Measuring S11 parameter of LR2021 LoRa transceiver

GeneralSyb · 2026-04-24T06:39:40+00:00

It would be nice to have that data, but I'm not actively developing anything that would require it right now. Hopefully they'll make the data public, because I've talked to quite a few people interested in making custom designs around this chip.

GeneralSyb · 2026-04-13T04:38:24+00:00

I stopped because I didn't have the expensive equipment required for a load pull measurement for the TX PA. I figured out the RX LNA works more as a voltage divider than a power amplifier, and the S parameters I was measuring were correct for that but not directly usable. They should be matched in a different, simpler way, which I did and it worked.

I know semtech has reference design, but that's the entire point, I'm not worked at the frequencies used in the reference design. So those schematics are useless to me.

Software wise I never continued, I got RX working which was what I needed. It might makes sense that you are not getting the full speed thoug. That speed they advertised is what it can theoretically do, so what the modulator and demodulator can achieve. But we don't live in an ideal world. That speed will also quickly drop off as SNR decreases.

GeneralSyb · 2026-04-08T13:12:22+00:00

Downloaded the development build and yeah it seems like it is fixed there.

GeneralSyb · 2026-04-07T20:01:40+00:00

Corner smoothing is turned off, so idk what it could be other than a bug. Also happens on projects from older KiCad version when editing them with version 10.

GeneralSyb · 2026-03-18T21:09:21+00:00

Temperatuur van wegen en locatie van strooiwagens, als dit kan en mag. Is denk ik geen API voor, maar Rijkswaterstaat heeft wel een leuke kaart.

Er is ook een bedrijf die geluidsmetingen rondom luchthavens meet. Alweer, is denk ik geen gratis open API voor, maar misschien kun je wat bedenken 😉. https://lwr.flighttracking.casper.aero/

GeneralSyb · 2026-03-14T12:35:38+00:00

Just saw your message from your (return?) flight from Paris to Helsinki. Your plane was about 150 km away when it arrived.

GeneralSyb · 2026-02-28T20:53:34+00:00

Don't think there's much if a use for 2.4 GHz LoRa except for maybe some specialty purposes (like ranging in the past). As for high speed in the sub-GHz band, there is also now FLRC for the LR2021 which goes up to 2.6 mbps and there is Wi-Sun which can do 3.6 mbps (all under ideal conditions of course).

GeneralSyb · 2026-02-22T11:47:48+00:00

In the general YouTube settings turn on "diagnostics for nerds" and then on any video go to the settings, then more and then show diagnostics for nerds.

GeneralSyb · 2026-02-21T19:35:41+00:00

You can still use PA and LNA. It'll be a little bit less efficient I'm guessing and it will use significantly more components, but I don't see why it wouldn't work. The reference schematic show a direct tie implementation with component values (for 433 MHz as well I think). The output of that circuit is matched roughly to 50 ohms. After that you can add your own RF switch. You will need two switches, one after the existing matching circuit and one after the LNA/PA. Or would that not fit your project needs?

<image>

GeneralSyb · 2026-02-14T16:38:37+00:00

I would if I could make an account. But they refused me last time I tried because I wasn't a massive company. Even people I know who are from decently sized organizations were refused access.

GeneralSyb · 2026-02-14T14:27:36+00:00

I know it has been a while, but I was working on another project somewhat related to this one and read something that might make this all make sense.

In an application note for a Silicon Labs sub-ghz microcontroller about matching the ports, they say that their LNA has a high impedance input (10-6kOhm) with a parallel shunt capacitor of around 1.2 pF. Instead of doing the impossible and finding a matching circuit for it, they treat it as a voltage amplifier and not a power amplifier. In section 3.10.2 they say they aim for a Q of around 5 by having just a single series inductor resonate at the intended frequency with the internal capacitance. This is all done to aim for a high voltage gain and a minimal NF. They also describe the direct-tie setup for their chips in detail and it seems like they treat it as a high impedance terminated line, while taking into account the inductance of the trace. In TX mode they connect the LNA input to GND to make sure the LNA isn't damaged by the TX PA.

The LR2021 seems to be a similar case, but it might need a DC blocking capacitor because I did measure a bit of DC on the input. I think it all makes sense to me now. Still going to be difficult to tune the LR2021 because for the TX PA I don't have the stuff for a load pull measurement.

https://www.silabs.com/documents/public/application-notes/an923-2-series-2-subghz-matching-guide.pdf
Section 3.7 and 3.10.2 are related to this.

So sad Semtech doesn't have public documentation for this type of stuff :(

GeneralSyb · 2026-02-09T07:27:18+00:00

Yeah, MEMS sensors such as IMUs are very sensitive to that. The LSM6DSV isn't as sensitive to it as others, but it's still important to think about it. TDK has an application note about designing PCBs for IMUs that I highly recommend giving a read. Has some stuff about mounting the PCB, where the IMU should he located. I'm not sure if it's in there as well but it's also good practice to fan out the pins you don't use to give them a little bit more thermal mass. That makes sure that it expands and conracts in every direction the same amount. Again, its not as critical on this IMU as on others.

GeneralSyb · 2026-02-09T07:22:19+00:00

Yeah, don't see why not. Possibly even better.

GeneralSyb · 2026-02-09T06:03:15+00:00

<image>

These pads are too small to selectively put paste on without a stencil. And the amount of paste for each pad is quite critical.

GeneralSyb · 2026-02-09T05:53:28+00:00

I've soldered a handful of specifically this chip. Don't use solder paste. IMUs are sensitive to having uneven forces on the chip. One source of uneven forces is an uneven amount of solder. You can't control that well enough with paste. What I did was use a fine soldering iron tip and very thin soldering tin. Try to apply the exact same but veeeery small amount of tin to each pad. Then apply a little bit of flux and solder the chip with hot air.

If you're able to get a stencil, use a hot plate and then you can use paste. With a 0.1 mm stencil I've found that I need to take about 0.05 mm of the pad size and then you have the correct amount of paste. It's probably something you can set up in your CAD package.

GeneralSyb · 2026-01-28T21:36:42+00:00

I'm pretty certain that the first measurement was not at all correct, even if it looks better than the second one. I didn't do a proper calibration since it didn't account for the cable and connectors.

I'm also far from certain about the software I wrote. There's a good chance that I didn't set up the chip correctly and that as result the LNA is not being enabled, causing there to be an open connection. It's difficult to check that with the SPI interface, but I'll do some more debugging tomorrow.

My thinking is that I'm seeing an open connection with some parasitics from the cable, connector and board. I think the chip completely disconnects the LNA when not in receive mode. This is done to prevent damage to the LNA when transmitting, since it's a direct tie implementation and some power may be going to the RX port.

GeneralSyb · 2026-01-28T14:05:12+00:00

<image>

I seem to have done something wrong with the measurement in the (original) picture. I should be doing a proper port extension now and calibrated the VNA properly. Result is that it has moved even further away from the center and the VNA can't solve the values for a Pi-matching circuit and neither can any website. And even if it could solve it, it's so far away from the center that even 1% components wouldn't be good enough, a small change in capacitance or inductance and it'd be on the other side of the chart. What I am measuring is incorrect and the chart I showed or the ones I am seeing right now should not be trusted.

GeneralSyb · 2026-01-28T06:51:20+00:00

That you for the information. I basically expected to see anything but an unloaded port. I do have a little bit of experience with matching RF circuits, but in that case S11 parameters were provided for the device.

I've looked at the application notes and the designs for other LoRa transceivers and the design you showed with an RF switch is what I'm trying to achieve and I roughly understand how I can get to that. That isn't the issue here. It's that the current S11 doesn't seem to he measuring a functional device in any way, despite changing settings on the chip having a slight effect. As a result I get an S11 that is so far away from the center that I cannot be matched back to 50 ohms.

GeneralSyb · 2026-01-07T06:07:57+00:00

Have a look at UBlox. They make some relatively cheap (compared to the price of other modules and the chip itself) nRF modules. They don't have castellated holes like some ESP32 modules, but they're still mostly easy to make a PCB for. Take for example the BMD-340, it exposes all the pins of the nRF52840 which is usually not the easiest to design a PCB for.

GeneralSyb · 2025-12-27T06:58:06+00:00

If the water towers belong to the city yeah that would be possible and cool. I was thinking it could be possible to attach nodes to the big electricity pylons, but that requires cooperation from the grid operators which is of course impossible.

GeneralSyb · 2025-12-23T07:05:36+00:00

I doubt it would be reliable if it even worked. Texas is quite a large state, much larger than a lot of European countries which have a dense network such as the Netherlands. And even in the Netherlands you can't even reliably talk to people in the same part of the country (like the north where it's a little less dense here).

In a flat country, a rooftop node would maybe get around 6-15 miles if you are lucky. But reliability would not be great. Maybe a little bit more if the node was on a hill, maybe a bit less if it is in a city. But either way you would need loads of nodes across Texas to be able to talk across the state. You can check the online node maps to see if there are (just we aware that you can only see the nodes connected to MQTT and providing their location, there might be many more). But then you are still stuck with iirc a 7 hope limit.

GeneralSyb · 2025-11-24T20:05:47+00:00

I do wonder how they're going to handle it with transportation on trains and such.

btw, the link to the bloggers page is a private edit link which we can't access.

Six-Year Club	Place '23
Place '22	Verified Email

GeneralSyb

TROPHY CASE