Re: Dead FM Broadcasting Technologies

["Roger Kirk" <rogerkirk@ttlc.net>]

> Can one of you readers who are please explain what is meant by
> ``pre-emphasis'' and why it's measured in units of time?  (For extra
> credit, can you explain why said units of time are invariably
> represented with the wrong symbol?)

An explanation gleaned from the Internet:

Pre-emphasis and De-emphasis:
Thermal noise would be more severe at high frequencies in the baseband
To counteract this, high frequencies are de-emphasized at the receiver
To maintain flat frequency response, higher baseband frequencies are
pre-emphasized at the transmitter

Pre-emphasis and De-emphasis Circuits:
Transmitter: first-order high-pass filter
Receiver: first-order low-pass filter
Both must have same cutoff frequency
For FM broadcasting a frequency of 2120 Hz is used
This corresponds to an RC time constant of 75 microseconds

The extra credit questoin is left to other BRI members as an exercise of
their memory.

Roger Kirk