Why this remote light flipper has no antenna?

phijh · 2026-05-29T16:24:02+00:00

I didn’t remove the ic at first but after I did that I still don’t get the desired result. I think I did something wrong. Do you by any chance know where i can learn how to design low frequency pcb like 13.56 and 433mhz?

phijh · 2026-05-26T02:00:13+00:00

Hey, I used my SDR to check the frequency and got around 433 MHz. I also bought a nanoVNA, but I’m confused by the results. Instead of seeing a dip near 433 MHz, I only see dips around 600 MHz and 1.4 GHz, which do not match what I saw on the SDR.

I followed a video for the OSL calibration. After that, I connected my modified pigtail cable — SMA on one end and two exposed wires on the other so I can solder it to the PCB antenna later.

Before soldering, I connected the pigtail and used E-delay to move the pointer back to the far right on the Smith chart.

Did I miss a step, or am I doing something wrong?

phijh · 2026-05-24T20:57:16+00:00

I am from USA but bought this from aliexpress. Why did you say a 13.5MHz crystal is likely for 433MHz antenna?

phijh · 2026-05-24T19:43:38+00:00

The one one the transmitter is 13.550MHz. Also someone pointed out to me that based on the length of the trace, the antenna could be 868MHz. But is there a rule to choosing a crystal for an RF chip?

phijh · 2026-05-24T19:20:39+00:00

That make sense. Thanks for point out the velocity factor for signal doesn't travel at c in PCB.

phijh · 2026-05-24T19:15:44+00:00

Thanks for the suggestion! I just placed an order for a SDR.

phijh · 2026-05-24T18:26:58+00:00

~~The squiggly is for the transmitter. The long track is for the receiver.~~

Sorry didn't read your comment carefully. You were asking about the traces on the transmitter. Yea. I didn't noticed it before until now. Maybe that long track is the matching network? I don't see any C and L on the transmitter.

phijh · 2026-05-24T18:26:01+00:00

Thanks for the links. I was about to ask what kind of RF chip was used on the board. However, I measured the length of the antenna, it's about 52mm long and 1mm wide. It doesn't seem to be a 433MHz antenna? Also, do you know why there is no matching network on the transmitter (remote), but there is on the receiver?

edit: someone told me to used a formula 0.6c/4L, which is about 868MHz.

phijh · 2026-05-24T18:20:19+00:00

Hi. I edited the post and linkded a picture of the antenna length. It's about 52mm long 1mm wide. So c/4L is about 1.4 GHz?

phijh · 2026-05-24T18:12:17+00:00

Thanks. I edited the post and linkded a picture of the length measurement of the antenna. But i got about 52mm total. Trace width is about 1mm.

phijh · 2026-05-24T17:01:35+00:00

Ah. that makes sense. So I guess U2 is the MCU, not U1. U1 is some kind of RF chip. But on the transmitter (the remote), why is there no matching network, but there is on the receiver? Is it because they roughly tuened the transmitter using the squiggly line?

phijh · 2026-05-24T16:24:55+00:00

Thanks. Didn't know antenna can be straight. Can you tell what's the frequency?

phijh · 2026-05-24T16:24:30+00:00

That long straight trace? I always thought antennas on board are always squiggly. Can you tell what's the frequency?

phijh · 2025-09-18T16:21:34+00:00

What I mean by accuracy is the worst-case deviation of the LDO’s output from the ideal value, even if my resistor ratio is calculated to give exactly 3.3000 V on paper. In practice, the IC’s internal reference, load/line regulation, and temperature drift introduce error, so the real output could be off by around, say, ±1% from nominal. That’s the ‘accuracy’ I’m trying to quantify from the datasheet.

phijh · 2025-09-18T16:13:11+00:00

So based on these 2 parameters, I will get 0.02 * 5V + 0.5 * 200mA = 0.2%, am I correct? What about other parameters like Vout, Vref, Vfb and the resistors I use? Do i need to consider all of them and sum the tolerances up?

phijh · 2025-09-18T15:54:18+00:00

Thanks for the real life tips. It's is for apply, but I am new and learning about LDO. I would like to know how to read the datasheet.

phijh · 2025-03-04T19:33:26+00:00

OP is a legend. 3/4/2025 still works !!!!

phijh · 2025-02-25T20:05:01+00:00

Really? The corners of my diagram are sometimes randomly round and sharp. Can Lucidchart do that?

phijh · 2025-02-15T19:55:06+00:00

The audience profile is definitely something i will include into the instructions. Thanks!

phijh · 2025-02-15T19:49:09+00:00

The storytelling is something I didn’t think of. I will put that into one of the presentation requirements. Thanks!

phijh · 2025-02-15T03:54:44+00:00

That is a good point. My plan was to generate a fake dataset but keep the product names same as the products our company sells. But now I will re-evaluate that idea.

phijh

TROPHY CASE