Calculate bandwidth for MSK signal and predefined settings in SmartRFStudio7

johanlt

Other Parts Discussed in Thread: CC2500

Hi,

I have question about the calculated bandwidth found in "Typical settings" in SmartRFStudio7 for MSK modulated signals (mod.ind.=0.5):

250KBaud/540KHz

500Kbaud/812KHz

Using Carsons rule, BW = 2(fb+0.5fb) this should be:

750KHz and 1500KHz respectively?

can anyone help clarify how the predefined bandwidth is found?

over 11 years ago

0 Eirik V over 11 years ago

TI__Guru 56590 points

Hello Johan T,

Greetings from forskningsparken.

If I am not mistaken I think the formula is:

BW=2*deviation + baseband data rate

For the 250KBaud at MSK (Deviation = 62.5 kHz) this would give:

2*(62.5e3) +250e3 = 1.5*'Data Rate) = 375 kHz.

MSK signals will have a narrower bandwidth than general FSK signals. If you apply this formula on the two other data rates given in the data sheet (2.4kHZ and 10 kHz) you will get much closer to what is measured by using carson rule. If you read the following section in the CC2500 data sheet : "4.3 RF Transmit Section" you will find a table that tells you the occupied bandwidth (99%) for the different data rates:

250 kBaud, MSK - 296 kHz

500 kBaud, MSK - 489 kHz

The typical settings is based on measurements and tuning done in the lab, so it also might have been some manual trimming involved without using calculations to get the optimal value.

Edited: Corrected formula used