<azonenberg>
ok so the picovna is FINALLY set up after a bunch of pain getting vmware to play nice
<azonenberg>
and fighting a bunch of windows issues unrelated to the pico software
<azonenberg>
i'm characterizing the xaVNA SOLT kit for lulz
<azonenberg>
The thru has -8 dB S22 at 2.8 GHz lol
<azonenberg>
that is pretty bad for what is supposed to just be a SMA coupler
<azonenberg>
although i want to double check i had it torqued right etc
<azonenberg>
Actually its looking like the N cvonnectors were too loose
<azonenberg>
i dont have a N torque wrench
<azonenberg>
Clearly i need one
<azonenberg>
oook so now that that's taken care of i'm finally ready to start doing some real measurements
_whitelogger has joined #scopehal
<azonenberg>
OK so *this* is very interesting
<azonenberg>
it's looking like the 3-resistor probe design actually outperforms the same board reworked to have 6
<azonenberg>
unsure if rework is at fault or if my sonnet sims were more right than i thought, or what. Still fine tuning the setup for holding probes in the fixture etc
<azonenberg>
The 3-resistor probe is flat +/- 1 dB to 1.2 GHz, then peaks to +1.4 dB at 1.24 GHz and down to -2.6 dB at 1.5 GHz
<azonenberg>
(this is also without de-embedding any effects from the test fixture, which i hope are minor but am not certain)
<azonenberg>
and sorry i meant -1.6 dB at 1.5 GHz
<azonenberg>
Then -3 dB rolloff is finally hit at at 2.46 GHz
<azonenberg>
The 6-resistor probe is actually a lot less flat. -0.4 dB initially then peaking to +3.4 dB at 700 MHz
<azonenberg>
back down to 0 dB at 1.1 GHz then freefalls past that
<azonenberg>
By 2 GHz it's at -9 dB
<azonenberg>
The TA061 also has strong peaking, unsurprisingly. Down almost a dB at 100 MHz, +2 dB of peaking at 800 MHz, then freefalling to -3 dB at 1.13 GHz
<azonenberg>
with a fairly smooth rolloff after that
<azonenberg>
The picoconnect 921 is flat +/- 1 dB out to 2.7 GHz, slight peak there, then rolloff with -3 not hit until 4.4 GHz
<azonenberg>
cyan = $1K 20:1 Pico fancy probe, pink = $330 10:1 Pico basic probe, blue = my probe with the 3-resistor attenuator, red = my probe with 6-resistor attenuator
<azonenberg>
Blue is looking like the winner right now. Is it perfect? No. But it's flatter than the TA061, which is what i'm competing with, and has significantly higher bandwidth (-3 dB at 2.4 vs 1.1 GHz)
<azonenberg>
this is using the Z-ground, btw
<azonenberg>
I got even better results with a different grounding setup though
<azonenberg>
That one was flat +/- 1 dB out to 1.7 GHz
<azonenberg>
hmm, the 6-resistor probe with a shorter tip and better ground is better too. I get slight attenuation (<1 dB) up to 1.2 GHz, slight peaking up to 1.8 GHz, then rolloff to -1 dB at 1.9 GHz and -3 at 2.02
<azonenberg>
also the PMK tips seem to not fit these sockets super snugly. Which I'm not thrilled about at all
<azonenberg>
i guess worst case i could glue/solder them in place
<azonenberg>
but i might still want to explore different socket options or something
<azonenberg>
i'm still seeing massive differences from run to run and unsure on cause
<azonenberg>
Some is likely the way i'm holding the 6R probe as it's not in a shell