Since you are dealing with SM inductors, I remembered something I've
learned and practiced for a couple of decades. In mounting SM inductors it
matters how they are constructed internally. The suppliers do not publish
this data. As such, I have always required the PCB layout engineers clean
the "ground" plane from under any and all SM inductors. Depending on the
internal construction of the SM inductor, the close proximity of planes and
traces immediately beneath the inductor will alter its characteristics and
in-place inductance. Even on 2-layer boards at microwave frequencies, this
is a concern. I may even require cleaning the common plane and all traces
from any of the layers under the SM inductors.
Instead of using your 10 nH SM inductor, a 0.5-inch of AWG #18 solid copper
wire would yield something very close to your target inductor. Install it
between the pads intended for your SM inductor and make a very wide hairpin
out of the wire. Even a hair pin will introduce additional inductance over
a linear straight conductor, so you may require a bit less than
0.5-inches.
Dave - W?LEV
On Tue, Mar 18, 2025 at 2:56?AM Nico via groups.io <nicolassimard=
[email protected]> wrote:
Roger,
Thanks for the idea. I already tried sending them an email a while ago for
that exact request ! The phone is still ringing, nobody answered yet at the
other end ;( But I should throw the fishing stick once again using my email
address from the office, that would look more serious... I'll let you know.
In the meantime, I've conducted one more test tonight, with interesting
but a little disappointing results. arrrrgg, I'm missing the knowledge and
there may be something obvious I don't get. Maybe someone has the right
batteries to fit my torch !
I've cut on end of a 36" long RG316. I soldered it to the PCB. I
reinstalled the pcb in its case and made the cable going through a hole on
the underside. Straight out the box I wrapped the cable 3 times around a
Fair-Rite 61 material that has a 0.9" inside diameter. I connected this to
another 12" premade cable then to the VNA just to give me some length. That
is for sure, I took the time to calibrate OSL right before mounting all
that. BTW the load has been done a 50 Ohm 0603 chip resistor at 0.1%
accuracy spec (at 3$ a piece !!).
Picture 1 : Test setup (the same as all my other tests)
Picture 2 : Measurement in this condition (no matching network, only a 0
ohm resitor to pass through)
Picture 3 : Data from the VNA plotted in SimSmith,
Picture 4 : Expected reading (or close) after putting a 10nH in series.
Picture 5 : Actual reading I got after installing the inductor.
Every time I tried to correct/match the antenna it gave me horrible
results like that. There must be something obvious I don't see.
At the end, I do not expect to achieve the 1.5 VSWR flat as in the
datasheet. It is a personal project after all. But if I could at least
match it down to 2, I would be more than happy. This module will be
installed in my backyard and the receiver will be at less than 50 feet. It
is more a matter of learning new things. The one thing I want to avoid
though, is to make it work by pure luck without knowing why.
I'm searching for a needle in the haystack, can someone lend me a metal
detector please !!
Nico
--
*Dave - W?LEV*
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Dave - W?LEV
