To get good AM reception,
the AF bw should at least be 15kHz, and the SNR
at -60 dB, about only possible with local stations,
and with a N&D at around -60dB for the electronics.

This isn't very easy to attain, without some rather
special circuit techniques somewhat better than those used
by a simple 6AN7/6BE6 mixer tube,
and a pair of critically coupled standard IFTs,
with a 6N8/6BA6 IF amp, and a germainium diode
powered of the secondary of the 2nd IFT.
This is what is used with a normal 2 tube AM tuner on may
standard old radios, often designed to have only 5 kHz of af bw..
Nearly all these old superhets have one tuned circuit before the mixer,
and a total of 4 tuned circuits at 455 kHz in the IFTs.
This gives sufficiently steep rates of attenuation outside
the IF bw.
In each IFT, the two coils are loosely coupled,
ie, not tightly coupled like an AF tranny, and because the P
and S windings are tuned with a cap for 455 kHz, they act differently to

an AF tranny, and with the two coils well apart, the
Q of the output signal can be very high, so that the BW
is as low as 4.55 kHz.
But as the coils are brought closer, there is a critical
setting where the sharp peaked nose shape of the bandbass character
becomes flat across the top, and the BW is perhaps 10 kHz,
allowing sidebands of RF +/- 5 kHz either side of 455 kHz,
and the resulting AF bw is 5 kHz.
The fuller explanation of way IFTs are usually constructed and set
up are in RDH4, and many other old books.
Reducing the distance between the two IFT coils produces a
response that has two peaks, with a dip between the two,
and the IFT is said to be over critically coupled.
Sometimes the 1st IFT operating off the mixer is set up like this
and its bw can be more than 10 kHz, and set up to compensate
for the 2nd IFT, which has a flat topped shape,
so that the final AF response is slightly wider, and compensated
for the loses one gets with cascaded IF stages
Also in RDH4 is the method of using a tertiary winding of a few turns
in series with the S winding, which are them wound around the
P of the IFT, and this extends the AF bw. It often is switched,
so tuning is done with narrow band set, then the tertiaries switched in
for hi-fi, but usually not much more than 8 kHz is available.
RDH4 also has the details of such arrangements.
Some careful adjustments of the Q of the IFTs is required to get
20 kHz BW, and perhaps its better to use 3 IFTs of
quite low Q tuned circuits, with low gain amps.

One such fairly well concieved Oz designed AM tuner
was the 1982 kit designed by John Clarke at ELECTRONICS Australia,
which was all SS, and which had a balanced input loop antenna,
fet RF amp, two fets used in a balanced fet mixer,
3 x IFTs, with two fet IF amps, and with IFTs which have a 27 pF
cap from the top of the P coil to the top of the S coil, which also
broadens
the IF bw, and hence the AF bw.

The local oscilator was a 2 x bjt + 1 x fet affair,
and the detector is a CA3100 with a diode in a FB circuit,
which should give far lower thd than a germanium diode driven off a
pentode circuit.
This had a switcable narrow band ceramic filter
There was also an opamp buffer off the detetor, an audio bw filter,
and another TLO72 buffer, driving a bridged T notch filter,
which has about 1.5 kHz wide band cut width, but about 40 dB
of attenuation at 9 kHz.
This is a brief description of what is a complex SS circuit,
but its cost would be low to the mass maker,
as all SS pcb boards are, compared to doing it all with tubes.
But tubes could be used, and I have used them,
and a biased diode detector driven by a CF tube
will produce very low thd at 90% modulation, even at 1v audio output
or less, and most certainly at 10v output.
A tube mixer is probably quite linear at the few mV at which it
operates,
and so would the balanced fet mixer, which we could expect to be
very quiet, so the use of an all fet RF input, and mixer
with all tubes might produce the very best result, if
we like playing with tubes.
The fets used were 2N5485, and like many fets don't have much more
Gm than a pentode, but they do have high Z input,
and high Rd, and are quiet, and their gain can be controlled by bias
applied from an AVC voltage also produced from the detector stage.
The Playmaster AM tuner had a 3 gain tuning cap,
6 canned tuning coils, 3 toroidal coils, 6 x fets and 2 x bjts,
and 6 x ICs.
I have never seen a sample of this tuner.

I would like to see the schematic of the AM100.

I dimly recall an earlier AM tuner schematic I had for an SS superhet,
from some other magazine, which boasted great performance.
Along with the Playmaster schematic I have,
I also have several versions on synchronous AM detectors, all
boasting about their wondrous performance,
but the tubed versions are difficult to make.

Patrick Turner.

Whatever happened to AM stereo anyway?

Henry007 wrote:

Whatever happened to AM stereo anyway?




Yeah. Seems to be dead in this town (New York City). I think
I may be the only listener here that owns a stereo AM receiver.
Which likely explains the lack of stations transmitting it. Rumor
had it would limit the range of an AM signal to ordinary AM radios....

Henry007 wrote:

Whatever happened to AM stereo anyway?

The AM band has become very crowded, with noise and interference
spoiling any distant station listening. many stations have limited audio

bw used to modulate their carriers to prevent interference from adjacent
stations,
so the signal transmitted can never be a hi-fi signal when recieved.

FM has become mainstream, economically more viable to transmit
and it is inherently quieter,
with af bw of 15 kHz, so AM has low interest to music listeners.
AM is good for talk back, where folks can argue via their mobile phones.

Patrick Turner.

"Patrick Turner"


The AM band has become very crowded,


** Not in Australia.

The AM station line up in Sydney is much the same as it was 50 years ago.


with noise and interference
spoiling any distant station listening.


** No chance of hi-fi there anyhow.



many stations have limited audio

bw used to modulate their carriers to prevent interference from adjacent
stations,


** Not the ones transmitting in Sydney or other capitals for sure.


so the signal transmitted can never be a hi-fi signal when received.


** More Turneroid rot blown out his bum.



FM has become mainstream, economically more viable to transmit
and it is inherently quieter,
with af bw of 15 kHz, so AM has low interest to music listeners.
AM is good for talk back, where folks can argue via their mobile phones.


** AM has several advantages technically over FM. The signal is not
prone to nasty multipath distortion, travels through brick walls with little
attenuation, does not need a high mounted directional antenna to avoid
constant signal drop outs and hence more distortion.

The rooftop antenna system installed where I am living now works well for
all the TV channels - but has no FM band signals available. They appears
to have been removed by a filter.

With only a small frame aerial sitting on the floor next to it the AM100
works well in my lounge room.



........... Phil

Phil Allison wrote:

"Patrick Turner"

The AM band has become very crowded,

** Not in Australia.

Foe many years we had 2XX at 300 watts only 45 kHz away from 2CA
at 5 kW on the Canberra AM band.
Only really good AM radios tuned to 2XX without 2CA in the background.
At night, other stations could be heard when tuned to 2XX.
2XX has since moved to the FM band.
Now we have the print handicapped station which has a very good
audio signal, also at 300 watts, but placed better, and it is interference free
on good sets.
There would be a lot less interference if the stations were spread further apart

and there were less stations.
What we have is the lowest common denominator.
I recall japan has even closer station spacing than 9 kHz.



The AM station line up in Sydney is much the same as it was 50 years ago.

I recently had to replace an old radio dial whose station markings
became dust and stated to fall off.
I purchased a copy of the list of Oz stations' F and call signs and
the number has doubled from 1953, so the original station dial markings were
useless,
so I calibrated a new dial with a sig gene, and drew up a template, scanned it,
and made an adhesive transparency for the dial glass, since
cheap pleasant technical extertise is plentiful in Canberra.
The owner of that STC radio was very happy with the job I did,
and found it easy to get to the local stations he wanted.
I was able to fit the SW band in easily.



with noise and interference
spoiling any distant station listening.

** No chance of hi-fi there anyhow.

And for all the detailed reasons I cited.



many stations have limited audio

bw used to modulate their carriers to prevent interference from adjacent
stations,

** Not the ones transmitting in Sydney or other capitals for sure.

so the signal transmitted can never be a hi-fi signal when received.

** More Turneroid rot blown out his bum.

The fellow who lives next door was an ABC engineer for many years,
and said bw limiting is used on many stations.

You are the only one with serious windy bum problems.



FM has become mainstream, economically more viable to transmit
and it is inherently quieter,
with af bw of 15 kHz, so AM has low interest to music listeners.
AM is good for talk back, where folks can argue via their mobile phones.

** AM has several advantages technically over FM. The signal is not
prone to nasty multipath distortion, travels through brick walls with little
attenuation, does not need a high mounted directional antenna to avoid
constant signal drop outs and hence more distortion.

Rubbish.
FM goes through brick walls here with no problems.
I get far better sound quality with FM even when using a plain
old 300 ohm folded loop of 300 ohm ribbon on a stick about 1.5 m long.
The signal strength IS variable with antenna alignment, and sure,
there are reflections, just like poor TV signals used to be with VHF,
but anyone using a decent FM antenna gets spendid reception
if line of sight is clear to the transmitter.


The rooftop antenna system installed where I am living now works well for
all the TV channels - but has no FM band signals available. They appears
to have been removed by a filter.

Well then install a better antenna of your own.
The extra trouble is worth the effort.
The programme content is grim on the AM band.



With only a small frame aerial sitting on the floor next to it the AM100
works well in my lounge room.

Its still not as good as a decent FM signal.

And the neworking of AM signals around the country mean
that the signal has gone through much electronics on its way around
prior to being transmitted.
Many times I have listened to Lucky Ocean speaking on his Nightly Planet
Radio National AM radio program, and his appalling voice is all the worse for
serious
limiting of the signal, and it explains the nasally tone heard so often.
The wave form seen on the CRO shows horrendous clipping, well
before the limits of the AM reciever are reached.
Only lipservice is paid to the AM fidelity.
Once FM came in, transmitted AM fidelity became rarer.

And on a decent AM tuner with at least 10 kHz of AF bandwidth,
and excellent dynamic range ability, the deficiencies of
the transmitted signal from many AM stations is all too obvious.

The text books say excellence IS possible from AM,
but its rarely ever seen.
We mainly all jumped onto the FM bandwagon.

The 1987 Ford Laser I drive has a standard supplied terrible quality AM/FM
receiver, poor snr, terrible audio, and very poor noise rejection
once outside city limits, and poor selectivity for both bands.

I do plan to change to a better set when funds permit,
and connect the sound outputs to a set of noise cancelling headphones,
to make a trip to Sydney which is 310 Kms a little less damaging to my hearing.

Patrick Turner.

"Patrick Turner" wrote in message
...


Phil Allison wrote:

"Patrick Turner"

The AM band has become very crowded,

** Not in Australia.

The AM station line up in Sydney is much the same as it was 50 years
ago.


I recently had to replace an old radio dial whose station markings
became dust and stated to fall off.
I purchased a copy of the list of Oz stations' F and call signs and
the number has doubled from 1953,


** There is not one major new station in Sydney in 40 years.

A few low powered ones that cause no issues only.



so the original station dial markings were
useless,


** There was a minor re-shuffle of spots when 9 kHz spacing came in.



with noise and interference
spoiling any distant station listening.

** No chance of hi-fi there anyhow.

And for all the detailed reasons I cited.


** Wrong - even if some distant station were the only one on the band
there is still too much fading day and night for serious use. Plus man made
noise that has existed for many decades, plus storms hundreds of miles away
etc will ruin the sound.



many stations have limited audio bw used to modulate their carriers to
prevent interference from adjacent
stations,


** Not the ones transmitting in Sydney or other capitals for sure.


so the signal transmitted can never be a hi-fi signal when received.


** More Turneroid rot blown out his bum.


The fellow who lives next door was an ABC engineer for many years,
and said bw limiting is used on many stations.


** Like I said - not the ones in Sydney or other capitals.


You are the only one with serious windy bum problems.


** You are nothing but a bum.



FM has become mainstream, economically more viable to transmit
and it is inherently quieter,
with af bw of 15 kHz, so AM has low interest to music listeners.
AM is good for talk back, where folks can argue via their mobile
phones.


** AM has several advantages technically over FM. The signal is not
prone to nasty multipath distortion, travels through brick walls with
little
attenuation, does not need a high mounted directional antenna to avoid
constant signal drop outs and hence more distortion.

Rubbish.


FM goes through brick walls here with no problems.


** Go measure the attenuation.


I get far better sound quality with FM even when using a plain
old 300 ohm folded loop of 300 ohm ribbon on a stick about 1.5 m long.


** In room FM antennas are very prone to signal drop outs for the same
reason the set top TV antennas give bad pictures.



The signal strength IS variable with antenna alignment, and sure,
there are reflections, just like poor TV signals used to be with VHF,
but anyone using a decent FM antenna gets splendid reception
if line of sight is clear to the transmitter.


** Which is just what I posted - you need a roof top antenna for
hi-fi results.



The rooftop antenna system installed where I am living now works well
for
all the TV channels - but has no FM band signals available. They
appears
to have been removed by a filter.


Well then install a better antenna of your own.


** Small problem with the body corporate.

Plus you have missed the point of the example - as ****ing usual.





With only a small frame aerial sitting on the floor next to it the
AM100
works well in my lounge room.

Its still not as good as a decent FM signal.


** Good AM is still there when decent FM signals are not to be had.



And the neworking of AM signals around the country mean
that the signal has gone through much electronics on its way around
prior to being transmitted.


** Same problem with FM.

The ABC FM signal in Sydney used to be poor to putrid when it originated
in Adelaide.

On those times an Opera House concert was fed in in Sydney the improvement
was massive.



And on a decent AM tuner with at least 10 kHz of AF bandwidth,
and excellent dynamic range ability, the deficiencies of
the transmitted signal from many AM stations is all too obvious.


** The deficiencies of FM are just as bad due to overprocessing and MP3
type storage methods, given that a very high audio standard is quite
possible.




........... Phil

Henry007 wrote:

Whatever happened to AM stereo anyway?

Well, here in Detroit (right on the Canadian border), we have at least
one AM stereo music oriented station which broadcasts with excellent
fidelity. It's CFCO 630 kHz from Chatham, Ontario. Other AM stereo
stations in the Detroit area are WJR (760 kHz) which has an excellent
music program on early Sunday mornings and a religious station on 900
kHz.

I have several AM stereo capable receivers (the Carver TX-11b tuner,
the Denon 680NAB tuner, an Aiwa pocket radio from Japan, and the very
first AM stereo radio model SRF-100 from Sony), but none beats out the
superb AM receiver on my 2003 Ford "Premium" audio system (the one
with the 6 CD changer built into the dash). When tuned to CFCO,
listeners are convinced they're listening to a good quality FM stereo
signal.

If you have a chance, try to listen to a Ford "Premium" receiver's AM
section. The 2001 through 2003 models are the best. The AM fidelity,
even on mono stations, is utterly superb.

In 2004, some idiot engineer at Ford decided to "enhance" the AM
section by narrowing the bandwidth (and therefore fidelity) when
receiving a weak station. Thus, the superior fidelity and stereo is
only present on very strong stations. On weaker stations, the radio
sounds as bad as every other radio on the market.

This Ford "Premium" radio shows just how great AM can sound if the
radio is designed correctly. It's a shame that AM is simply an
afterthought in most car and home tuners these days.

"Phil Allison" said:

** AM has several advantages technically over FM. The signal is not
prone to nasty multipath distortion, travels through brick walls with little
attenuation, does not need a high mounted directional antenna to avoid
constant signal drop outs and hence more distortion.

Umm.......isn't that more a function of frequency instead of
modulation?
Boy, I need to get out them old text books more!

--
Sander deWaal
Vacuum Audio Consultancy

Sander deWaal wrote:

"Phil Allison" said:

** AM has several advantages technically over FM. The signal is not
prone to nasty multipath distortion, travels through brick walls with little
attenuation, does not need a high mounted directional antenna to avoid
constant signal drop outs and hence more distortion.

Umm.......isn't that more a function of frequency instead of
modulation?

Er yes, and signals of 100 MHhz reflect and cancel more than
those at 1 MHz.
But FM sets depend on enough signal to make their
IF stages act in a permanent state of gross overload, so
there is no amplitude amplification, so a large variation of signal
amplitude has no effect on the sound, until the signal
drops below the "limiting threshold", and the signal easily
dissappears suddenly.
The AM set has to preserve the amplitude variations, and a careful
control of gain via an AVC circuit means the final IF amp stage
is made to work in the best bias position, and large variations
of signal strength has little effect.


Boy, I need to get out them old text books more!

Indeed.

Patrick Turner.



--
Sander deWaal
Vacuum Audio Consultancy

"Sander deWaal" wrote in message
...
"Phil Allison" said:

** AM has several advantages technically over FM. The signal is not
prone to nasty multipath distortion, travels through brick walls with
little
attenuation, does not need a high mounted directional antenna to avoid
constant signal drop outs and hence more distortion.

Umm.......isn't that more a function of frequency instead of
modulation?


** AM refers here to the AM band.

The frequency range is well known.




.......... Phil