AM Radio Circuit Design

[Franklin]

I'm quite new to Electronics, and have been working on understanding
an AM radio circuit. I think I've gotten most of it, but I'm stuck at
a few points.

The schematic can be seen at
http://support.radioshack.com/support_games/doc60/60245.htm , or, for
a better picture, at
http://support.radioshack.com/support_games/doc64/64800.pdf .

Here are my questions:

A) Block (1) - I recognize the tuned circuit, but its not in any
configuration that I'm familiar with. Normally, I've seen the signal
come in, and a tuned circuit bypass to ground, and then signal out.
Here, I don't see any signal in (where does the antenna connect to?)
or signal out - only to ground. How is this working?


B) Why is an inductor used to couple to Q1?

C) There are several capacitors which bypass to ground along the way -
from right to left, a 0.1uF, a 0.01uF, another 0.01uF, and a 0.05uF.
Are these all used to detect the AM - that is, to let the HF drop to
ground while the audio carries through? Why do you need so many?

D) Block (4) - How can you couple with only a 0.022uF capacitor -
won't this block all but the lowest frequencies?

Can anyone help me with any of these questions?

 

[Luhan Monat]

A) Block (1) - I recognize the tuned circuit, but its not in any
configuration that I'm familiar with. Normally, I've seen the signal
come in, and a tuned circuit bypass to ground, and then signal out.
Here, I don't see any signal in (where does the antenna connect to?)
or signal out - only to ground. How is this working?

AM radios use a coil on a large ferrite rod as the antenna.

B) Why is an inductor used to couple to Q1?

The extra winding is to match the lower impedence of Q1.

C) There are several capacitors which bypass to ground along the way -
from right to left, a 0.1uF, a 0.01uF, another 0.01uF, and a 0.05uF.
Are these all used to detect the AM - that is, to let the HF drop to
ground while the audio carries through? Why do you need so many?

They help keep residual RF from getting to the audio stage.

D) Block (4) - How can you couple with only a 0.022uF capacitor -
won't this block all but the lowest frequencies?

No, its in series, it passes all but the lowest frequencies. This helps
the radio play louder by keeping low frequencies from saturating the
audio output.