Transmitter parameter

AN4110

6/18

Doc ID 023182 Rev 1

2

Transmitter parameter

All the measurements here reported are performed with the following parameters: Tc =

25 °C, Vdd = 3.0 V, f = 868.300 MHz.

The modulation bandwidth and adjacent channel power measurements are here reported.

The measurements are realized according to EN 300 220 v1 [2] sections 7.6 and 7.7.

2.1

Adjacent channel power

The adjacent channel power (ACP) is defined as the amount of the modulated RF signal

power which falls within a given adjacent channel. This power is the sum of the mean power

produced by the modulation, hum and noise of the transmitter. This measurement is

applicable only to narrowband systems.

This test measures the power transmitted in the adjacent channel during continuous

modulation. The ACP is measured with a spectrum analyzer that conforms to the

requirements given in the EN 300 220-1 v2.3.1 (2010-02) [2] annex C.

In this application note the ACP measured with 25 kHz channel spacing is investigated. For

this measurement the integrated bandwidth of the adjacent channel is 16 kHz and the ETSI

limit for the ACP is 200 nW (-37 dBm).

Figure 4 illustrates the measured ACP at the 868.3 MHz center frequency. The data rate is

set to 9.6 kbps, the frequency deviation is set to 2.4 kHz, and the modulation is set to

gaussian FSK (GFSK) with a BT = 1.

The output power integrated around the carrier is 11 dBm in a 16 kHz bandwidth and with

average detection. With this power the ACP is -39 dBm, that is 2 dB better than the ETSI

limit.

In Figure 4 the alternate channel power (ALT) is also reported. With this power the ALT is -

46 dBm. Regarding the ALT, no specification is defined in the ETSI standard.

The SPIRIT1 is fully compliant with the ETSI transmitter adjacent channel power

requirements with margin.