I have designed a receiver at 440 MHz with a 10 MHz signal bandwidth. I have measured the sensitivity of the receiver in a cabled setup (coax cable between transmit and receive) and that is about -93 dBm at the moment.
If I connect an antenna at both ends in line of sight, my receiver sensitivity becomes -83 dBm (a loss of about 10 dB in over-the-air setup vs cabled). Is that expected? I can see that as soon as I connect the antenna to my receiver, the noise power increases by about 10 dB (although there is no other signal at 440 MHz at the site where I am testing). That increased noise power is contributing to the link failure at -83 dBm instead of -93.
My question: is that why the noise floor goes up by 10 dB? Is that expected?