I have two separate low cost 433 MHz transmitter (datasheet) and receiver modules (datasheet) running at 5V.
I wish to use them both in half-duplex operation, sharing a single antenna.
My questions are:
- Could I simply connect the antenna to both antenna pins? I am aware the full power transmission could then damage the receiver, but would this be a real risk at the low power I am operating them? I tried it on the breadboard and it worked fine, but I am not sure if there is a long-term risk.
- If not, which solution would be the simplest way to go? I am looking at this SPDT switch between the antenna and RX/TX. Is there a simpler solution for adequate performance?
Best Answer
The antenna will work identically for transmitting and receiving, so there is no limitation from the basic physics. The problem is purely one of overdriving a sensitive analog input, which is the receiver input. If the transmitter output is limited to the same power supply that the receiver runs on, this might not matter. It may temporarily make the receiver deaf for a short time after the transmission while its AGC recovers.
Look at the datasheet for the receiver carefully and see what the voltage limits are for the RF input pin. This is actually one of those rare cases where you may be able to use the absolute maximum limits instead of the operating limits if due care is used with all parameters. Your firmware knows when it is transmitting and can know to ignore anything from the receiver during that time and a short time afterward. During this time you only care that the receiver not be damaged.
A better all around solution would be to use a transceiver chip. These have the transmitter and receiver built into the same chip, with a single antenna connection. Whatever protection the receiver might need to not be hurt by transmitter RF levels has already been built in.