I will have to find the link, but last night I was digging around in
their
technical archives and I found a statement to the effect:"All domestic
AM BCB transmitters shall use a 75Us preemphaisis." I was looking
for the maximum analog BW a AM/MW station could use."

In the good old days class A stations could go with, I think up to
15KHz BW. I didn't feel like going to my parents and digging
through the 1955~1970 Popular Electroncs that had an article
on this issue.

I am trying to decide if I want to add a ~10KHz ceramic filter to
my outboard detector.
My fitler line up lloks like it will be:
500HZ crystal filter
2.1KHz crystal filter
3.8KHZ ceramic filter
5KHz ceramic filter
8 or 10KHz ceramic filter
(15KHz crystal filter for FM only!).
The FM will be designed and added later.

The audio will have 2 tilt tone control sections,
similar but with different pivot points. The first
centered at 700, the 2nd at ~1.4KHz. I hope to
decide if I can use one fitler with an ocatave
function, or if 2 fitlers in series will be better.
I would like to keep this simple enough for
someone other then me to use.

I am leaving the original audio chain in the R2000s
intact so that at there very least my wife will able to
use the "listening post".

A friend bought some "exotic" eletronic stuff from a
local engineering firm that went out of business.
Amoung the items were several NEDSP DSP
modules. See:
http://www.bhinstrumentation.co.uk/html/nedsp1061.html
I am trying to trade him out of at least one.
They are tiny, powerfull and don't mangle the audio
"too" much.

My "simple" outboard detector is undergoing
"mission creep".

Terry

wrote in message
oups.com...
I will have to find the link, but last night I was digging around in
their
technical archives and I found a statement to the effect:"All domestic
AM BCB transmitters shall use a 75Us preemphaisis." I was looking
for the maximum analog BW a AM/MW station could use."

My information might be outdated. Subjectively, though, I think I hear
differences in different stations. I suppose other factors in the
processing might account for any differences.



In the good old days class A stations could go with, I think up to
15KHz BW. I didn't feel like going to my parents and digging
through the 1955~1970 Popular Electroncs that had an article
on this issue.

I'm almost certain that's true. Even 10 kHz of good audio isn't bad, but I
don't hear much of that nowadays.



I am trying to decide if I want to add a ~10KHz ceramic filter to
my outboard detector.

That only allows 5 kHz for normal DSB AM. Will you be limiting the wideband
demodulation to the sync detector?


[snip]

Frank Dresser

On Sun, 26 Jun 2005 18:33:04 GMT, "Frank Dresser"
wrote:

Sec. 73.44 AM transmission system emission limitations.



(a) The emissions of stations in the AM service shall be attenuated
in
accordance with the requirements specified in paragraph (b) of this
section. Emissions shall be measured using a properly operated and
suitable swept-frequency RF spectrum analyzer using a peak hold
duration of 10 minutes, no video filtering, and a 300 Hz resolution
bandwidth, except that a wider resolution bandwidth may be employed
above 11.5 kHz to detect transient emissions. Alternatively, other
specialized receivers or monitors with appropriate characteristics
may
be used to determine compliance with the provisions of this
section,
provided that any disputes over measurement accuracy are resolved
in
favor of measurements obtained by using a calibrated spectrum
analyzer
adjusted as set forth above.

(b) Emissions 10.2 kHz to 20 kHz removed from the carrier must be
attenuated at least 25 dB below the unmodulated carrier level,
emissions 20 kHz to 30 kHz removed from the carrier must be
attenuated
at least 35 dB below the unmodulated carrier level, emissions 30
kHz
to 60 kHz removed from the carrier must be attenuated at least [5 +
1
dB/kHz] below the unmodulated carrier level, and emissions between
60
kHz and 75 kHz of the carrier frequency must be attenuated at least
65
dB below the unmodulated carrier level. Emissions removed by more
than
75 kHz must be attenuated at least 43 + 10 Log (Power in watts) or
80
dB below the unmodulated carrier level, whichever is the lesser
attenuation, except for transmitters having power less than 158
watts,
where the attenuation must be at least 65 dB below carrier level.

(c) Should harmful interference be caused to the reception of other
broadcast or non-broadcast stations by out of band emissions, the
licensee may be directed to achieve a greater degree of
attentuation
than specified in paragraphs (a) and (b) of this section.

http://kauko.hallikainen.org/FCC/FccRules/2005/73/44/

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

Anytime Terry!

Pete

wrote in message
oups.com...
Petet thanks for jumping in. I found this refference while searching
the FCC archive. I thought it was wrong, but just wanted to verify it.

Terry

"Pete KE9OA"
As far as AM receivers, they do not have a deemphasis circuit
following the detector. With FM receivers, it is a different story.
___________

But in effect, almost every AM receiver has de-emphasis -- it is the result
of the "haystack" amplitude response of their RF/IF circuits driving the 2nd
detector. Higher modulating frequencies are rolled off, sometimes very
severely.

The problem with trying to compensate for it at the AM tx is that the amount
needed for "flat" system response varies considerably from rx to rx, and
even with carrier frequency. Even so, many MW/SW AM stations do boost their
highs, trying to get some of it to pass through the narrowband receivers
typically in use these days.

RF

Frank Dresser wrote:

That only allows 5 kHz for normal DSB AM. Will you be limiting the
wideband
demodulation to the sync detector?

[snip]

Frank Dresser
---------------------------------------
I meant 20KHz for 10KHz recovered audio bandwidth.
I have some nice, but wide older Murata ceramics I salvaged
30 years ago from a (then) high end Kenwood tuner AM section.
I have them in a 35mm film cansiter labled 10KHZ. Sorry for
the sloppy thinking. It had a wide/HiFi positions as well as a
naorrow/distant positon. The "narrows" are like barn doors,
maybe 14~15 wide fora 6~7KHz signal, and the "wides" are
~21 wide giving just over 10KHz.

In a way it will be nice to use all this junk I have saved for the
last 3 decades.

Terry

Let's try that again.............AM receivers don't have a deemphasis
circuit. You can state that the composite response of an AM receiver implies
a deemphasis circuit, but that is not really true if you consider a
deemphasis circuit as having a standard turnover frequency and a standard
rolloff characteristic (so many dB per octave). (I do understand your point,
though).
A deemphasis circuit, as applied after the detector in FM receivers is
designed to have a specific rolloff characteristic that is the complement of
the preemphasis characteristic applied at the transmitting end.
This holds true for broadcast stations as well as land mobile equipment.
Take a look at any of the more recent stereo FM tuners/receivers and you
will see that this characteristic is determined by the external components
in the line amp of the stereo decoder chip.
A TDA1591 data sheet gives a good example of this circuit.
And you are right.....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.

Pete

"Richard Fry" wrote in message
...
"Pete KE9OA"
As far as AM receivers, they do not have a deemphasis circuit
following the detector. With FM receivers, it is a different story.
___________

But in effect, almost every AM receiver has de-emphasis -- it is the
result of the "haystack" amplitude response of their RF/IF circuits
driving the 2nd detector. Higher modulating frequencies are rolled off,
sometimes very severely.

The problem with trying to compensate for it at the AM tx is that the
amount needed for "flat" system response varies considerably from rx to
rx, and even with carrier frequency. Even so, many MW/SW AM stations do
boost their highs, trying to get some of it to pass through the narrowband
receivers typically in use these days.

RF

wrote:

I meant 20KHz for 10KHz recovered audio bandwidth.
I have some nice, but wide older Murata ceramics I salvaged
30 years ago from a (then) high end Kenwood tuner AM section.
I have them in a 35mm film cansiter labled 10KHZ. Sorry for
the sloppy thinking. It had a wide/HiFi positions as well as a
naorrow/distant positon. The "narrows" are like barn doors,
maybe 14~15 wide fora 6~7KHz signal, and the "wides" are
~21 wide giving just over 10KHz.

In a way it will be nice to use all this junk I have saved for the
last 3 decades.

Terry


If you have access to a spectrum analyser you can see what the
transmitted bandwidth is for some stations. You will find that many
transmit a lot more than what most radios pass.

For a real shock, look at the spectrum of an AM station transmitting
IBOC. You will want to have a narrow filter available to avoid passing
the digital hash.

craigm

"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.