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CC1125: deviation in smartrf studio 7 typical settings

stark stark
Prodigy 40 points

Part Number: CC1125

2GFSK need h=0.4~0.7，but all deviation in smartrf studio 7 typical settings are not satisfied。

I want to know why？

  • 0
    TI__Guru**** 317180 points
    Not sure what your question is. What do you mean by "2GFSK need h=0.4~0.7"?

    If you need a different modulation index than the settings in SmartRF Studio you can just change the deviation to what you need.
  • 0 in reply to TER
    Prodigy 40 points

    sorry，my english is poor.

    the book said: the modulation index of MSK must be 0.5. the modation index of 2GFSK is not strictly limited,it is suitable from 0.4 to 0.7.

    but the modulation index in smart rf studio typical settings do not obey the rule, also can be any value.

    i can not understand this。

  • 0 in reply to stark stark
    TI__Guru**** 317180 points

    "The Book" is not very specific. Are you sure that the book refers to modulation inxed and not BT, see ?

  • 0 in reply to TER
    Prodigy 40 points
    thanks!
    the boot is not writen in english,but it is not BT.
    for example，bluetooth technology use gfsk with BT=0.5,h=0.28~0.35.
    i think there are some reason to limit the h. i want to know the rule.
    if smart rf studio allow the value of h, how does it affect the bit error rate.

    www.ukessays.com/.../bluetooth-connection-gfsk.php
  • 0 in reply to stark stark
    TI__Guru**** 317180 points
    Without knowing the book and the context the book uses I can't comment on why they have a limitation for h. A modulation index equal to 1 gives in most cases a good tradeoff and we use this for higher datarates normally. The modem can have a limitation for min/ max h due to how it's implemented but the min/ max values is far from what your book state.
  • 0 in reply to TER
    Prodigy 40 points

    I cannot find the The English version of that book.

    I find the modulation index of the bluetooth specifiation as the following figure.

    I feel a little dizzy.

    Do you have theoretical reference paper about how to set the modulation index?

    thanks!

  • 0 in reply to stark stark
    TI__Guru**** 317180 points
    Your question is about CC1125 from the heading. BLE has nothing to do with CC1125 so you can't compare with this.

    From a previous post on setting deviation:

    "Theoretically, there is an optimum separation/datarate setting if you simultaneously minimize the Rx filter bandwidth. Every halving of Rx filter bandwidth increases sensitivity with 3 dB whereas sensitivity vs separation/datarate (modulation index) decreases with about 1.5-2.5 dB per halving down to a certain limit where the loss increases very fast (I wouldn't go below a modulation index less than 0.5). Our experience is to that a modulation index of 1 is a good compromise. Note that the frequency offset between Rx and Tx needs to be taken into account when selecting the Rx filter bandwidth. "