So This is what I understand now. When you configure the radio, parameters are set in steps. I want to target a MI of 5 but the parameters my not let me get a perfect 5, I try to stay as close to a MI of 5 as possible (based on commercial FM settings
in North
America, the maximum frequency deviation, f∆ , is 75 kHz for commercial FM broadcasting. If the maximum message frequency is equal to 15 kHz for audio, then 51575 == kHzkHzβ
To set up a 300 kbsp connection,
From rule 1, I can find my ideal target Fdev with Fdev = MI * BR/2 = 5 * 300/2 = 750
Use rule 3 to get RxBw: RxBw >= Fdev + BR/2 = 750 + 300/2 = 900 or more
Verify that it within limits with rule 2: BR < 2*RxBw == 300 < 2*900 == 300 < 1800 == TRUE
Confirm I'm within hard limits for RxBw with rule 5: Fdev + BR/2 < 500kHz == 900 < 500 == FALSE
Since I want to use 300kbps, the only variable left to change is the MI, I need to lower it no lower that 0.5 and satisfy rule 5. To satisfy rule 5 RxBw can not be higher that 500 - 150 = 350
Get new Fdev from rule 3: RxBw >= Fdev + BR/2 == Fdev <= RxBw - BR/2 == 350 - 300/2 = 200
Verify Rule 1 with rule 1 if MI is within limits: 2 * Fdev/BR = 2 * 200 / 300 = 1
So to set up a 300 kbps connection
BR=300
Fdev=200
RxBw=350
The only parameter left to figure out is RxBwAfc. I've read a little about AFC and seems that the RFM69 AFC is pretty fast so it wont really slow down the connection and according to NXP document there is a lot of advantages to using AFC.
On the other hand I haven't seen a register for RxBwAfc. Section 3.5.15 of the sx1231 talks about turning it on and 3.5.16 using Optimized Setup for Low Modulation Index Systems by setting the appropriate bits. But I'll have to read on to figure out the details.
Sid
[edit] From the "Definition of RxBw with RFM69"discusion I figured that @ 915 Mhz the LOoffset is a factor 20ppm = 18.3 Khz. What does ppm stand for here. Can't be parts per million... lol
RegAfcBw
(0x1A)
7-5 DccFreqAfc rw 100 DccFreq parameter used during the AFC => RxBwAfc value goes here ?
4-3 RxBwMantAfc rw 01 RxBwMant parameter used during the AFC
2-0 RxBwExpAfc rw 011 * RxBwExp parameter used during the AFC