Saturday, January 23, 2010

I'm making a transistor radio from scratch using only 2N4124's

I have a box full of 2N4124's. I also have a box of RCA IF
transformers of various Q's. So i have decided to make a transistor
radio from scratch using parts from my scrap parts collection.

Today i built a 2 stage IF amplifier, where, each stage provided
about 30 dB of gain. Circuit Q was very high, set by the IF
transformers which coupled each stage together.

I built a full-wave envelope detector using one of the IF
transformers and two germanium diodes.

I injected a tone into the base of the first stage and sucessfuly
used it as a mixer.

I successfully tuned in AM broadcast bands by injecting an LO into
this mixer, listening to local sports and talk stations.

Next steps:
1. need to build a VFO that can swing a couple of volts on the output.
2. modify the IF amps so that they are adjustable gain
3. build a front-end that is band-limited with a bandpass filter or
adjustable resonator transformer of some kind.
4. look into using this at short-wave frequencies, might have to
build an RF amp and pre-selector.