I am using a sender and a receiver for the 433MHz band, looking like these.
Is it possible to share the send and receive antenna and attach one good instead of two wire antennas?
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I have a reference design for a similar type of 433MHz transmitter / receiver modules and while I can't share the schematic due to an NDA for this particular pair of modules connecting the transmitter output directly to the receiver could exceed the absolute maximum emitter to base voltage on the input stage of the receiver. It would depend on what particular transistor your module uses and its configuration but I wouldn't consider it a safe thing to do in the absense of other information and often the transistors aren't clearly marked.
I've never actually tried doing this but looking at the receiver circuit using a low-side switch on the path to ground would prevent that and might be worth a try, although it looks like it may end up radiating some RF back into the positive supply rail so you might need some extra filtering from the positive supply rail on the receiver to ground.
Depending on your microcontroller (if using one) and its current sinking capability you could try switching the ground of the receiver using a floating / low I/O pin, although it's hard to know how well the mix of RF and digital circuitry would work together. Otherwise a fairly neat alternative might be to use something like figure 8 speaker cable with a different conductor for the transmitter and receiver.