Yes, though Dr Volt did a great job I think. To really improve the receiver, I suspect one needs to add an RF bandpass filter and maybe a low-noise RF amplifier. But that would not be simple. Check out this channel I recently found. www.youtube.com/@M0NTVHomebrewing/videos

@@electronics.tinker Indeed. It's the difference between the most minimalist design that can be reasonably functional, and taking a particular design as far as it can go. The best possible RF amp, mixer, LO, filtering, and audio amp and processing can take a DC receiver pretty far.

Very interesting. What did you change to impedance match? Also, what analog multiplexer did you use? Most people use an fst3253 which has lower "on" resistance than the part I used. This affects the input impedance and size of capacitors. I paid little attention to this. I just experimented with the size of the caps. NA5Y uses a bandpass filter and, thus, more sophisticated matching. I wonder how much the arbitrary nature of the antenna wire slung over a tree affects this. NA5Y, being a HAM, might be using proper 50 Ohm antennas.

I found it to be a fun thing to do. I hope you do also. Check out Dr. Volt's video and NA5Y's channel also. There is a lot of material out there. Getting quisk working takes a little guess work. Let me know if you folks out there want more information on that. I have found quisk to work better than other SDR software I have tried with sound card based receivers.

Glad you liked it. I suggest also checking out w2aew's channel. He is an amateur radio operator (and his may be the single best electronics channel on youtube). Also see the NA5Y channel for more complete simple receivers, not necessarily relying on SDR.

I'm glad you found it interesting. I found that one of my computers has a soundcard that supports a 192k sampling rate (and without a filter to mess that up). I guess the quisk display essentially is a spectrum analyzer, but limited to a 192 KHz span centered on the LO frequency.

I used an MCP6002 without giving it much thought. I wanted the convenience of powering everything from 3.3V. I was just playing around with it and was surprised that it works as well as it does. Dan Tayloe suggests using a precision or instrumentation op amp but for a toy receiver like this, my bet is that other basic op amps can work. I think NA5Y used an lm324 in a tayloe detector. It's convenient to use a dual op amp. Dr. Volt used an amp that is especially good for driving sound cards. Just watch your power supply level, pay attention to biasing the antenna signal (like to 1/2 of the op amp's supply voltage). But also don't overdrive your sound card's input. If you have a scope, watch out for clipping. And use a long piece of wire for the antenna, ideally running outside. Cheers and good luck.

Which SDR radios do you mean? I agree that the quisk software requires guess work. Do you have any specific questions? The thing with SDR is that quite basic hardware (like an rtl-sdr v3) enables many things from listening to AM radio to receiving data from satellites. There is quite a bit of youtube content, but it takes experimenting for sure.

Done. See github.com/grughuhler/grug_lo_gen. Also, check out the videos and sites I mention in the description. Cheers.

Thank you very much. @@electronics.tinker

I don't have an atmega 328 so I am not sure. The task is to generate two 50% duty cycle square waves with one shifted in phase by 90 degrees from the other. You want the frequency to be 10-20 KHz different from the radio station you want to receive. The problem is that microcontroller timer hardware has limits to how it multiples and divides clocks to generate the final output frequency. I bet the atmega 328 can do it for *some* frequencies but maybe not for the frequency near the station you want to receive. This was the problem with the ADALM2000, actually. The Raspberry Pi Pico is unusually flexible in how it can multiply and divide clocks, but even it has problems. The way it divides can cause jitter. Many people who build simple radios like this (including Dr Volt and NA5Y) use an Si5351 chip to generate the quadrature clocks. This is a good idea. Si5351 modules you can use on a breadboard are cheap and available from Amazon. You would control the Si5351 from the Arduino using i2c-- but you really have to study the Si5351 to generate quadrature signals the best way. But many on youtube have done it so there are videos to study. I might do one more if I think I am adding something. I'll mention another option. You can generate a clock with 4x the frequency you need and then use a pair of flip-flops to convert that into the two quadrature signals that feed the mixer. There are also youtube videos on this. For example: kzfaq.info/get/bejne/hbJlZcle0JnNeXk.htmlsi=1-T5_9JH60DV_vtn. I see a good video on mixers on this channel also.

Thank you very much, I liked the flip flop version @@electronics.tinker

Well, in the interest of full disclosure, a good SDR receiver contains much more: low-noise amplifier with gain control, multiple HW band-pass filters and HW to select among them, analog to digital conversion is included (instead of using sound card), and it works at a far higher sampling rate, and USB interface. I think the SDR Play RSP1A is an example of a quite good but reasonably cheap SDR receiver. And the rtl-sdr V3 dongle is not as good, but you can do a lot with it for a very low price. Cheers.