I guess that I must be in the minority - it seems to me that for best AM
fidelity (not selectivity, nor sensitivity), you would use a crystal set
with tuned RF stages, no IF, no heterodyne of any kind. use the tubes for
RF amps if needed, and for audio amplification, and use a tube diode for the
detector.

In article ,
Patrick Turner wrote:

Syl's Old Radioz wrote:

"Patrick Turner" a écrit dans le message

I don't expect anyone to pay 3c for what I say, which could be
seen as OT.

You just met our village idiot it seems...

There is an unspoken rule here..._Ignore_ his posts. Let him talk
to himself.

We don't get into fight with village idiot like you do on
RAT...Keeps rar+p "clean"...;o)

Syl

Well, with all due respects to all gentlemen and possible idiots on
all groups to whom this subject thread is cross posted to, I reserve
the right to decide who I will ignore or not.

I will desperately try not step on anyone's toes as I act in well
intentioned freewill.

I won't budge from the idea that its possible to digitise the signal
from the antenna and simply apply suitable algorithms, and get
digital decoding, without all the phase shift caused by consecutive
tuned circuits.


Chill dude. There is nothing wrong with this idea and the current
technology can do it. The problem is money. It would be expensive to do
this and I would not expect people to pay the price when it would be a
small improvement over the current generation of radios. Heck, I would
not expect people to pay the price for a large improvement.

Digital techniques do not end all distortion and add there own type of
noise by the way.

--
Telamon
Ventura, California

william_b_noble wrote:

I guess that I must be in the minority - it seems to me that for
best AM fidelity (not selectivity, nor sensitivity), you would use a
crystal set with tuned RF stages, no IF, no heterodyne of any kind.
Use the tubes for RF amps if needed, and for audio amplification,
and use a tube diode for the detector.

Actually, this setup intrigues me for local reception, since it
appears to be a quite simple circuit. Are there any schematics of such
a circuit -- any commercially made radio of yesteryear using this
design approach?

Jon

John Byrns wrote:

1. It has been variously stated that the audio bandwidth of AM
broadcasting is either 3.5 kHz, 5 kHz, or 10 kHz. In the US AM broadcast
channels are 20 kHz wide, so audio is effectively limited to a maximum of
10 kHz by law/regulation. It is my impression that most AM stations
transmit audio out to this legal maximum. Of course as HD-radio takes
hold this will change with the analog signal cutting off somewhere around
5 kHz. I know there are at least 2 active broadcast engineers that read
this group, perhaps they could fill us in on what the stations they are
involved with are actually doing as far as audio bandwidth goes?


We've kicked this around the block before - but I guess it won't hurt to
kick it one more time. (I'm only going to address US standards here).

The AM Bandwidth is 10Khz.
However - what has to be taken into consideration are "real world"
filters - and the "stop band" specifications of the NRSC-1. I.E. the
signal must be down 15db (from 100% modulation) AT 10khz(!!!)

Further - it must be:
-30db at 10.5Khz;
-40db at 11Khz; and
-50db at 15Khz.
-50db is .32% modulation (that's point 32 percent - not 32 percent).

Now - depending on how good your processor / final filters are - figure
your "real world" bandwidth from there. Consider "good" filters at 12db
per octave - and "really, really good" filters at 24db per octave (an
octave is 1/2 (going down) or double (going up) a given frequency.

So if you put a 12db per octave filter in front of your transmitter -
the highest unattenuated frequency through that filter will be around
4.5Khz.

You can do much better with a 24db per octave - somewhere around 7.5Khz.
Of course - NRSC-1 is no longer the "newest kid on the block" - the
new one is ITU-R (Recommendation 328-5). To meet that spec. - the
processor filters are set to 6.0Khz.

Amigos and Optimods are set up to meet NRSC-1 power spectrum
requirements "out of the box". The Optimod 9200 (the current top of the
line digital AM processor) is adjustable from 4.5kHz to 9.0kHz in 0.5kHz
steps, plus NRSC - is guaranteed to meet ITU-R (Recommendation 328-5)
and NRSC-1 power spectrum specifications without the need for further
low-pass filtering prior to the transmitter. And as noted -- is
typically set for 6.0kHz for ITU-R.

Amigos or Optimods are probably in 90%+ AM stations in the US (We're
(WMER) is running an Amigo).

Here is the NRSC site for those wishing to get thoroughly tech:

http://www.nrscstandards.org/

And NRSC-1 itself (PDF document - needs acrobat reader)

http://www.nrscstandards.org/nrsc-1.pdf

2. The idea expressed above that a "modern sophicated decompressor
circuit could match the curve of the compressor" seems far fetched to me.

Yeah, I agree: I can't imagine trying to "undo" what either the Optimod
or the Amigo do to the audio; talk about multi-band; mutli-limit;
multi-everything... sheesh.

Here's Orban's Optimod 9200:

http://www.orban.com/orban/products/..._overview.html

You'll find a pop-up menu in the upper right of the page - you can view
the features and specs. from there. Impressive stuff.


best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

In article , Patrick Turner
wrote:

John Byrns wrote:

7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to see why
this should be true.

Because for the same Q value, the pass band would be 4 times wider

Where is it written that the same loaded Q must be used for both filters?
If you can change the center frequency, why can't you change the loaded Q?

Within reason, for bandwidths typical of audio
receivers, you should be able to build a filter at 455 kHz that has
effectively the same response as a 2 MHz filter. There is no need to
throw out the 455 kHz IF just to get wide bandwidth.

Its difficult to make a 455kHz typical old IFT produce a nice flat topped
20 kHz wide BW. Its either pointy nosed, undecoupled, or flat topped, critical
coupled,
or over critical or rabbit eared.
I have tried all that.

So you have tried all that and rejected the "pointy nosed", "flat topped",
and "rabbit eared" response curves. I am left to wonder what sort of
response curve you were looking for? Why not settle for a nice "flat
topped" response curve and be done with it?


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article , wrote:

John Byrns wrote:

1. It has been variously stated that the audio bandwidth of AM
broadcasting is either 3.5 kHz, 5 kHz, or 10 kHz. In the US AM broadcast
channels are 20 kHz wide, so audio is effectively limited to a maximum of
10 kHz by law/regulation. It is my impression that most AM stations
transmit audio out to this legal maximum. Of course as HD-radio takes
hold this will change with the analog signal cutting off somewhere around
5 kHz. I know there are at least 2 active broadcast engineers that read
this group, perhaps they could fill us in on what the stations they are
involved with are actually doing as far as audio bandwidth goes?


We've kicked this around the block before - but I guess it won't hurt to
kick it one more time. (I'm only going to address US standards here).

The AM Bandwidth is 10Khz.
However - what has to be taken into consideration are "real world"
filters - and the "stop band" specifications of the NRSC-1. I.E. the
signal must be down 15db (from 100% modulation) AT 10khz(!!!)

Further - it must be:
-30db at 10.5Khz;
-40db at 11Khz; and
-50db at 15Khz.
-50db is .32% modulation (that's point 32 percent - not 32 percent).

Now - depending on how good your processor / final filters are - figure
your "real world" bandwidth from there. Consider "good" filters at 12db
per octave - and "really, really good" filters at 24db per octave (an
octave is 1/2 (going down) or double (going up) a given frequency.

So if you put a 12db per octave filter in front of your transmitter -
the highest unattenuated frequency through that filter will be around
4.5Khz.

You can do much better with a 24db per octave - somewhere around 7.5Khz.
Of course - NRSC-1 is no longer the "newest kid on the block" - the
new one is ITU-R (Recommendation 328-5). To meet that spec. - the
processor filters are set to 6.0Khz.

Amigos and Optimods are set up to meet NRSC-1 power spectrum
requirements "out of the box". The Optimod 9200 (the current top of the
line digital AM processor) is adjustable from 4.5kHz to 9.0kHz in 0.5kHz
steps, plus NRSC - is guaranteed to meet ITU-R (Recommendation 328-5)
and NRSC-1 power spectrum specifications without the need for further
low-pass filtering prior to the transmitter. And as noted -- is
typically set for 6.0kHz for ITU-R.

Amigos or Optimods are probably in 90%+ AM stations in the US (We're
(WMER) is running an Amigo).

OK, now we are getting down to brass tacks as my Grandmother used to say,
whatever that may mean. The $64 question is does the Amigo as used at
WMER only do NRSC, or does it have a selection of cutoff frequencies like
the Optimod 9200, and if it does what is the cutoff frequency set to at
WMER?


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

Randy,

You get the award for most informative post concerning the "broadcast
standards" in this thread. I was waiting for you to come through. It
takes someone with real broadcast experience to give us the real scoop.
Thanks.

Phil B

"Randy and/or Sherry" wrote in message
...


John Byrns wrote:

1. It has been variously stated that the audio bandwidth of AM
broadcasting is either 3.5 kHz, 5 kHz, or 10 kHz. In the US AM
broadcast
channels are 20 kHz wide, so audio is effectively limited to a
maximum of
10 kHz by law/regulation. It is my impression that most AM stations
transmit audio out to this legal maximum. Of course as HD-radio
takes
hold this will change with the analog signal cutting off somewhere
around
5 kHz. I know there are at least 2 active broadcast engineers that
read
this group, perhaps they could fill us in on what the stations they
are
involved with are actually doing as far as audio bandwidth goes?


We've kicked this around the block before - but I guess it won't hurt
to
kick it one more time. (I'm only going to address US standards here).

The AM Bandwidth is 10Khz.
However - what has to be taken into consideration are "real world"
filters - and the "stop band" specifications of the NRSC-1. I.E. the
signal must be down 15db (from 100% modulation) AT 10khz(!!!)

Further - it must be:
-30db at 10.5Khz;
-40db at 11Khz; and
-50db at 15Khz.
-50db is .32% modulation (that's point 32 percent - not 32 percent).

Now - depending on how good your processor / final filters are -
figure
your "real world" bandwidth from there. Consider "good" filters at
12db
per octave - and "really, really good" filters at 24db per octave (an
octave is 1/2 (going down) or double (going up) a given frequency.

So if you put a 12db per octave filter in front of your transmitter -
the highest unattenuated frequency through that filter will be around
4.5Khz.

You can do much better with a 24db per octave - somewhere around
7.5Khz.
Of course - NRSC-1 is no longer the "newest kid on the block" - the
new one is ITU-R (Recommendation 328-5). To meet that spec. - the
processor filters are set to 6.0Khz.

Amigos and Optimods are set up to meet NRSC-1 power spectrum
requirements "out of the box". The Optimod 9200 (the current top of
the
line digital AM processor) is adjustable from 4.5kHz to 9.0kHz in
0.5kHz
steps, plus NRSC - is guaranteed to meet ITU-R (Recommendation 328-5)
and NRSC-1 power spectrum specifications without the need for further
low-pass filtering prior to the transmitter. And as noted -- is
typically set for 6.0kHz for ITU-R.

Amigos or Optimods are probably in 90%+ AM stations in the US (We're
(WMER) is running an Amigo).

Here is the NRSC site for those wishing to get thoroughly tech:

http://www.nrscstandards.org/

And NRSC-1 itself (PDF document - needs acrobat reader)

http://www.nrscstandards.org/nrsc-1.pdf

2. The idea expressed above that a "modern sophicated decompressor
circuit could match the curve of the compressor" seems far fetched
to me.

Yeah, I agree: I can't imagine trying to "undo" what either the
Optimod
or the Amigo do to the audio; talk about multi-band; mutli-limit;
multi-everything... sheesh.

Here's Orban's Optimod 9200:

http://www.orban.com/orban/products/..._overview.html

You'll find a pop-up menu in the upper right of the page - you can
view
the features and specs. from there. Impressive stuff.


best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

John Byrns wrote:
In article , Patrick Turner
wrote:


John Byrns wrote:


7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to see why
this should be true.

Because for the same Q value, the pass band would be 4 times wider


Where is it written that the same loaded Q must be used for both filters?
If you can change the center frequency, why can't you change the loaded Q?

Admittedly it might be a bit more difficult to achieve the same Q at 2
MHz as 455 but we are talking about homebrewing and experimenting here.



Its difficult to make a 455kHz typical old IFT produce a nice flat topped
20 kHz wide BW. Its either pointy nosed, undecoupled, or flat topped, critical
coupled,
or over critical or rabbit eared.
I have tried all that.


So you have tried all that and rejected the "pointy nosed", "flat topped",
and "rabbit eared" response curves. I am left to wonder what sort of
response curve you were looking for? Why not settle for a nice "flat
topped" response curve and be done with it?

Here's a wacky idea that I'll toss out just to see if it flies...

Could one use two garden variety 455kc xfmrs in series, one tuned at
center plus and the other tuned center minus? Impedance matching would
be an issue but maybe such a scheme offers a not so glamourous method of
achieving the wider bandwidth and maintaining the flatness with little ado.

Re wider bandwidth as a whole. On AM sets that I have owned with
excessively wide bandwidth they all tend to sound like crap. I don't
have a wealth of local stations that might be enhanced by the wider
width but on weaker stations the amount of noise and all those AM
"artifacts" seems to go way up making it very unpleasant to listen to.

As a result I think it would make the most sense to use a switchable or
continuously variable bandwidth scheme so as to not be left with an all
or none scenario after so much effort.

John B, you may remember one of my Tandberg receivers that had 4
positions of bandwidth ganged with a switch that somewhat tailored the
audio accordingly. To the ear (or rather to my ear) this seemed very
effective.

-Bill M

Now - depending on how good your processor / final filters are - figure
your "real world" bandwidth from there. Consider "good" filters at 12db
per octave - and "really, really good" filters at 24db per octave (an
octave is 1/2 (going down) or double (going up) a given frequency.


Randy, those figures are not characteristic of modern processors that
use DSP filtering, which is capable of extremely rapid rolloff.

Take a look at http://n2.net/k6sti/speech.jpg . This is a screen shot
of my HP 141T/8553B/8552B spectrum analyzer tuned to a local AM radio
station broadcasting speech. The analysis-filter bandwidth was 300 Hz,
the vertical scale 10 dB/div, and the horizontal scale 5 kHz/div. I
set the storage-screen persistence to maximum and accumulated spectra
for 10-15 seconds. It is easy to see the extremely sharp rolloff at 10
kHz. http://n2.net/k6sti/music.jpg shows a different AM station
broadcasting classical music. The music spectrum is evident, but so is
the brick-wall filtering at 10 kHz. These spectra are typical of what
I observe for AM stations here in Southern California.

If you have a receiver capable of SSB reception, you can easily check
the spectral limits of any AM station. Put the receiver in LSB mode
and tune down frequency from the carrier (or use USB and tune up).
Regardless of program content, it will be obvious where the response
ends. You'll hear the modulation sidebands suddenly vanish. Whenever
I've tried this, my dial has always read more than 9 kHz away from the
carrier.

Brian

Patrick Turner wrote:
Volker Tonn wrote:
Jon Noring schrieb:

In the last couple of years I've posted various inquiries to this and
related newsgroups regarding high-performance, tube-based AM (MW/BCB)
tuners, both "classic" and modern.

Have a look into the "Collins" S-series. These are state-of-the-art
tube sets 'til now. At least it's not the tubes alone but the fabulous
mechanical IF-filters giving outstanding results for a tube set.
Manuals with layout diagrams should be available on the web....

Since Mr Noring says he has regularly trawled the Net for everyone
else's expertise on AM reception, but got nowhere, because he's
still doin it, why doesn't he gird his loins and put his shoulder to
the task of learning all about AM and radio engineering as spelled
out so clearly in all the old text books, and then damn well build
his own perfect AM radio???

Thanks for sharing your frank coments. They are acknowledged.

The important thing is that the replies to my "trawling" have been
very informative, including yours Patrick, and are not only
benefitting me, but are benefitting many others who are following this
thread in real time.

Whether my trawling is successful or not for my purposes is immaterial
-- if I fail, I fail -- I don't fear failure as some do -- the
discussion is further adding to the information pool for the community
of those interested in some aspect of tube-based AM tuners, and in
that regards I think it has been successful. (With Google archiving
the newsgroups, this information is now being preserved, and is
searchable.)

There are obviously two sides to the engineering of radio receivers:
1) the basic theory and the basic categories of design approaches
(which I am studying -- it helps in that back in 1974 I had the
equivalent of one years' worth of basic electrical engineering courses
at the University of Minnesota, which is now all coming back to me),
and 2) the real-world engineering of receivers/tuners, using real
rather than theoretical components, and the attendant compromises and
work-arounds which inevitably result.

I do agree with Patrick's implying that there is no such thing as a
"perfect radio". I am not seeking the "perfect radio", but a
modern-design tuner "kit" sufficiently meeting the various
requirements I have previously set forth. I believe once a good
design results, that PCB boards can be made, coils can be built by
someone or some company experienced in doing that (I mention coils
since that is the one component difficult to buy right off the shelf
-- thank god no one has to build their own tubes!), and the schematic
with detailed instructions and guidelines sold through diytube (as an
example.)

The target market for the "kit" are those who build their own tube-
based components for their audio system, and want every component to
be a high-performer, approaching audiophile-grade in performance (yes,
AM broadcasts are not "audiophile", but audiophiles want a tuner that
brings out the best in what is there in the signal.) They don't want
to spend their limited time building junk, they don't want to build a
Radio Shack beginners' crystal set. They want very good performance
(which is admittedly a "fuzzy" word), commensurate with their other
components. They just want the tuner kit not to be overly complicated
in design, to work if they follow the instructions and guidelines, and
to meet their (collective) expectations.

And these kit builders are not novices, either, at wielding a
soldering gun, and in chassis and cabinet design -- they are
mechanically- and electronically-inclined, and are now building
audiophile-grade amps and preamps from the many kits now out there. I
also believe that some of the vintage radio collectors, who are
experienced at restoring radios, will also take an interest in the AM
tube tuner kit. (For those who don't know, I'm now restoring a Philco
37-670 console, so I'm not exactly out-of-touch with the radio
collecting world.)

Based on my experience with building audiophile-grade tube amps and
plugging into that community, I think I've laid out pretty well what
they want and expect. Most are not going to become radio design
enthusiasts, they will not live and breathe tuners, building hundreds
of circuits on cake pans in their basement (and I am not disparaging
those who do!) They simply are going to listen to the tuner they
laboriously built from the kit, happy with its performance, and happy
for what they have learned about how radios work "under the hood", in
a general sense. Some will no doubt get the radio bug, and join the
people here, rescuing old radios from the landfill, and restoring
them.

Maybe my focus on TRF-based designs and "channel-based design" have
been diversions. But, from what I've read about real-world TRF designs
(John Byrns messages have been great here), a TRF-based design has
some nice attributes from the audiophile kit perspective, and there
are clever real-world solutions around the selectivity and gain
limitations of the "what's taught in textbooks" regarding basic TRF
design, as John Byrns and others have noted many many times, but which
seems to fall on deaf ears of those who believe that the best
high-performance receiver (however "high-performance" is defined)
*must* be super-het in basic design.

But obviously, the vast majority of commercial designs of
high-performance tube-based radio receivers from the mid 1930's to the
1950's are super-het designs, and many of them are great performers,
so I'll post a parallel message with another call for candidate radios
to inspire the AM tuner kit. After all, if one is to put together an
AM tube tuner kit, it makes a lot of sense to base it on a proven
design from the past -- why reinvent the wheel?

For example, diytube (at http://www.diytube.com/ ) has taken the
venerable Dynaco ST-35 amp design, modernized it some (and to further
improve its audiophile performance), and is now selling the PCB
board with schematics and instructions to diy audiophiles. it is an
excellent performer (I know firsthand -- it is a *very nice* sounding
amp.) diytube is now working on a high-power monoblock tube amp kit
based on the Eico EL34 amp of old -- can't wait until it is released.

Just some thoughts...

Jon Noring