Just a thought but I recently found out that many of these SDR’s do not fully implement the circuitry required for direct sampling mode.
It is not supposed to be that difficult to get working but if you are making boards might as well put it into the design.
I thought about this during the design, and absolutely would have included some connector, even just as test points, for the unused i input… if I had the space. After a full redesign (rearranging the tuner, rtl2832u, using a smaller eeprom, etc.) I expect it would be possible, but I’m happy with it currently since I can pull out my SDRPlay if I want to go below 24mhz. The connections are already marked in the schematic if anyone wants to add them to their own design though.
Some models add some extra components (filters, a balun, etc.) to allow the same connector to be used for both the tuner and direct sampling. Adding that would be even more difficult, maybe impossible without putting components on the back, but could be possible. I have no plans to add that to this card.
Hello,
Thanks for the amazing design. I’m actually looking to build one of those myself, and then eventually relayout the card for a different form factor. I do have some questions though.
Besides the RTL and tuner chip, does your design require anything else from the original RTL-SDR dongle? Can I salvage everything(RTL chip, R820t2, TCXO) from one of these cheapo dongles? If not, where else can I score an equivalent TCXO?
Does your design work as is? When sourcing SMD passives, do I need to make any special considerations? You schematic has the inductor value as still being “?”, what value ended up working?
Did you make any progress on impedance matching the antenna?
When doing layout, did you make any special considerations there? Did you impedance/length match any of the traces? Also would you be willing to review my layout when I finish it?
Thank you again for such as great design.
I did build one a while back (@Kyle_Reis posted my photo, thank you). I took another crack at it using a 3D printed expansion card.
I bought the following items:
I removed the circuit board from the SDR housing. I had to sand down the LED on the bottom side (not visible) to allow the circuit board to sit low enough in the 3D-printed housing. I attached the USB adapter and used Gorilla Glue to secure everything. Once the glue dried I was able to slide the SDR in and everything worked great.
The circuit board does stick out slightly, but it’s streamlined enough for my purposes.
How is the USB-A connector attached to the board? You might be able to remove it, and solder a USB-C adapter on further back so that it comes out flush with the edge of the expansion bay.
