Patrick Turner wrote in message ...
Syl's Old Radioz wrote:

"Jon Noring" a écrit dans le message

...high-performance, tube-based AM (MW/BCB)

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers ...

Audiophile AM is an oxymoron...

Syl
Now there's talk of digital broadcast, and the phasing out of FM and AM
broadcasting.
But I don't expect it to dissappear soon, and even more channels for
people's attention seem
to spring up daily to consume the leisure time of the masses,
and TV gets the main share.
Digital recievers need to be costed below the existing radio receiver
costs before
folks will buy them as an add on for their TV watching.
People's expectations about home entertainment are far beyond
just sitting down listening to music.
Most AM is listened to in cars, if at all, but usually while folks are
doing something else.
There will always be broadcasting of some sort, because its possible,
and the spectrum exists, but the programme quality decline continues.
As fewer listeners tune in, there are less advertisers willing to pay
the stations,
and its not worthwhile building a super dooper radio to listen to them.

I have 3 HRO receivers in parts from which I plan to get two good ones,
I have several other radio projects to do, but alas no time, since I
have to work for
a living.

I'd like to try using a 2 MHz IF strip for my A radio, because at least
there
3 stations here worth listening to out of the total of 7.

I figure the 2 MHz IF frequency would allow
a Q of 50 for each LC circuit, and thus the BW would be 40 kHz for each,

so with 4 or 6 consecutive LC circuits the BW could be 20 kHz,
thus allowing 10 kHz of audio BW.
Perhaps single tuned IF coils are all that's needed.
The single tuned high Q IF auto tranny is pretty awful at 455 kHz, as
used in transistor
based circuits because with a Q of 100, the BW is only 4.55 kHz,
and with two such coils you have only say 3.6 kHz, so only 1.8 kHz of
audio can
pass, and many transistor radios have only 1.8 kHz of audio BW.
Some tube types only have that much. I have measured plenty
of impressive looking tube sets with RF stages, and the total number of
tuned circuits is
about 6 including 4 IF coils, and the bandwidth narrows down badly.

Communications radios sometimes used lower IF at say 100 kHz
to take advantage of the lower bandwidth for a given Q.
This allowed very good selectivity for short wave,
but was hopeless for local station AM.

Its possible that by removing many turns off existing 455 kHz IFTs,
the 2MHz could be achieved.

The oscilator would operate at the BCB frequencies + 2 MHZ.
So the oscillator coils and circuit would need revision, but then that'd
be easy,
since the coils do not differ much from the usual low end short wave
types.

The other way of doing an AM radio today is to use totally digital
techniques for converting what is coming from the antenna and pull out
the audio from
any wanted station in ways which nobody in 1935 could ever have
imagined.
I think this would be an interesting digital project for someone.

Everyone has a PC at home these days, and it sould be easy to
use it to sift out a few radio waves.

But if fidelity isn't transmitted, not even a PC can decide correctly
what to substitute for missing audio HF.


Just my 3c worth,

Patrick Turner.

I don't have 3c and I only have 2GB. WTF do I want to do that on this
POS. Why does 'radio' have to be done on a computer? Get moving and
build a dedicated device (radio) instead of using a damned computer.
This should be in a sci. group.