看起来专家都比较忙，或者是我的问题太简单。

在这问问题的多数是软件工程师，有几个能真正搞明白呢，搞明白的也去搬砖去了。

问太多，给你个回答就是看参考smart studio有意思吗？

难道真的国外的月亮圆点。唉。

The transmitted signal will have a certain signal bandwidth (BWsignal), which depends on the data rate and modulation format. This bandwidth can be approximated by Carson's rule:

BWsignal = 2*fm + 2*fdev (= data rate + frequency separation)

where

- fm is the highest modulating frequency. 2*fm = data rate

- fdev is the frequency deviation. 2*fdev = frequency separation

 BWsignal for 4.8 kbps and +/-25.4 kHz deviation is then approximated as 55.2 kHz

BWsignal for 10 kbps and +/-19 kHz deviation is then approximated as48 kHz

On the receiver side there is a channel filter, which is centered on the down-converted received RF frequency, i.e. the intermediate frequency (IF). The channel filter has a programmable bandwidth BWchannel. The signal bandwidth has to be less than the receiver channel filter bandwidth, but we also have to take the frequency error of the transmitter and receiver into account.

 If there is an error in the transmitter carrier frequency and the receiver LO frequency, there will also be an error in the IF frequency. For simplicity assume the frequency error in the transmitter and receiver is equal (same type of crystal). If the receiver has an error of –X ppm and the transmitter has an error of +X ppm the IF frequency will have an error of +2*X ppm (CC11xx uses low side LO injection). Conversely, if the receiver has an error of +X ppm and the transmitter an error of -X ppm the IF frequency will have an error of -2*X ppm.

BWchannel has to be larger than the maximum signal bandwidth BWsignal plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal errors on Tx and RX side to be of opposite signs

BWchannel > BWsignal + 4* XTALppm* fRF

where

- XTALppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading, and ageing

- fRF is the RF operating frequency.

BWsignal is more or less equal for the 4.8 kbps and 10 kbps cases above and can have the same frequency error. The deviation is set to get the same signal bandwidth and thus the same crystal accuracy requirements for the two data rates. 

The crystal accuracy, assumiing operation at 868 MHz, will be roughly 15 ppm for the 2 cases above: 4.8 + 2*25.4 + 15*868 = 108 kHz.

Finally: For a fixed RX filter BW, sensitivity vs separation/datarate decreases with about 1.5-2.5 dB per halving down to a certain limit where the loss increases very fast. Thus, you can trade sensitivity for crystal accuracy. (crystal cost)  

http://e2e.ti.com/support/wireless_connectivity/f/155/t/180039.aspx

砖家都比较忙，我的问题太简单。

The transmitted signal will have a certain signal bandwidth (BWsignal), which depends on the data rate and modulation format. This bandwidth can be approximated by Carson's rule:

BWsignal = 2*fm + 2*fdev (= data rate + frequency separation)

where

- fm is the highest modulating frequency. 2*fm = data rate

- fdev is the frequency deviation. 2*fdev = frequency separation

 BWsignal for 4.8 kbps and +/-25.4 kHz deviation is then approximated as 55.2 kHz

BWsignal for 10 kbps and +/-19 kHz deviation is then approximated as48 kHz

On the receiver side there is a channel filter, which is centered on the down-converted received RF frequency, i.e. the intermediate frequency (IF). The channel filter has a programmable bandwidth BWchannel. The signal bandwidth has to be less than the receiver channel filter bandwidth, but we also have to take the frequency error of the transmitter and receiver into account.

 If there is an error in the transmitter carrier frequency and the receiver LO frequency, there will also be an error in the IF frequency. For simplicity assume the frequency error in the transmitter and receiver is equal (same type of crystal). If the receiver has an error of –X ppm and the transmitter has an error of +X ppm the IF frequency will have an error of +2*X ppm (CC11xx uses low side LO injection). Conversely, if the receiver has an error of +X ppm and the transmitter an error of -X ppm the IF frequency will have an error of -2*X ppm.

BWchannel has to be larger than the maximum signal bandwidth BWsignal plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal errors on Tx and RX side to be of opposite signs

BWchannel > BWsignal + 4* XTALppm* fRF

where

- XTALppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading, and ageing

- fRF is the RF operating frequency.

BWsignal is more or less equal for the 4.8 kbps and 10 kbps cases above and can have the same frequency error. The deviation is set to get the same signal bandwidth and thus the same crystal accuracy requirements for the two data rates. 

The crystal accuracy, assumiing operation at 868 MHz, will be roughly 15 ppm for the 2 cases above: 4.8 + 2*25.4 + 15*868 = 108 kHz.

Finally: For a fixed RX filter BW, sensitivity vs separation/datarate decreases with about 1.5-2.5 dB per halving down to a certain limit where the loss increases very fast. Thus, you can trade sensitivity for crystal accuracy. (crystal cost)  

http://e2e.ti.com/support/wireless_connectivity/f/155/t/180039.aspx

mark!

这是老外回答的么，这么耐心。。

这里支持的都是TI中国的技术团队成员。

Nutcracker  感谢你的回复，你是对的，这些是通用的RF问题。

4. 为最好的距离表现和抗干扰表现，原则上是越小越好。为省电，是越大越好

这条指的是Channel spacing还是Rx Bw filter？

感谢！

modulation BW 在测试EN300220里面的指标！测试没有过！我该怎么调整啊！着急啊！

hi Nutcracker ：

看了你的回复，我有几点疑问：

1.你的回复是说：Rx BW 一方面需要 > 2 * Deviation + 4 * Freq. Error，但Carson's rule:BWsignal = 2*fm + 2*fdev (= data rate + frequency separation)。到底以哪个为准？？

2.根据这个公式，再结合BWchannel > BWsignal + 4· XTALppm· fRF 。再来回头看Smart RF studio中CC1310的设置，我发现RX BW和这些公式对不上啊。

比如：868M，50Kbps Symbol rate，25K deviation，晶振10ppm。那么根据Carson's rule，BWsignal = 50K + 2*25K = 100K了，而CC1310 在50Kbps下的RX BW设置为了98K < 100K，这又是为什么呢？？ 200Kbps也是同样的情况

如果根据你的公式，得出BWsignal  = 50K，加上4· XTALppm· fRF，还算比较接近98K。

可是再看300Kbps，400Kbps的RX BW值，根据你的公式，得出BWchannel 大概在250K-300K左右，但实际CC1310在这两个速率下的RX BW设置为了622K，为什么要大这么多？？

以上，还麻烦帮忙解答一下，谢谢！