Yes, it is normal to measure near 0 ohms between the two points.
I cannot see how you will connect the SMA connector. It is important NOT to connect the ground to the old antenna. The ground pin has to be connected to an RF ground which must be a ground plane connected over a large area to the rest of the ground on the PCB. If you connect the SMA to the old antenna track it will such energy from the antenna.
Here is my top side where I only connected the center pin.
When you got away the old antenna (both the long piece and the short that goes back to ground) make sure you cut neatly along the track you want to keep. No need to cut all the way into the glassfilber. Just a sharp cut through the cupper track and then you can carefully life the unwanted up and cut it away. A scalpel or small exacto knife is a must have in the tinkerers tool box.
And then the bottom side.
Note how I have put a small piece of copper tape.
I took a sharp blade (a scalpel) and carefully scraped off the green solder mask off the edge of the ground plane at the bottom. About 2-3 mm wide. Then I put a thin layer of solder on the area and a little extra flux after.
I cut a piece of copper tape (you can use the kind you buy to put in the garden to protect slugs from eating your plants) and stuck that to the board. And then heated along the edge where it overlaps the ground plane so they get soldered together all the way. To get a good RF ground it is not enough to have a few points. Solder all the way so the copper becomes as extension of the ground plane.
Finally put the SMA connector at the right spot so you get two RF ground pins soldered well to the copper foil. And on the other side you solder the center pin. Again you will need to carefully remove the solder mask over the track so you can get a good solder joint.
The solder you see on the top side of the copper foil was where I put the solder iron to heat up the tape and the solder below. It has no function but does not harm either. The important thing is to give good heat so the solder between tape and PCB copper wets to the tape at the bottom side. It takes some good heat.
I have not seen the Ready2Use version but this is how I did it with mine and I used a standard SMA connector where the four ground pins are in the corners and the center pin in the center of the square
You can also buy a version where two ground pins and the center pin are in-line and they are nice for places where ground and center pins need to be solder to the same side of the board as well as ground on the back side. You could cover the area where the old antenna is with a copper foil that connects to the top side ground plane and solder a third pin but the other side does not easily go to good ground so for this I preferred to get the ground at the bottom. If you have the inline type you can solder two ground pins to the bottom like I did and at the top put copper where the old antenna is connected the same way to ground and solder the 3rd ground pin to the tape. And then cut off the 4th ground pin. I do not think it is needed though. What is important is not to have the old antenna track as a serial coil between a ground pin and the RF ground because it is becomes a component that resonates near the 2.4 GHz and that can eat signal but inbound and outbound.
It appears the CC2531 is also available with an external antenna from Chinese suppliers such as DIY More. However, unlike h4nc’s product, it doesn’t come with a 3D-printed case nor is it preloaded with zigbee2MQTT. In addition, I have no idea if the SMA connector is attached as well as in h4nc’s product or KennethLavrsen’s description.
@pedroborges yes this is normal, your stick is fine.
For my modded CC2531 I initially followed the steps a thread on GitHub and later it was like “approved” by this tutorial.
I do pretty much the same, but I probably spend more time with making it a perfect fit and fixing it with glue.
Before I offered these I had very much issues with reliability. All those issues where gone with this mod. All of the feedback is positive in this thread. Some new users but also users that had a stick with no antenna before and also saw the enhancement.
Also it looks like the stick from Ali with the antenna also uses the same ports.
Thanks @123 for pointing out the differences to my stick. I already saw one and the soldering doesn’t look as good as mine (the have less time per stick).
@KennethLavrsen thank you very much for your professional insights. I very much appreciate this. Always good to learn.
I will build a stick like yours and test if the values and the range gets even better (compared to my current version) or if it’s just theoretical (or not measurable).
@KennethLavrsen I don’t know much about antennas (as I said before I’m more a 3D printer and soldering guy) but look at this conversation from the tinkerer which posted this mod on Hackaday (Link in my last posting).
To me both of you (“data” and you) seem like you know what you are talking about. But I think the results (feedback) are talking for themselves and the mod is fine like it is.
Nevertheless I will try your mod to see if one of them is better.
I also saw the mod from Hackaday before I modified mine.
But I did not fancy the idea of using the old PCB antenna as a ground. It is no ground at 2.4 GHz. It is an antenna. And if you put an SMA ground pin at the end - you put an impedance in series from the connector and back to ground. In practical it may not matter that much because the other pin of the same SMA is connected to a very short track which goes to ground in a single via hole. And that is not a great ground but better.
If you already have a stick built this way there is no need to panic. It will not be a huge degradation because you have the OK ground on one of the two pins. But you could without removing the SMA add a better ground with some copper tape on the top
Something like this using the same method of removing solder mask along the edge of the ground. But be careful not to short to the capacitor or to the tracks. It is easier to do at the bottom
Or like I marked with a sharpie. Except the picture with the sharpie has the wrong type of SMA where the pins are not in-line. The Hackaday mod is done with the in-line type.
You can also remove the solder mask of the old antenna and solder the copper tape just to mechanically make it stick better.
The objective is to get a better ground so the RF is radiated from the new external antenna. Especially if you want to use a short cable to an antenna with a ground plane. For that to work the shield of the cable and the housing of the SMA need to be cold RF ground.
The advantage of having copper table on the back side is that the antenna track going to the SMA will become a short microstrip. It will not be perfect 50 ohms but it will be better than a track in “free space”.
At 2.4 GHz the wavelength is 125 mm. So everything has to be short on a PCB to work.
To those that wonder why you see a short to ground from the center pin.
There is some ceramic component that looks like a small hybrid coupler or transformer. The white component with the 6 pins. You measure 0 ohms at DC but at 2.4 GHz this little fellow is an RF component.
Got mine about week ago too and wanted to tell that the build quality is amazing!
Shipment was fast (2 days to Italy) and packaging is very good.
Great job !
I received mine a a week ago (9 days shipping to the US East Coast) and now that my Xiaomi Temp and Vibration sensors have arrived I am happy to say that the stick works great.
Got my coordinator as well! Taken into use, works like charm. Link quality reports show significant improvement compared to the “naked” stick.
Thanks again Hans!
I have sent couple of emails with questions to h4nc and he responded within minutes. Then he shipped the stick next day. Stick works great and range is also great (after some micro position tweaking it covers majority of my apartment with a single stick. And that is with crap position, stick being on one edge of the apartment).
As a mostly-software person I’m glad that I do not have to do all the soldering. So I’m very satisfied with the whole thing.
Did you consider to add an external antenna also for WiFi and BLE in order to extend esp32 range?
What I find in fact really frustrating of esp32 and BLE in general is the very limited range which make such that you need multiple device to cover for example multiple MiFlora.
I am going to make some experience with esp32 and external antenna to see if this may help: I will let you know in case
