[mcdonaldREMOVE TO ACTUALLY REACH [email protected]]

Scott Dorsey wrote:


You want goofy, look up where the 50 and 75 ohm transmission line
standards came from...


That's not goofy. The impedance of free space is (about) 75 ohms, as
is, not accidentally, the impedance of a matched dipole antenna.

The minimum loss of a coaxial transmission line with air insulation
occurs at 75 ohms (for the same reason!) while the minimum
loss for a coax line with plain polyethylene insulation is at
50 ohms approximately. Foam insulation line is intermediate.

It is a pain in the butt that TV (cable and receiving antennas) uses 75 ohm
lines while almost all other RF electronics equipment is 50 ohm.

Doug McDonald