I want to know which LPF design tools you used? What type of  filter you set? could you please update its settings and screenshot to you Github?

Sure, I have added the details here: https://github.com/dawsonjon/PicoRX/wiki/Hardware-Design#low-pass-filters

Think your very much. I found  maybe a small mistake on the page 4 of you schematic (pipicorx.pdf), The LPF of IQ signal cutoff frequency should be 60kHz not 59Mhz?

Nice work! But I have a question, The project use only a ADC for IQ sample so the I and Q channel are not synchronous, Q channel will be a small delay. My question is it is necessary to do IQ correction? 

https://github.com/df8oe/UHSDR/wiki/IQ---correction-and-mirror-frequencies

how is the final mirror rejection ?

Hi, that's a really good question!

In this design the ADC is used in round robin mode and samples the I and Q channel alternately. The Q samples are actually mid-way between the I samples. It turns out that this is just as good as sampling I and Q simultaneously at half the rate.

However, there will still be differences in the magnitude and phase of the I and Q channels due to component inaccuracies etc, and this causes images to appear.

I haven't implemented IQ imbalance correction yet, but it is a feature I would like to implement at some point and I think it would improve the image rejection performance. Even without correction, the images are significantly attenuated,  although I don't have an accurate image rejection measurement.

https://www.youtube.com/watch?v=HWZr2OXQ3vs&ab_channel=RadioLogUD3SBV

Cool! That's a very neat PCB you have put together. Nice job!

Sorry I have very limited understanding on rpi, sdr, and antennas in general but would it be possible to receive signals up to 40ghz with this? Or even detect them somehow. Thank you, very exciting project you have!

Hi, thanks very much for your comment. Some people have had success recieving VHF and UHF signals by using an external down converter. I suppose in theory it might be possible to extend the frequency range to 40GHz with suitable downconversion, but to be honest I think it sounds very ambitious, and this project probably wouldn't be the best starting point.

Thank you! I have already figured it out and corrected the controls and menu interface. The printed circuit boards of my design will arrive soon.

How to compile your code? I only worked with Arduino IDE. What is needed to compile your code?

Hi, You basically need to install the Pi Pico C/C++ SDK The official instructions are here: https://www.raspberrypi.com/documentation/microcontrollers/c_sdk.html

Once you have this you can then build the firmware using cmake. I have added some build instructions here: https://github.com/dawsonjon/PicoRX/blob/master/BUILD.rst.

If anything isn't clear, give me a shout :-)

Best of Luck

Jon

 you are NOT IQ sampling,so why use the tayloe mixer? rpi pico has only one ADC , you cant IQ sample with a multiplexed ADC,interpolating doesnt help either, remove all that un necessary circuitry and directly sample the signal. if you need more bandwidth overclock the ADC, I heard it goes good upto around 3Ms/s, better would be using a bluepill altogether which comes with two ADC's

Hi, that's a very interesting question, I'm glad you asked :-)

There is a neat mathematical trick! Although the ADC can't sample I and Q at the same time, you can sample them alternately. If you replace the "missing" samples with zeros, the information in the missing samples relates only to the outer half of the spectrum.  The central -FS/4 to +FS/4 still contains useful data, the outer half of the spectrum contains no extra information it is simply a reflection of the inner half,  and gets filtered out. I did a short write-up on the technique here: https://github.com/dawsonjon/PicoRX/wiki#sampling-iq-data-using-a-round-robin-adc.

So... with a 500kS/s sampling rate (sampling I and Q alternately)  you get 250kHz of useful bandwidth (rather than the 500kHz you would get if you could sample I and Q) at the same time, conveniently 250kHz is just enough to span the frequency gaps in the PIO based oscillator. 

I like your direct sampling suggestion, in fact this project made an SDR this way https://hackaday.com/2021/03/16/the-raspberry-pi-pico-as-an-sdr-receiver/, as you say the bandwidth is a limitation of the linked example which only works up to 250kHz but it does have some uses nevertheless. Elektor used a direct sampling SDR to receive MSF radio clock signals https://www.elektormagazine.com/magazine/elektor-260/60555. A 3MS/s sample rate would get you up to 1.5MHz which would allow you to receive some MW stations.

To listen to SW stations you really need some kind of mixer. The Tayloe mixer is fairly  simple and extends the frequency range of the receiver to 30MHz giving coverage of the LW, MW and SW bands, One collaborator has even managed to extend the frequency range of the Pi Pico Rx into the VHF band using a second oscillator and mixer.

Of course there are alternatives to IQ sampling, we can use a single mixer and real-only ADC sampling, but you would need some other method to remove images, probably involving additional mixers and filters, so don't think this would result in a simplification overall.

The blue-pill looks kind of neat too, I'm sure it would make an excellent basis for an SDR receiver, and being able to sample both I and Q simultaneously would double the bandwidth.

A very interesting project! I would like to change the menu navigation algorithm and the size of the inscriptions in the menu! I will make a miniature receiver with an SDR Tayloe-based circuit. Will there be a firmware update?

Thanks very much for your comment. Best of luck with your project, I would be interested to hear how you get on. I haven't got any plans to update the firmware at the moment, but I am still maintaining it and will address any issues raised and publish any firmware updates.

What ICs are you using? I'm thinking of building a similar thing or working off your design and code to make a Pico-based SDR for the HF bands. Any schematics, design files, and code would be much appreciated even if not complete or fully documented.

Hi, Thanks for your interest! I'm using a FST3253 for the mixer, and LTC6227 for the dual op-amp, but I used an LT6231 in the prototype and that worked fine. The PCB uses 74CBT3251 for the low-pass filter switching and a LTC6226 as an *optional* pre-amplifier. I have just uploaded the Schematic, Bill of Materials, and Gerbers.  The code (and loads more documentation) is on the github project https://github.com/dawsonjon/PicoRX and the wiki https://github.com/dawsonjon/PicoRX/wiki.  If anything is missing, or needs further explanation, please let me know. Thanks Jon

I've been looking at your schematics and I'm thinking of basing my design off your hardware and code (adding transmit using the unused half of the multiplexer and adding lithium battery support), but I have a question: Why do you have a switchable bandpass filter array? I've never seen that on any other Tayloe-based radios (the (tr)uSDX just pipes the RF input directly to the Tayloe detector for example). EDIT: realized that the bandpass filters are necessary to prevent image frequency interference.

Hi, 

I like your idea of using the Tayloe mixer for tx, it's a very elegant solution and it even gives you a tx/Rx switch. One thing to keep in mind is that the NCO in it's current form only has a resolution of 100kHz or so. This would mean that the tx IQ signals would also need a similarly high bandwidth. It would be difficult to achieve this with a PWM without compromising resolution and ripple. A better option would be to improve the resolution NCO by applying some periodic frequency correction, a resolution of less than 1Hz should be possible, but would probably consume more CPU. Definitely doable though.

It sounds like you have already figured this out, but the Tayloe detector mixes the RF using a square wave. This means that it receives odd multiples of the tuned frequency at a reduced level. The switchable filters help to remove this.  It works without the filters, but you tend to get interference from stations in other bands. A low pass filter should work, but a band-pass filter can also help to reduce interference from high power broadcast AM stations.

I think most Tayloe based radios have some form of filtering on the input. Soft rock, mchf, elecraft kx2 for example use switchable band-pass filters in the receive path. I think that the (tr)uSDX is using the resonators in the TX section to also provide band-pass filtering for the receiver.

If you were going to add transmit, it would make sense to reuse the Tx filters for Rx too, rather than doubling up.

Best of luck with your project.

I'll probably just use a reasonably priced fast dual DAC to generate the IQ signals for the reverse Tayloe. I'll also incorporate a Si5351 clock gen to generate a more accurate frequency signal (although it'll be optional since PIO-based freq gen works at least for Rx). (Hmm your idea to add periodic frequency correction to provide more resolution to the PIO clock gen sounds interesting although idk how I would implement it). I'll definitely keep the bandpass filters since they'll be beneficial for Tx and they improve Rx performance. 

Thanks for the information and documentation on your project. It's really helpful having something to base my version on.