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It is a direct conversion receiver but I changed LM386 to 2N3904. The X on a .01uf capacitor means it is totally removed. The tuned inductor is DIY7 series with built-in capacitor. I built 7.050 MHz version so I used DIY7-7. You can also use toroid coils of course. The major part of this design is the 2N3904 audio amplifier. It is biased by NE602 and it is driving a low impedance headphone. Also, it is very rare to switch power like that, but my result seems to be very positive.
Some questions about your circuit. First I see no information
about the tuned inductor. What did you use? Second, you have an
X through a .01uf capacitor on the collector/output of the
transistor. Does that mean that collector goes directly to
ground? Or does it mean the entire connection including ground is
removed? In looking at it, it looks a lot like most of the direct
conversion receivers I have seen, with the exception of the
transistor rather than an LM386 audio amp. Chuck Adams did a
group project of a direct conversion receiver and provided gerbers
for buying your own pc boards on his email group (qrp-tech). He
used a toroid for that input coil. Granted, it also uses an
LM386 audio amp so might not be as friendly to a 3.5 volt battery
but works well on a 9 volt battery.
Thank you for the idea.
On 10/14/2018 7:49 AM, Adam Rong wrote:
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
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.