Wow ! Thank you so much to every one for taking your time in helping me. I truly appreciate it.
@Siegfried @John
I finally did it. I've cut down my RG174 down to the shortest length I could (35mm). I'v calibrated at the end of an RG316 I have, then connected the "board-to-pcb adapter". I added a 180ps Edelay. I tried to double the value (for round trip) but with no differences.
@WOLEV : The Whole board measures 100mm and the ground plane measure 74mm in length. I'm realizing at writing this this could be a part of the problem ? If this is a 1/4 wave monopole, then it should needs the equivalent as a ground plane, that could mean my ground plane is not long enough ? it should be 84 according to the datasheet. mmm I may have to reorder some pcbs !
@Jim
1- No, unfortunately I don't have the evaluation board. I'm on my own, I know almost nothing in RF !
2- This antenna is designed for high volume applications. In my case the "high volume" will be 2 units !, Anyways, this antenna is sold in either through hole or surface mount. There are squares as pads for the surface mount version. I may have to remove them as I use the through hole one.
Unfortunately, I won't have access to any design tools in that field. Even if I had one, I would not know ho to operate it to extract valuable data...
If my LoRa (20mW of extreme power !) module is not 50Ohms on the output, I will never know and there won't be any ways I'll be able to measure it.
@Roger
1)My pcb stack is a standard 4 layer from JLC PBC with controlled impedance option selected. They offer the calculator for the appropriate trace width. As per the datasheet of the antenna, the transmission line from the RF module to the antenna itself has a ground plane on layers 2 and 3 to offer the return path for the feedline. This is what is recommended in the datasheet. This is what I did and know I understand the reason. So, in theory, from the LoRa module to the antenna, this should be a transmission line and not a part of the radiating element. Thanks for pointing out ;)
2)With my short 35mm adapter tonight, I tried 180ps and 360ps as Edelay with no differences.
3) I tried yesterday to calibrate with the cable shorted, opened and then loaded with a combination of a 47 + 3 ohms of 0805 chip resistor I had on hand. I don't remeber exactly and I don't have any pictures but by memory it gave me negative values as the R. Assembling two chip resistor to make one, not the greatest idea. I will have to order som 50Ohms chip resistor .
Question : Can I use 0805 it should definitely be 0603 ? I've somewhere there could have capacitance effect on a too big of a chip.
4) Thanks for the info on ferrites. I'll give them a look.
So here is my progress so far:
- Tonight I'v cut the cable to 35mm but calibrated at the end of my 30cm RG316. Look at the pictures to see the results.
- I've realized that my ground plane may be too short and have to modify the boards and order new ones.
- I've ordered an RF inductor and capacitor kit for the CLC matching network. I'll give it a try and see from there where it goes.
To be continued...
