"Pete KE9OA"
....it would be very difficult to have a standard preemphasis curve for AM
stations, because there are so my receivers with different characteristics
because of different I.F. bandwidths and different rolloff characteristics
in the audio chain.
______________

In the US, broadcast AM pre-emphasis is defined by a voluntary standard of
the Nat'l Radio Systems Committee. The tx audio response is a modified 75
us curve. The curve has an 8700 Hz break frequency to reduce adjacent
channel interference.

The NRSC standard expects the amplitude response of the narrow RF/IF
bandwidth of "typical" MW broadcast receivers to restore ~ flat system
response, not that a network complementary to that at the tx be added to
audio circuits following the 2nd detector. However that is not
prohibited -- it is just more expensive. Also, that approach to
implementing AM pre/de-emphasis would not be "backward compatible."

RF (retired broadcast field/systems engineer -- RCA & Harris Corp)

Visit http://rfry.org for FM transmission system papers.

I agree...............still, you don't see a deemphasis network actually
following the detector in AM receivers. Are there many stations actually
using the curve?

Pete

"Richard Fry" wrote in message
...
"Pete KE9OA"
....it would be very difficult to have a standard preemphasis curve for AM
stations, because there are so my receivers with different characteristics
because of different I.F. bandwidths and different rolloff characteristics
in the audio chain.
______________

In the US, broadcast AM pre-emphasis is defined by a voluntary standard of
the Nat'l Radio Systems Committee. The tx audio response is a modified 75
us curve. The curve has an 8700 Hz break frequency to reduce adjacent
channel interference.

The NRSC standard expects the amplitude response of the narrow RF/IF
bandwidth of "typical" MW broadcast receivers to restore ~ flat system
response, not that a network complementary to that at the tx be added to
audio circuits following the 2nd detector. However that is not
prohibited -- it is just more expensive. Also, that approach to
implementing AM pre/de-emphasis would not be "backward compatible."

RF (retired broadcast field/systems engineer -- RCA & Harris Corp)

Visit http://rfry.org for FM transmission system papers.

"Pete KE9OA"
Are there many stations actually using the curve?

Probably at least 1/2 of them are (there's no official record that I know
of).

Nice website!

Thanks.

RF

Nice website!

Pete

"Richard Fry" wrote in message
...
"Pete KE9OA"
....it would be very difficult to have a standard preemphasis curve for AM
stations, because there are so my receivers with different characteristics
because of different I.F. bandwidths and different rolloff characteristics
in the audio chain.
______________

In the US, broadcast AM pre-emphasis is defined by a voluntary standard of
the Nat'l Radio Systems Committee. The tx audio response is a modified 75
us curve. The curve has an 8700 Hz break frequency to reduce adjacent
channel interference.

The NRSC standard expects the amplitude response of the narrow RF/IF
bandwidth of "typical" MW broadcast receivers to restore ~ flat system
response, not that a network complementary to that at the tx be added to
audio circuits following the 2nd detector. However that is not
prohibited -- it is just more expensive. Also, that approach to
implementing AM pre/de-emphasis would not be "backward compatible."

RF (retired broadcast field/systems engineer -- RCA & Harris Corp)

Visit http://rfry.org for FM transmission system papers.