AN307

2

Rev. 0.2

2.2. Minimum Averaged Noise Level

By using the average of several frequency bins, the algorithm selects stations away from strong adjacent channels

because certain receivers suffer from poor blocker performance. The noise is averaged over the current frequency

±1 channel to arrive at the measurement. To reduce the effects of noise floor shaping, the algorithm divides the FM

spectrum into several separate bands and finds the lowest power in each (same as algorithm 1). Figure 2

illustrates an RPS spectrum (in red) along with the averaged noise level spectrum (in black).

Figure 2. Selecting Stations Using Average Minimum Power in Five FM Frequency Bands

Certain receivers may suffer from poor performance due to blockers at either adjacent (N±1) or alternate channels

(N±2). As a further enhancement, the RPS scan algorithm can incorporate alternate channels by averaging over

five channels (N–2, N–1, N, N+1, N+2). The averaging is weighted using the coefficients (1, 2, 6, 2, 1) and then

normalized by the sum of the coefficients. The current channel (N) has the most effect on the averaged value

(coefficient value 6), followed by the adjacent channels (coefficient value 2), and finally the alternate channels

(coefficient value 1). This algorithm improves performance with receivers that are sensitive to alternate channel

interference.