Re: Tiny Toy Receiver

Adam Rong


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.


在 2018年10月15日,上午2:15,Jim Pruitt <jpruitt67@...> 写道:

Hello Adam.

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.

Jim Pruitt

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 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.



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