What does a good coax grounding scheme look like?
Say I have some coax between a receiver and an antenna. That coax will have three currents in it:
the desired signal
an exactly equal an opposite current on the inside of the shield (really, also the desired signal)
noise on the outside of the shield
Now if there were a twisted pair inside the shield, I'd connect that pair to a differential amplifier, and the shield to the chassis. I'd be sure the currents in the chassis, which are all noise, can't flow through my amplifier.
But this is just ordinary coax, with only one center conductor. Although the signal is trapped inside the coax by the shield, and the noise is trapped outside by skin effect, what keeps the noise and signal separate once this coax terminates at the receiver? In other words, how do I provide a reference for my receiving circuitry that isn't affected by the noise currents (3)? Or, is that not possible?
Say I have some coax between a receiver and an antenna. That coax will have three currents in it:
the desired signal
an exactly equal an opposite current on the inside of the shield (really, also the desired signal)
noise on the outside of the shield
Now if there were a twisted pair inside the shield, I'd connect that pair to a differential amplifier, and the shield to the chassis. I'd be sure the currents in the chassis, which are all noise, can't flow through my amplifier.
But this is just ordinary coax, with only one center conductor. Although the signal is trapped inside the coax by the shield, and the noise is trapped outside by skin effect, what keeps the noise and signal separate once this coax terminates at the receiver? In other words, how do I provide a reference for my receiving circuitry that isn't affected by the noise currents (3)? Or, is that not possible?
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