On Fri, 19 Nov 2010 07:43:35 -0600, joe wrote:

Which components did you determine to be 'extra' and why?

Hi Joe,

To enumerate:
Ra, 50 Ohms
Ca, 40pF
R1, 308 KOhms
D1, a selection criteria of 200nA Ir
Co, 200pF
and
Ro, 154 KOhms

The question why? you apply to me is as easily asked of the author
because he says nothing on their choice, which give every appearance
of being capricious.

Let's look at the last first, in the audio output we have a high
frequency cutoff knee of 32 KHz, why? I can think of nothing to
justify that selection that is 10 times outside of the passband.

We have an audio load of 154 KOhms, why? I can well imagine this
being a piezo headset, but is it an optimal load (it would appear that
the diode needs a heavier current draw than that). It is not a
standard resistor value, so there must be some motivation for this
value - but that is left to our imagination.

D1, a selection criteria of 200nA Ir, why? Is this a good selection,
or a bad one? Again, lacking the information of motivation....

R1 appears to be inserted on the basis of an anticipated Q, a topic
that is wholly absent from the computations and discussion! Why? This
is the component I thought of as being "extra."

Ca and Ra have already been decried, and the Ca placement looks
suspiciously on the wrong side of Ra.

So, what values would you suggest?

I cannot imagine trying to figure out the agenda for the author. The
piece is wholly unmotivated beyond being an etude of computation.

The values for Ra and XCa are infinite in possibilities. For the
average BCBer with limited antenna options, Ra would typically be low,
maybe an Ohm at the very highest (and probably much less). XCa would
be high, maybe a KOhm (but not suspiciously high like the current 7
KOhms). As you can see, the differences from the original are
considerable.

You talk like the pdf had significant faults, but your reply is so vague
that you don't really add anything. Please share you understanding so that
others may learn.

Please reread my comments for praise where praise was due. If the
rest sounded vague, it was entirely due to the vague material offered.
Consider that also.

Further, asking me why don't I do ______ (fill in the blank), I have
no interest in pushing that rock up the hill - but thanx for asking.

I am far more interested in the detector side of this, but the Xtal
radio brotherhood approach this like Penitentes continuously flogging
themselves in order to attain a religious high.

I would choose a quasi-digital solution with a shift ring register
commutation style of detection. But that means I need a battery
(ANATHEMA!!! I hear the cowled acolytes sputtering). If I use a
battery I could as easily, sinfully listen to a transistor radio - and
my MP3 player already suits my needs with its built in radio function.

40 years ago I worked on BaseBand sets and designed with synchronous
detectors. This is all very interesting to me from my former
devotion, but this XTAL splinter is rather provincial.

73's
Richard Clark, KB7QHC