"Jon Noring" wrote in message
...

snip (here and other places)

Another way to look at this is by a volumetric analysis, since one can
take advantage of plugging modules in a motherboard-like fashion.
Let's assume the modules will be 70 mm by 40 mm, and let's assume we
have to space the modules 19 mm apart because of the height of the
components soldered on. (Is this reasonable? -- 19 mm is the spacing
between PCI boards on a PC MB.) This means each module must minimally
take up a volume of 53,200 mm^3. 120 modules therefore will occupy a
minimum of 6,384,000 mm^3 (6.4 liters). This works out to a cubic box
186 mm on a side, or in English units 7.3" on a side (alternatively,
it works out to about 390 cubic inches for those not used to working
in metric.)


Don't forget you will have to swich those modules in an out of circuit. The
switch and all the associated wiring will significantly add to the space.

The wiring for the switch will also probably affect the tuning of the
modules forcing them to be tuning 'in place'.




Of course, a cube is aesthetically and practically not the way the
modules would be distributed. So let's assume we plug the modules into
the "motherboard", with the long side (70 mm) sticking up. This would
yield a single motherboard footprint of 142 square inches, or about
one foot on a side, and about 3" tall. If we split it into two
motherboards, each holding 60 modules, then the footprint would be
8.4" on a side, with a height of about 6".


If the long end sticks up, you have the inout and output of the modules on
the same end. This could result in unwanted coupling.

Yes, this is not an insignificant volume, but it is not a huge volume.
I notice that the three gang tuning air capacitor on my Philco 37-670
occupies a space of 3"x4"x7", or about 84 cubic inches, about 1/5 the
volume of the 120 module "box" (in a channel TRF, the tuning capacitor
would not be used.) Also remove the small volume taken up by the IF
section (no idea how much volume that typically takes up in a tube
set, but it is not tiny.)


snip


But for a tuner intended to tune in local stations, the channel TRF
tube tuner appears to have some things in its favor. As a
tube-o-phile myself, one can make several strong arguments in favor of
the channel TRF tube tuner: 1) the circuitry is "clean", no IM mixing,

Conceptually it may appear clean, but the proposed switiching of many
modules adds a new complexity. All the wiring associated with a swicth will
cause more problems that the design solves.

2) the bandpass filters are *perfectly* optimized for each channel --
no compromises (this is a *huge* attraction),

If you are looking for broad band with reasonable attenuation of other
stations, a superhet is much better as there is only one signal you are
optimizing for.

3) provides the ability
to plugin different bandpass filters for a particular station (if
needed), and 4) *may* be more amenable to a kit than would a full-
blown superhet design.

I would think that a kit should be simple, the proposed solution is not.



First, I assume that sensitivity is largely a matter of the RF amp
itself (and number of RF amp stages), not the bandpass filter itself
(although the filter should not overly get in the way of RF amp gain.)
But if the bandpass filter plays a greater role in sensitivity than I
realize, shouldn't an optimally tuned bandpass filter in the channel
TRF concept significantly outperform the limited and sub-optimal
single or double stage bandpass filters one is *forced* to use for
continuous tuning?

If you are only looking at a single aspect of the design (get all unwanted
signals out at the earliest point in the radio) then you may be correct. But
if you look at the overall design, then you will see there are tradeoffs
that must be considered. If the front end can tolerate the unwanted signals,
then IF filtering can deal with them and you have a workable solution that
does not have the alignment problems you would look at with a TRF design.


Second, each tuning module (for a single frequency) is, by and large,
independent of all the other modules. Thus, this simplifies the design
process since one doesn't have to share the same bandpass component
values from channel to channel, except maybe the RF transformers. This
should make it much easier, not harder, to achieve the performance
goals.

snip

(I keep looking at advanced radio circuits and see such a spiderweb of
wiring between the various stages, wondering why the hell it is all
there -- I wonder how much of that complexity is due to not being able
to properly optimize the RF bandpass filters for a given frequency,
thus requiring all sorts of work-arounds to get good overall
peformance.)


I think you really need to understand that spiderweb before making that kind
of statement.


snip


Almost the entire amount of AM radio reception theory that has ever
filled the minds of conscious humans has been repeatedly explained
so far in this thread, so you have all the knowhow you ever wanted,
so what's the hold up? Stop dithering, and go to it man!

Actually the know-how has not been explained in full! :^)


And that know-how does not all need to be explained here. There are plenty
of resources on the internet, look for them and study them.


Thanks for your feedback. It is definitely adding useful information
to this thread.

Jon Noring


IMO this thread and the related theads are more on-topic for rrs than much
of the stuff posted by one of the people considering this to be off topic.

craigm