Hello,
Over the past few weeks I’ve been working on an RTL SDR expansion card.
The plan is to post updates here.
I previously posted about this project here, after reverse engineering the RTL SDR schematic and getting most of the way done with designing a board.
Since I can’t find the chips online, the plan is to take the rtl2832u and r820t2 chips out of a cheap RTL SDR, which unfortunately raises the barrier to entry by quite a bit.
For that reason, among others, I don’t plan on selling these (at least not at a reasonable price or in large quantities) unless I get access to the chips. Either way, I’ll release the design so those crazy enough to desolder QFN chips can make one.
Since that first post, I finished and ordered a version of the board for testing:
You’ve probably already seen this, but @John_Mayson shared that the internals of a Nooelec NESDR Nano 3 (which uses the same rtl2832u and r820t2 chips) already fit mostly inside of the USB-A expansion card without any soldering required.
It does stick out a little bit, although if you removed the USB-A connector from the SDR and soldered a USB-C connector in its place (instead of just using a small adapter) it would probably fit fully within an expansion card (it might fit within a headphone expansion card, the hole looks to be roughly the correct size). That would still be simpler than what you’re doing.
I saw that in the SDR idea thread, but it didn’t have photos and I couldn’t find it on archive.org, so this is the first time seeing just how much smaller the NESDR nano 3 is compared to the card. Knowing that a NESDR Nano 3 can fit within the card slot actually inspired me to go ahead with this project.
That would still be simpler than what you’re doing.
That is true, but I’m more doing this because I find it fun, and because I get to learn about designing PCBs. I also prefer an SMA connector since it gives me more flexibility with antennas.
Another thing to point out here is that I’m only putting components on one side of the board. The Nano needs to cram things in on both sides, and it looks like it uses a linear regulator for the 1.2v rail which would generate more heat.
This is more of a minor update, but there won’t be much else to say until the PCBs arrive.
For the case, the SMA connector is the only thing I need to modify the example case for. I’m not quite sure how that connector will fit physically, so I’m just getting the example case printed for now.
I desoldered the chips a few days ago, and managed to clean up the board a bit too:
I’m somewhat worried that I damaged the chips with the amount of heat applied, but I do have a few extra SDRs ready for sacrifice if anything goes wrong.
Here’s the back for reference, already flipped and aligned with the front:
Considering it’ll already have a connector on it, why not have the SMA on a small jumper wire? Alternately, you could look at using an SMC connector or a smaller one.
When I get my Framework 16 I plan to do a similar mod to what I linked (since I don’t have much experience with soldering) and 3D print an enclosure with room to contain the SDR with an SMA adapter connected. It’ll stick out byt most of the time I probably won’t have it in my laptop so that won’t be a big deal.
I really should have chosen faster shipping. Anyways, the other parts have been here for a while, so I have everything I need to start soldering it together tomorrow.
Yesterday, I soldered the QFN chips and the oscillator with hot air, then that evening I got the rest with my soldering iron. The QFN chips were a lot easier to do that I expected. The USB connector was the hardest part, especially with a soldering iron.
After checking for shorts, I plugged the board into a USB hub (plugged into my dock) so that if something went wrong, the hub would be damaged instead of my laptop. Surprisingly, it just worked! No issues so far. It does get very warm at times, but the board isn’t ever too hot to touch, even after letting it run for a while in the laptop without direct airflow.
This morning, I removed some material from the case to fit the SMA connector, which can be seen above. The top of the connector overlaps with the laptop slightly, but it doesn’t prevent the card from being fully inserted.
This doesn’t have shielding around the board, and putting it into a computer causes some amount of interference. But the goal of this project was to create a RTL SDR that fits in my laptop and works reasonably well, and I’m very happy with the result.
Next steps:
Design and print a better case
Release the design (which I want to clean up a bit first)
Work on impedance matching the antenna input properly, if I can get access to the necessary equipment. It works fine as-is, but the performance could probably be improved.
Assemble a second one (because why not, I have the parts to make four)
Are there components on the back? I didn’t notice any pics in the thread of the backside. You could use hot plate reflow for all parts that are on the top only.
There aren’t any parts on the back, so yeah that would probably be better, but I don’t really have the equipment for that. I’ll ask around, but for the second one I’ll probably just finish it with the iron (I did the hot air section of it earlier today).
I still don’t really have plans for significant production. I would consider doing small batches of a revised design given enough interest, but it would still involve soldering the main chips by hand.
Anyways, I do have extra parts… If you’re willing to pay like $100 for what is basically a $25-30 dongle, but in a form factor that fits in your laptop and with somewhat reduced performance due to the probable impedance mismatch, well, DM me and we can work something out. For the moment, I have an extra board already soldered together and enough parts for two more. If not, no worries. I’ll release the design either way.
PS: I’ve been relatively busy recently, so it’s been a while since I posted an update. If all goes well I should have more to say about the case soon.
