<azonenberg>
The enclosure is just a little too snug, i pinched the pcb a bit trying to get it in which might be the source of some of the imperfections (but probably not related to the huge hump)
<azonenberg>
The resonance seems about the right length to be a reflection off the SMA launch caused by it not being super well matched
<azonenberg>
Which isnt surprising, i did the stackup design based off a pretty rough estimate of the polyimide properties
<miek>
azonenberg: can you use time domain mode on your VNA? iirc it has it but was buggy/unstable?
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<azonenberg>
miek: so basically the issue is, it requires using harmonic rather than linear point spacing
<azonenberg>
Which i don't like doing, because it's less useful for stuff like de-embedding
<azonenberg>
and any time i change the number of points, start/stop of the sweep, etc i need to recalibrate (duh) but it also does some incredibly slow internal operation that takes about 30 minutes
<azonenberg>
i have no clue what in the world is so wrong with the firmware/software to need that
<azonenberg>
but the progress bar barely looks to move, the entire app locks up because they don't do it in a background thread
<azonenberg>
so generally i try to set it up once, keep the software running for weeks at a time, and always have 10001 points linearly spaced from 300 kHz to 6 GHz
<azonenberg>
and just never touch anything because it's so painful to reconfigure
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<azonenberg>
Kenley: so you're "kench" on github right?
<Kenley>
Correct.
<Kenley>
I'm not really much of an IRC person these days.
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<azonenberg>
lain Kliment kc8apf: So i just finished another test of the AKL-PT2 prototype
<azonenberg>
it turns out mounting is actually extremely critical to get good performance out of it
<azonenberg>
In particular, you cannot mount it flat on the PCB because you get capacitive coupling through the polyimide substrate to the signal trace and ground plane from the flip chip resistors. It's only 100um thick so the coupling is quite strong
<azonenberg>
When i glued a nylon washer under the board body to space it up a bit, the response flattened out massively. Long term plan is to use an 0.8mm or so FR4 stiffener to accomplish the same goal, but preinstalled from the fab
<azonenberg>
Kliment: I'm putting a fr4 stiffener on the other end of the PCB for the SMA connector to provide mechanical rigidity
<azonenberg>
once i do that, adding a second one where the washer is in this photo is a piece of cake
<azonenberg>
i am gonna be doing a new board spin with immersion silver anyway because this long line has a lot of loss which i think is at least in part due to the enig
<azonenberg>
And at least one respin of the enclosure with mechanical improvements
<azonenberg>
The Dymax UV urethane i'm using actually seems to work really well for holding probes on
<azonenberg>
it's UV cure so if you screw up applying you can easily rework before curing
<azonenberg>
once cured it's strong, but it's weak enough that if you apply enough shear force you can shear it off the board without damage or residue
<Kliment>
yeah it's a lovely glue
<azonenberg>
you've used the same stuff?
<azonenberg>
Dymax 9-911?
<Kliment>
I think I've used the loctite equivalent
<azonenberg>
ah ok
<Kliment>
same properties
<azonenberg>
the dymax stuff is also blue/longwave UV curable
<azonenberg>
so a standard gel nail curing system will cure it
<azonenberg>
no need for hard uv-c etc
<Kliment>
yeah they come with a little UV pen
<azonenberg>
ah ok yeah mine did not, it just came in a giant syringe clearly meant for automated dispensing
<azonenberg>
so i repackaged in smaller 10cc syringes because i couldn't find any opaque 1cc ones