<azonenberg>
S11 and Zin measurements from the first four AKL-PT2 units
<azonenberg>
A68-001 is quite the outlier, going to remeasure it and see if it was a bad soldering job or maybe if something is wrong with it somehow
<azonenberg>
I'm switching to a different serial number scheme to fit the very tiny space available on the underside of the FR4 stiffener (the only part of the probe with enough space for a S/N)
<azonenberg>
A = 1 year since 2020, 68 = day of year, then 3-digit serial within that day
<noopwafel>
that is a pretty fun outlier
<azonenberg>
This is measured across an open circuit
<azonenberg>
what's interesting is the frequency of that null, and the fact that all probes have a null there
<azonenberg>
but A68-001 is much worse
<azonenberg>
that frequency lines up nicely with a reflection off the SMA
<azonenberg>
So I think it's a mismatch there
<azonenberg>
I did use a lower grade terminator for measuring 001 then switched to a nice one. I dont think I'd get 0.8 dB more reflection through two resistors from a cheap terminator but i'll definitely remeasure
<azonenberg>
I'll also get a lot more data once my next batch of 25 SMAs arrives later in the week
<azonenberg>
when i have 20+ probes worth of measurements I can draw much more conclusions about yield, consistency, etc
<noopwafel>
I look forward to more stories, if nothing else this is all v.educational :)
deltab_ is now known as deltab
<azonenberg>
also i just compared all of the PT2's to the pico 921
<azonenberg>
even A68-001 has lower loading than it
<azonenberg>
Which makes sense because i don't have the stub from the tip needle
<miek>
azonenberg: could i get a copy of the s1ps for those? i want to have a play around with doing transforms on the data
<azonenberg>
I can't fully assemble the rest of the probes until I get the SMAs (current ETA is Friday) but I might do SMT-only assembly on a panel or two tonight or tomorrow
<azonenberg>
002 is the outlier, not yet sure why. It fails the 6 GHz bandwidth requirement (dipping below -23.5 GHz from about 4.5 to 5 GHz then a few times after that)
<azonenberg>
but 001, 003, 004 are all >6 GHz probes with fairly smooth rolloff
<bvernoux>
it is very flat too
<bvernoux>
the blue is a bit off compared to other it is strange but the scale is very small too
<azonenberg>
I'm going to be testing a lot more units in a few days
<azonenberg>
Friday I have 25 more SMAs coming
<azonenberg>
I stopped at four this time because that's all i had connectors for
<azonenberg>
but i have 241 more bare PCBs
<azonenberg>
I'm planning to do SMT assembly of two panels today or tomorrow then on friday put the SMAs on them and measure
<azonenberg>
that should give me enough units to open initial sales, as well as enough test data to write a datasheet with reasonable limits
<azonenberg>
it's modeled on the AKL-PT1 datasheet, section 7/8 are blank awaiting more test data
<azonenberg>
6 is missing some data
<miek>
what is the test setup for these measurements?
<azonenberg>
Descriptions of the test setup is one of the sections of the datasheet I haven't written yet. actually talking to an artist to go draw up some diagrams as they'll be more clear than photos
<azonenberg>
the tl;dr is that the S11 curves are measured with the probe soldered across the end of a 6mm long open circuit line
<azonenberg>
and the S21 curves are measured with the probe soldered across a 50Ω termination
<azonenberg>
I will also have typical rising edge waveforms with cables de-embedded. The holdup there is that I need a scope with >6 GHz bandwidth to accurately measured that :p
<miek>
and the cal ref. plane is at a connector on that open line?
<azonenberg>
No
<azonenberg>
well
<azonenberg>
calibration plane is at connector but i did an extension to the end of that open
<azonenberg>
so the impedance numbers are based on the shifted ref plane
<miek>
aha ok
<azonenberg>
For the S21 measurements since the fixture i use there is a bit longer, I made a sonnet model of the fixture
<azonenberg>
tuned some numbers to match VNA measurements of a similar thru line
<azonenberg>
and de-embedded that s2p from the measurement
<azonenberg>
plus a fixed ref plane shift to remove the electrical length of the SMA
<azonenberg>
So basically in both cases the measurement plane should ideally be at the tip of the probe
<miek>
for the s11 measurements, is the probe still setup with some length of coax going back to port 2?
<azonenberg>
No. There's a 50 ohm termination across the SMA and port 2 of the VNA is floating
<miek>
i've also been reading Joel Dunsmore's book again after he was on the amp hour, there's some really cool stuff in there about time domain gating & automatic fixture removal
<bvernoux>
the link on lecroy article about ripple is interesting
<bvernoux>
but here ripples are very localized between 2.4 to 2.6GHz
<bvernoux>
on S11
<bvernoux>
on S21 yes it like like what is described by lecroy article