Why are 75 Ohm and 50 Ohm BNC connectors intermatable while 75 Ohm and 50 Ohm N series are not, causing destructive damage to the 75 Ohm N connector?
The BNC connector as originally designed had dielectric material (other than air) in its interface area. Based on the impedance equation for coaxial transmission lines, the 50 Ohm BNC was 50 Ohm in its interface area (no surprise there). But several years ago, someone stumbled upon the idea of removing the dielectric material in the interface area (effectively lowering the dielectric constant) which caused the impedance in the interface area to rise up to 75 Ohm without changing the center pin diameter. However, in a 75 Ohm N series connector, the dielectric material was air already, so the only way to raise the impedance was to change the internal dimensions of the connector. Changing the outer contact would drastically change the whole geometry of the connector so instead the center contact diameter was shrunk to give 75 Ohm in the interface area. This is for both the male and female halves so the female socket will only accommodate a smaller diameter contact. Inserting a 50 Ohm cent
