AN4126

Transmitter parameter

Doc ID 023299 Rev 1

19/28

Figure 13.

Peak output power measurement

3.2.3

Power spectral density

The power spectral density conducted from the intentional radiator to the antenna must not

be greater than 8 dBm in any 3 kHz band during any time interval of continuous

transmission. The method to measure the power spectral density is similar to that used for

the conducted output power. The spectrum analyzer must be centered on the emission peak

within the signal passband. Set the RBW (resolution bandwidth) to 3 kHz and the VBW

(video bandwidth) greater than the RBW. Set the span to obtain a measured spectral line

spacing greater than 3 kHz: in this case no correction factor is required. If it is not possible to

set a measured spectral line spacing greater than 3 kHz, measure directly the noise power

density normalized to 1 Hz, then add 35 dB for correction to 3 kHz. The peak measured

signal level should not exceed +8 dBm.

To perform this measurement, the SPIRIT1 is programmed with a 2-FSK modulation with

500 kbps data rate and 250 kHz frequency deviation. The measurement result is shown in

Figure 14. The SPIRIT1 meets the power spectral density requirement with large margin.

AM13157v1

-10

-5

0

5

10

15

20

9.140E+08

9.145E+08

9.150E+08

9.155E+08

9.160E+08

Frequency [Hz]

2-FSK, 500 kbps, 250 kHz