DocID024318 Rev 1

7/20

AN4271

Transmitter parameters

2

Transmitter parameters

All the measurements reported here have been measured with the following parameters: T

C

= 25 °C, V

DD

= 3.3 V, f = 869.500 MHz.

The adjacent channel power, modulation bandwidth and unwanted emissions in the

spurious domain measurements are also reported. The measurements are performed in

accordance with EN 300 220 v1 [

2].

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 narrow band systems.

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

modulation. The ACP is measured with a spectrum analyzer conforming to the requirements

given in the EN 300 220-1 v2.4.1 (2012-01) [

2] annex C.

In this application note, the ACP measured with 12.5 kHz channel spacing is investigated.

For this measurement, the integrated bandwidth of the adjacent channel is 8.5 kHz. The

ETSI limits for the ACP is 10 μW (-20 dBm) for channel separation of 12.5 kHz.

Figure 5 illustrates the measured ACP at the 869.5 MHz center frequency. The data rate is

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

Gaussian FSK (GFSK) with a BT = 0.5.

The output power integrated around the carrier is 27 dBm in 8.5 kHz bandwidth. With this

power the ACP is -30 dBm, which is 10 dB better than the ETSI limit.

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

requirements, with margin.