I need to have RF transmitter on a mcu board with 12 Volts supply to send small ammounts of periodic data to a RF reciever board connected to computer (via RS232 or USB).
The range I am looking for is 100 meters with 2 or three concrete walls betweeen them.
I saw some ICs with different frequency ranges.
There will be multiple transitters in the same area so collision should not spoil the communication.
What would be the suggested frequency range for such usage? Also what are other things to consider.
Any particular Rx/Tx pairs using I2C or SPI or USART based?
Even with 1watt radios you can find that concrete and steel walls kill your signal. I'd borrow a pair of cheap walkie talkies on 446MHz or 465MHz (whatever is allowed in your country) and try them at the location to get an idea of how well it is going to work. I'd also buy a single pair of data modules first and try them before buying lots. Running a cable to get the receiver antenna in the same space as the transmitters will make a huge difference.
UHF generally works better than VHF in buildings. That means
315/418/433MHz. You need to check what is license exempt in your country (or how much hassle and expense it would be to get a licensed frequency). 865MHz is a bit high but might be suitable. 100mW data transmitters on 418/433MHz are cheap.
At UHF you can find it work in one spot and dosn't work in another spot 30cm away. The problem is that the signal bounces around, the direct signal and a refleted signal can arrive out of phase and cancel out. That is why wifi access points usually have two antennas. Multiple receivers will be required for good performance.
Directional antennas on the fixed equipment will help. Outdoors you can sometimes find that point the antenna at the big building in the distance that the signal is bouncing off can work better then the direct path.
That's a protocol issue. If you have one way comms you can only transmitt with a low duty cycle at random intervals, not have too many transmitters on a channel and accept there is some probablity of it not getting through for a period of time.
If you have two way comms the main unit can poll each unit seperatly.
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