b) The probability defined by (8) can theoretically be P1 h > 1 provided ( T_h -T_i )/Td is long enough. However, with a long burst duration T_h , the highest intercept probability P_{1 hmax} <= 1 is reached when the search receiver is able to scan all MSc channels during one burst (burst time longer than complete scan, T_h > T_Sc ). When T_h is further increased, the probability of intercept for a single burst does not rise above P_{1 hmax} . T_h > T_Sc yields n = M_Sc /K and thus the following limits apply to (8):

The maximum achievable probability of intercept in the case of long bursts depends on the degree of overlap of the hop range with the receiver scan range.
a) General case (FIG 5a):

b) The hop range is completely covered by the scan range M_Sc <= M_FH:

c) The scan range is completely within the hop range M_FH >= M_Sc:

A comparison of (8) and (3) shows that greater probability of intercept can only be reached at sufficiently high scan speeds:

If only the basic condition T_i < T_h is met but not (13), it is possible that on average less than one valid intercept attempt can be made during a burst. In these cases the probability of intercept for a single burst is reduced according to as against.