Hi Frank,

I didn't realize that..........I thought that the older AM stations took
greater pains to have flatter high frequency response. I do remember
listening to stations such as WGN on my old McIntosh MR-55, and they sounded
very good. The same stations on my Dynaco AF-6 tuner in its wide bandwidth
sounded shrill, as you describe.
As far as AM receivers, they do not have a deemphasis circuit following the
detector. With FM receivers, it is a different story.
Thanks for the info!

Pete

"Frank Dresser" wrote in message
...

"Pete KE9OA" wrote in message
...

[snip]

AM stations do not use any preemphasis so a deemphasis network after the
detector in your receiver is not required.

It's my understanding that there's no FCC standard for AM stations to
preemphasize their audio, but nearly all do in order to compensate for the
normal roll off. I have an old school high fidelity AM receiver, and AM
stations usually sound rather shrill on the "Hi-Fi" IF bandwidth position.

A quick google search brings up:

"In 1977 Orban Associates introduced "Optimod-AM." This unit contained a
high-slope receiver equalizer to pre-compensate for the highly rolled-off
radios of the time, "

http://www.bext.com/histproc.htm

"and Omnia exclusives like a pre-emphasis section placed behind the
multi-band limiters to create a more consistent, natural sound."

http://www.omniaaudio.com/am.htm


It is true that digital modes such as IBOC are being use on the MW band,
but
this is a totally different technique.

Pete


I brought up IBOC because Clear Channel wants all AM radio stations to
limit
their audio bandwidth to 5 - 6 kHz. One of the reasons for the change was
given:

"1. Increased modulation efficiency. By eliminating the broadcast of the
high-frequency energy, we can increase the amount of energy that is in the
20 Hz to 5 kHz region. Let's not forget that due to pre-emphasis, higher
frequencies are boosted and will have a more profound effect on total
modulation than lower frequencies will."

http://www.rwonline.com/reference-ro...andwidth.shtml

I don't know if the IBOC stations use a different preemphasis on the
analog
channel than the non IBOC stations.

Frank Dresser