Transmitter parameter

AN4126

12/28

Doc ID 023299 Rev 1

3.1.2

Carrier frequency separation

Frequency hopping systems must have hopping channel carrier frequencies separated by a

minimum of 25 kHz or the 20 dB bandwidth of the hopping channel, whichever is greater.

The measurement is performed in conducted mode connecting the SPIRIT1 application

board to a spectrum analyzer. The RBW (resolution bandwidth) of the spectrum is set to 100

kHz, the VBW (video bandwidth) is set equal to the RBW. The center frequency of the

spectrum analyzer is set to the middle of the hopping channel, the span is adjusted wide

sufficient to see the hopping channels. Since the FCC refers to the carrier frequency

separation, this parameter can be measured on either an unmodulated or modulated signal.

The measurement on the SPIRIT1 is done with an unmodulated carrier. The measured

channel separation is the minimum possible, 25 kHz, and the hop is shown in

Figure 5. If

numerous data rates and deviation settings are applied for different modes of operation, a

separate measurement must be made for each mode.

Figure 5.

Minimum carrier frequency separation measurement

3.1.3

Number of hopping channels

Frequency hopping systems operating in the 902 - 928 MHz band use at least 25 or 50

hopping frequencies. To perform this measurement, set the spectrum with the start

frequency to 902 MHz and stop frequency to 928 MHz. The RBW (resolution bandwidth) of

the spectrum is set to 100 kHz, the VBW (video bandwidth) is set equal to the RBW.

In the SPIRIT1, the full bandwidth coverage is measured with 53 jumps from 902 MHz to

928 MHz with a step of 500 kHz. So it is possible to show that more than 50 hopping

channels are covered by SPIRIT1, making it useful in applications that want to work on FCC

part 15.247 frequency hopping systems.

AM13150v1

-60

-50

-40

-30

-20

-10

0

10

20

9.151E+08

9.151E+08

9.151E+08

9.151E+08

9.151E+08

9.151E+08

Frequency [Hz]

25 kHz hopping