[RFI] [] Camera NRV RFI

[Jim Brown]

On 5/4/2020 7:28 PM, Lloyd - N9LB wrote:
> Phantom Power ( Power Over Ethernet "POE" )

These are two VERY different things. Phantom Power is a system devised 
more than 40 years ago for professional capacitor microphones (often 
called "condenser") to power electronics within the mic. Pro mics run on 
shielded twisted pair -- dynamic mics require no power. V- is applied to 
the shield, V+ is applied through equal value resistors to both sides of 
the pair that carries audio. The audio signal is only on the pair, 
signal circuits don't see the DC (originally 48V, now 9-48V), but power 
is taken between both sides of the pair and the shield.

This system concept was borrowed from the telephone system. I think it 
was called "simplex power," and may be nearly a century old.

73, Jim K9YC