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Re: Am I in the right track ?
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1) Do you have the eval board? (Always useful to look at a "known good" implementation)
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2) I'm not sure it's expecting copper under the coil. The figure in the data sheet sort of looks like only the "shaded" part has ground plane. 3) As others have commented, Make your connector to trace *really* short. (as in <1 cm). Then calibrate at the end of your longer test cable. Bear in mind that the cable *will* have an effect on the pattern and Z, so try moving it to different positions and seeing how much difference it makes. 4) ferrite chokes *might* help, but might not. Choosing an appropriate mix is tricky - you need something that "works" at 900 MHz, and random cores intended for suppression of VHF noise might not do much good at 900 (people run into this when testing GPS antennas at 1.2 and 1.5GHz). Look at the FairRite catalog - you want large loss (R) more than large X at your frequency of interest. A quick check shows that you might be looking for a 61 (200-1000 MHz). 61 peaks at about 250 and rolls off gradually as frequency goes up (and the plot only goes up to 900) As for stretching or shrinking? (or dropping blobs of wax on it - something that's also done). Most people optimize for received field strength in the assembled unit, rather than adjusting the impedances. What is the *real* output Z of your LoRa module? (yeah, nominally 50 ohms for design, but really? who knows). Then, after you've tuned it up, you can dismantle it and measure it. The matching CLC matching network might be to accommodate some other modules with different Z. This kind of thing has a LOT of empiricism in it, unless you've got access to fairly fancy design tools like HFSS that can model it. Note the problems Apple had with the iPhone's antenna (For which the solution was, "don't hold it like that, because it shorts out the feedpoint") -----Original Message-----
From: <[email protected]> Sent: Feb 23, 2025 6:35 PM To: <[email protected]> Subject: Re: [nanovna-users] Am I in the right track ? Once again, Thanks to all of you for your inputs. Poorly translated from french, I would say that I did not know in what type of gearbox I was going to put my finger in ! Well, I ran some other experiments tonight. Here is what I've found. The antenna is an helical monopole where the pcb copper pour serves as the antenna ground plane. I really made sure to follow the manufacturer's layout recommendations. The feed line (as pictured in my original post) shows the feedline also, designed as suggested by LINX. I've included the PI matching network at the very end of the ground plane as also recommended. This is the datasheet link: ;DocNm=ant-916-hexx-ds&DocType=Data+Sheet&DocLang=English&DocFormat=pdf&PartCntxt=ANT-916-HETH I did what you guys suggested. I've cut a 6in piece of RG-174 and the used a 30cm RG316 extension I have. I did the SOL at the end of the extension and added a delay of a few pico seconds for the remaining piece that attach to the pcb. @Roger Need: Thanks, Oh, I forgot to mention some board details. I attached pictures of my pcb. My cable is attached where the LoRa radio module will go, as seen on the bottom side. The feedline to the antenna should be a 50 ohms impedance feedline, it goes to a matching network (as recommended by the manufacturer) and then to the antenna. The ground plane dimensions are specified and the distance of the antenna from the ground plane border also, which I've respected. It is a 4 layer PCB. Layer #2 has a ground strip line under the trace that goes along with it that should form the 50 ohm line right down to the antenna itself. @John, Thanks for your input. could you point me out to some ferrite cores ? I would not know what to look for exactly. If you know some specs and a good source for it, that would be awesome. Well, I get some interesting result but I'm not sure if I understand what is happening. As you can see with the pictures, if I hold the board in my hands, I get what I would call a "proper" response. But once I lay the boar on the top of the pole, the signal looks like crap. Putting the pcb back into its enclose does not make any significant differences, good or bad. By holding it and then read something better, does that I mean that my body becomes the ground plane it needs ? Would that mean then that the pcb ground plane is not sufficient in size ? That would be weird as the pcb ground plane is slightly larger than what is recommended by the manufacturer. Once again, thanks to all of you for lighting up lantern, I truly appreciate your advices. RF has a steep learning curve ;) Nicolas |
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