# A Question About The Legendary Confuser, The Radio

Discussion in 'Electronic Basics' started by Pete Holland Jr., Apr 12, 2006.

1. ### Pete Holland Jr.Guest

Hey, everybody!

I got busy and had to take a break from playing with electronics, but I'm
caught up and looking to continue the learning process. A thought struck
me today while examining a radio circuit, and I wanted to see if I'm on the
right track.

To show the page of music I'm on: a while ago, I posted a question asking
where the ground on a transistor radio was because a ground was necessary
and I couldn't figure out how they did it. I was informed it was part of
the antenna. The kit has you start by building a crystal radio first, then
a transistor radio. It says a transistor can amplify. So far, so good.

While examining the circuitry and the schematic, a thought hit me. As I
traced the flow of the current, it appeared that the battery current flowed
along the transistor, but not into the antenna coil. It looks to me like
the transistor radio is actually two more or less independent circuits, and
the transistors act as a bridge. The first circuit is a crystal radio.
Where it joins the transistors, the signal amplifies and gets boosted by
the battery, and that's the second circuit that enables you to hear it,
control the volume, etc.

Am I right about the two circuits working together, or am I missing
something?

Dobre utka,
Pete Holland Jr.

Pete Holland Jr., Apr 12, 2006

2. ### John PopelishGuest

Pete Holland Jr. wrote:
> Hey, everybody!
>
> I got busy and had to take a break from playing with electronics, but I'm
> caught up and looking to continue the learning process. A thought struck
> me today while examining a radio circuit, and I wanted to see if I'm on the
> right track.
>
> To show the page of music I'm on: a while ago, I posted a question asking
> where the ground on a transistor radio was because a ground was necessary
> and I couldn't figure out how they did it. I was informed it was part of
> the antenna. The kit has you start by building a crystal radio first, then
> a transistor radio. It says a transistor can amplify. So far, so good.
>
> While examining the circuitry and the schematic, a thought hit me. As I
> traced the flow of the current, it appeared that the battery current flowed
> along the transistor, but not into the antenna coil. It looks to me like
> the transistor radio is actually two more or less independent circuits, and
> the transistors act as a bridge. The first circuit is a crystal radio.
> Where it joins the transistors, the signal amplifies and gets boosted by
> the battery, and that's the second circuit that enables you to hear it,
> control the volume, etc.
>
> Am I right about the two circuits working together, or am I missing
> something?

This is certainly a valid way to break this system down into
functional blocks.

John Popelish, Apr 12, 2006

3. ### Tom BiasiGuest

"Pete Holland Jr." <> wrote in message
news:e1hqlu\$229\$...
> Hey, everybody!
>
> I got busy and had to take a break from playing with electronics, but I'm
> caught up and looking to continue the learning process. A thought struck
> me today while examining a radio circuit, and I wanted to see if I'm on
> the
> right track.
>
> To show the page of music I'm on: a while ago, I posted a question asking
> where the ground on a transistor radio was because a ground was necessary
> and I couldn't figure out how they did it. I was informed it was part of
> the antenna. The kit has you start by building a crystal radio first,
> then
> a transistor radio. It says a transistor can amplify. So far, so good.
>
> While examining the circuitry and the schematic, a thought hit me. As I
> traced the flow of the current, it appeared that the battery current
> flowed
> along the transistor, but not into the antenna coil. It looks to me like
> the transistor radio is actually two more or less independent circuits,
> and
> the transistors act as a bridge. The first circuit is a crystal radio.
> Where it joins the transistors, the signal amplifies and gets boosted by
> the battery, and that's the second circuit that enables you to hear it,
> control the volume, etc.
>
> Am I right about the two circuits working together, or am I missing
> something?
>
> Dobre utka,
> Pete Holland Jr.

For a simple tuned circuit you can surely look at it that way.
Tom

Tom Biasi, Apr 12, 2006
4. ### Walter HarleyGuest

"Pete Holland Jr." <> wrote in message
news:e1hqlu\$229\$...
> [...]
> While examining the circuitry and the schematic, a thought hit me. As I
> traced the flow of the current, it appeared that the battery current
> flowed
> along the transistor, but not into the antenna coil. It looks to me like
> the transistor radio is actually two more or less independent circuits,
> and
> the transistors act as a bridge. The first circuit is a crystal radio.
> Where it joins the transistors, the signal amplifies and gets boosted by
> the battery, and that's the second circuit that enables you to hear it,
> control the volume, etc.

You can think of a transistor as a device where a small current flowing
through one part of it (specifically, the base-emitter junction) controls a
larger current through a different part of it (the collector-emitter
junction). So, that does tend to mean that the transistor acts as a bridge
between separate parts of the circuit, although it doesn't have to always be
that way.

In your case, the signal from the antenna is creating a small current that
flows through the BE junction; that controls a larger current (whose power
source is the battery) that flows through the CE junction and also through
the speaker or earphone.

Note that a transistor does not create power (or current or voltage), all it
does is control it. It's like a valve.

Walter Harley, Apr 12, 2006