FXTH871511 short range issue

snow_p — Tue, 03 Feb 2026 21:44:17 GMT

Hi,

I used 8715 board made by myself to test the launch distance is only about 3 meters, I would like to ask whether the setting of 8715 frequency deviation is correct?

The center frequency is set to 433.920Mhz, and the frequency offset is set to 20khz. Is the register of 8715 set correctly as follows?

/*********************************************************************************************
*Frequency:433.920Mhz
*Deviation:20khz
*********************************************************************************************/
//min 433.900Mhz
PLLCR0=0xb0;
PLLCR1=0x40;

//max 433.940Mhz
PLLCR2= 0xb0;

PLLCR3=0xa6

I look forward to your reply. Thank you very much.

snow

Re: FXTH871511 short range issue

JozefKozon — Fri, 24 Jun 2022 11:15:31 GMT

Hi Snow,

I have calculate the fDATA0 and fDATA1 according to the formulas in the Table 82. and Table 83. from your values you provided. Please see the results below.

PLLCR0=0xb0;
PLLCR1=0x40

0xB040=0b1011 0000 0100 0000=>AFREQ=0b1011 0000 0100 0=5640

fDATA0=fXTAL*((12+4*CF)+AFREQ/8192)

fDATA0=26 000 000*((12+4*1)+5640/8192)

fDATA0=433,9 MHz.

PLLCR2=0xb0;
PLLCR3=0xa6

0xB0A6=0b1011 0000 1010 0110=>BFREQ=0b1011 0000 1010 0=5652

fDATA1=fXTAL*((12+4*CF)+BFREQ/8192)

fDATA1=26 000 000*((12+4*1)+5652/8192)

fDATA1=433,94 MHz.

So your calculations are correct.

With Best Regards,

Jozef

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FXTH871511 short range issue

Re: FXTH871511 short range issue