Darren's Crystal Radio and Amplifier
Found your visitors section, thought I'd take a few quick photos of my #1 attempt. This project started as a group activity, run by our church, called 'The Shed' where us guys get together and build things.
The coils are wound on 1 inch plastic tube. I used 0.5mm wire as I found this easier to wind than the 0.3mm. TIP: make sure you recalculate turns required, this was my first lesson learnt.
You'll notice the coils are mounted on the same nice looking clear plastic tube. Unfortunately this creates a coupling between them as they're on the same plane. TIP: To greatly reduce coupling, mount the coils at right angles to each other.
Full Wave Diode Configuration
I did some internet research and experimented with different diode configurations.
1 diode works ok.
2 diodes didn't improve much for me on this crystal radio, maybe my #2 attempt.
4 diodes in full wave bridge proved to give the loudest output so I've stuck with this.
Amplifier with selectable input impedance
My amp module has an audio transformer with 2.5k 5k 10k and 20k inputs. (first 4 switches) With the audio transformer I found depending on the station your tuned into the taps give different tones. The 8ohm output is connected to an amplifier kit available from Jaycar Electronics for under $6. By default the amp has a gain of 41 with the option to short the 1k resistor for 200X gain. (5th switch)
How does it work?
I managed 5 local radio stations here in Sydney. The closer louder stations drowned out and mixed with the less powerful ones. Being my #1 crystal radio I found this very exciting and having learnt a few things started planning #2 radio. Please e-mail me with your comments.
A very neat job, Darren. I sure like the shine of the wood bases. – Dave