I have a receiver device that operates on 433 MHz and uses the following hardware configuration: a PCB with an antenna connector, a short antenna extension, and the antenna itself.
Now, I need to somehow detect whether the antenna is receiving a signal at the moment or not. I don't need to understand the signal; I just need to check for the presence of a signal. This will act as a failsafe for my system, allowing me to double-check whether the signal is present. Actually, for me, it's important to know when the signal is not present.
I was thinking, maybe it's possible to sense the signal with a capacitive touch or induction sensor through the isolation of the antenna extension wire?
Reality check, here. Any antenna is always receiving a universe of signals, all the time. Your receiving system must select a small portion of those "signals" and do something with them. So, you really do need to identify if the RF being received is something you want or can be disregarded.
And a second receiver. But then you may need a third to ensure the second receiver does not miss something. Where is all this going and why do you not trust only one receiver?
My receiver control relay. If the relay fails, I want to be able to detect it. For example, if the relay is closed but no signal is coming from the transmitter, I will know that something is wrong, and I need to shut down the system. It is such that I cannot modify the receiver. I can change the cable, but I cannot modify the PCB. I was thinking that maybe there is a way to detect the signal, similar to how an RPM meter uses an inductive sensor to pick up a signal from the spark plug cable.
The common 433MHz receivers use auto gain. When there is no signal, they will increase the gain until the noise is fully amplified and send to the output pin.
The receiver software can recognize valid data between the noise.
Your solution is not fail safe, and that was the goal to begin with.
I suggest to use two-way communication with a RF module.
Can you give a broader view of your project. What the relay is for and who is the transmitter of the 433MHz signal.
It makes a big difference if the transmitter is a bought remote control or a Arduino board. Your goal is also not to check the relay. The relay turns something on and off, you want to know if that is on or off.
Perhaps you bought a relay of 10A on Ebay/Amazon/Aliexpress and wonder why the contacts melt together at 0.5A. We can tell you why.
That might work but it reduces your signal by 50%. The best way is cheat and look what they do with communications devices, they send an acknowledge to tell the transmitter they got the message. You can have your device do that each time it is activated and give position or whatever.
