"Michael R. Kesti" wrote in message
...
Karl Uppiano wrote:

The station was KCID AM in Caldwell, ID. 1490KHz/1KW. I worked there from
1978 to 1986. I don't think it's there anymore.

Google indicates otherwise, unless the pages it finds are out of date.

I just said I didn't know. If KCID is still in Caldwell and operating,
that's great. I haven't been back there for nearly 15 years, and I didn't
bother to Google it.

When I took it over, the
studio-transmitter link was 5KHz telephone lines. One of my first projects
was to install a microwave STL which gave us 15KHz bandwidth end-to-end.
Then I spent considerable effort bringing the entire audio chain up to FM
specs. My goal was to pass an FM audio proof of performance on an AM
station, and the management at the time supported this goal. We met this
goal for all of the parameters that were applicable to AM. Noise and
distortion were the most difficult parameters to keep in spec.

AM stations in the standard broadcast band are limited to 10 Khz
modulation
bandwidth and therefore to 5 Khz audio bandwidth. It would seem, then,
that
your station was in violation of bandwidth limitations.

Not at the time. The NRSC *10-KHz AUDIO* bandwidth limitation and
pre-emphasis was introduced in the early '90s. Prior to that, AM stations
were required to transmit a minimum 5 KHz audio bandwidth, and an
unspecified maximum audio bandwidth. We were required to check for spurious
emissions at 20KHz removed from our assigned frequency, which pretty much
says we could modulate all the way out to 20 KHz (if we could do it cleanly)
prior to the early '90s.

In the US, AM stations are allocated every 10KHz, which means that sidebands
from adjacent stations modulating above 5KHz will overlap, causing "monkey
chatter". That is why nearby stations are allocated on alternate channels
(20KHz apart), in which case they will only overlap if they exceed 10 KHz.
Even then, the interference is minimal, since non-pre-emphasized high
frequency energy is very low. Even in large markets, there are enough second
adjacencies that 40 KHz carrier spacing is often possible. Sideband
interference is much more noticeable at night, but even then, you are likely
to hear the 10KHz tones from the adjacent channel carriers and on-channel
interference than actual sideband overlap.

The NRSC standard added high-frequency pre-emphasis (similar to FM) in an
attempt to overcome the narrowband performance of consumer grade AM
receivers, and simultaneously placed an upper limit of 10KHz on all AM
stations in an attempt to keep the pre-emphasis from causing too much
adjacent channel monkey-chatter. So today, it is no longer possible to
achieve FM quality sound on AM. It is probably a reasonable compromise,
given the poor quality of AM receivers, and the fact that most AM
programming is all talk. But it is technically feasible, and we proved it on
a daily basis for several years in the early 1980s.

--
================================================== ======================
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
mrkesti at comcast dot net | - The Who, Bargain