AN307 Datasheet, PDF (5/14 Pages) Silicon Laboratories – RECEIVE POWER SCAN PRIMER

AN307
4. Measuring RPS Algorithm Performance
4.1. Procedure
In order to characterize the performance of the RPS algorithm at selecting good candidate stations, testing should
be performed in several vehicles at different locations and with the transmitter at different locations inside the car.
This testing uses a qualitative scale measurement of Good, Acceptable, and Poor to characterize the FM receiver
performance. After the algorithm selects a candidate station, the car receiver is tuned to the station, the Si4712 is
set to transmit on the station at 115 dBuV power and the subjective audio performance is recorded. In order to
quantify the margin that the transmitter has on this particular station, the transmit power is reduced in 10 dB steps
until the audio can no longer be received. This margin is defined as the amount of power reduction from 115 dBuV
power that can be achieved while still maintaining a "Good" measurement.
4.2. Strong Signal Environment
Figure 3 shows three RPS spectra measured with a Si4712 EVB with a 10 cm board stub antenna at a location
with a direct line-of-sight view of several FM broadcast towers. This situation is representative of the strongest
signal environment likely to be encountered. Using the minimum average RNL method with the filter size set to five
channels to select candidate stations, four out of five showed good performance with the Si4712 positioned on the
dashboard. Repeating the procedure with the Si4712 on the passenger seat yielded three out of five good
candidate stations.
70
60
50
40
30
20
10
0
8750
Strong Signal Environm ent
Dashboard (Scan 1)
Good (Scan 1)
Acceptable (Scan 1)
Poor (Scan 1)
Passenger Seat (Scan 2)
Good (Scan 2)
Acceptable (Scan 2)
Poor (Scan 2)
Search Band Boundary
9250
9750
10250
10750
Figure 3. Si4712 RPS Station Scan Results in a Strong Signal Environment
Rev. 0.2
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