The image that shows a SWR of 2.6 : 1 (the sixth image), all you need to do
is add an inductor in series to cancel the -j 45.6 ohms. At 916 MHz that
would be 7.9 nH.
In reality, 1.86 : 1 is not bad at all. For this sort of application, I'd
declare it complete.
Dave - W ?LEV
On Fri, Mar 14, 2025 at 3:05?AM Nico via groups.io <nicolassimard=
[email protected]> wrote:
Hi everyone,
No, I haven't abandoned yet ! I got my revised pcb (attached picture)
yesterday
1- Revised ground plane dimensions which I made the same as the test board
shown in the antenna datasheet.
2- Controlled impedance PREPREG material for the 4 layer PCB.
3- Revised feedline width for 50ohm target impedance
4- Revised return path width in adjacent layer
5- Fixed a jumper trace mistakenly placed in the feedline path.
I have calibrated O-S-L with a 0.1% 50ohms 0603 chip resistor soldered
directly on the end of the cable.
I have replaced my RG174 with a brand new RG316 36" extension from Digi-Key
I added a 6" piece of RG316 opened at one end and SMA connected to the
extension at the other.
I calibrated with everything attached to the VNA and finally soldered back
the open end right where the source swill be.
I have put 2 Fair-rite 61 ferrites on the cable, one at each ends.
I soldered a 0 ohm resistor to bypass the matching network
Picture 1 : New board front
Picture 2 : New board back
Picture 3 : Test measurement setup
Picture 4 : Antenna pcb feedline and return path
Picture 5 : Measurement with board laid on a wood plank (no matching)
Picture 6 : Measurement with board inside its plastic case (no matching)
Picture 7 : Calculated correction values from Sim Smith (High Pass)
Picture 8 : Installed L and C values (High Pass)
Picture 9 : Measurement with L and C installed
I think I have improved the antenna performance with the new board. Maybe
I have a better quality setup also. As you can see, once the board is
inside the box, it is not too bad. But unfortunately, I'm the kind of who
loves to chase perfection. Using the provided numbers from the nanoVNA, I
tried to compute some matching network values to better tune the antenna in
Sim Smith. I ordered 0603 inductor and capacitor dewsign kits at DigiKey.
Not those cheapy ones from Amazon. I installed L and C into my matching
network but as you'll see with the pictures, it did not helped at all.
1- Am I going too far, and should I stay with the values from the initial
measurements ?
2- What am I missing here ?
3- What would be your advices if I wanted to improve the response to
something close to like 2:1 VSWR ?
4- From here, I am really scratching my head...
--
*Dave - W?LEV*
--
Dave - W?LEV
