This has been a question I've been thinking about for a number of years. All BNC components in the transmission of RF in professional audio (connectors, antennae etc) are 50 ohm - so how much does it matter if we occassionally use 75ohm cable to connect them all together?

I eventually put the question to Henry Cohen, wireless guru at Production Radio Rentals in New York. He replied as follows:

"The reasons the use of 75 ohm coax is not a problem are:

1. The front end of wireless mic receivers and antenna multicouplers (antenna distribution) are not truly 50 ohms. They're somewhere between 50 and 75 ohms. No RF engineer at any of the manufacturers will tell you their device is exactly 50 ohms over the entire bandsplit.
2. Antennas are not truly 50 ohms. Remember that antennas are transducers and as such have a variable impedance based on frequency. The relatively wide band antennas used in production wireless can vary anywhere from less than 40 ohms to over 100 ohms depending on frequency and near field (less than 5-6 wavelengths) obstructions.
3. Your 50 ohm coax is likely no longer 50 ohms given the wear and tear from flexing of the dielectric and connectors.
4. If one refers to the Smith Chart, a [perfect] 50/75 ohm mismatch results in less than .75dB loss, while the real world presents far greater losses simply be having the talent move around"