want guidance for choose best UART or USART RF module for Arduino

hello every body , I want to create a Star or Mesh network with arduino like image below :
the distance node between master is about 2 km.
I want to create full duplex communication , send sensor information from nodes to master node , that master node reply to each one.
witch kind of RF module is best for my solution ?
my RF module must be UART or USART , Cause of I cant use SPI Protocol , because I use SD card that use SPI Protocol.

2km? (your dreaming)

LoRa perhaps?

I think you have asked this question before. OR Maybe some one different but from your country. Is this for "farming"?

Look at xbee zigbee. Most people use the 2.4ghz frequency. It will not work when it rains. The 900mhz frequency does not have this problem. Both will work "line of sight". If you can see the other radio. At 2.4ghz it takes only one tree to kill the signal, while at 900mhz you might get through some trees. At these high frequencies the RF is much like light. It can not go through a mountain.

Use the high power version of xbee or zigbee. I can get 2km. A mesh network is good to reach long distance. Remember a good antenna is very important. Or keep and radio as high as possible.

Cicero said:

LoRa perhaps?

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This is a really good technology, but I had to bin it.... This device is designed for IOT and transmits large chunks of data... Not much use in battery applications.... I have been using ZULU and I get pretty good results... No where near the distance of LORA... Perhaps 1.5Km line of sight if I'm lucky..

How much do you want to spend?

Little Ghostman said:

How much do you want to spend?

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its better in low cost , but the importance is my issue solved .
thank you .

Can you give me a rough idea of what the budget is? I have a couple of units in mind but they are not that cheap. You might also be able to run them off rechargeable with small solar. I know these unit do 5KM easy, but there might be other options. What is the application?