Here I show you my recent project.
Inspired by the receiver portion of VK3YE’s tiny toy CW transceiver (search YouTube videos to know more about this radio), I wanted to build a small receiver with minimal amount of parts but still give good result. Also, I tried to build the radio with a battery pack, so I can take it everywhere and plug in headphones and antenna, even without switching the power, i can immediately receive. And here is the result: a radio with only 12 parts including the battery pack. I powered it by one cell of Li-Po battery and the voltage (3.6-4.2V) is lower than the spec’ed lowest voltage of NE602 (4.5V) and it will give a bit lower conversion gain but it is good here as it rejects BCI even better. I didn’t choose an audio connector with a switch so I wired the power line of NE602 after the headphone, and I need to add 1uF to NE602 to avoid self-oscillation. The sensitivity is not high but it give good enough volume to a sensitive stereo headphone of 32 ohms in series if you have a standard size end feed or dipole antenna. And the noise pattern is quite good to hear.
The overall current draw is about 3mA so with a small battery pack of 3.7V 600mAh, I can hear about 200 hours! If you have all the parts on hand, please build and let me know your result. If you use Choc perf board to build this radio like me, I will really appreciate it.