azonenberg changed the topic of #scopehal to: libscopehal, libscopeprotocols, and glscopeclient development and testing | | Logs:
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<_whitenotifier-5> [scopehal] sam210723 synchronize pull request #396: Add binary capture file parser -
<_whitenotifier-5> [scopehal] sam210723 reviewed pull request #396 commit -
<_whitenotifier-5> [scopehal] sam210723 reviewed pull request #396 commit -
<_whitenotifier-5> [scopehal] sam210723 reviewed pull request #396 commit -
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<miek> is there any way to skip the connect dialog when launching glscopeclient?
<sam210723_> passing a bad scope string works
<sam210723_> eg. "0:0:0"
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<azonenberg> sam210723_, miek: long term the whole startup/welcome dialog is going to get totally redone
<azonenberg> Katharina was supposed to be working on that, then disappeared
<azonenberg> She was out for several months with covid so not sure if complications from that, or just busy at work / lost interest
<azonenberg> i want to be able to connect to scopes, load recent scopesessions, reconnect to recently used instruments, activate demo mode with an easy button, etc
<azonenberg> But i've been too busy with other stuff to touch that
<azonenberg> sam210723_: also with those new commits are you ready for me to review and merge your contributions?
<azonenberg> or are there still open action items you want to address?
<Famine-> azonenberg, any suggestions for cheap/semi cheap 1000:1 probes ? (low energy, maybe ~200uJ)
<azonenberg> 1000:1? how high voltage?
<azonenberg> and are you looking for 1M outputs or 50 ohm?
<azonenberg> a 49.95K resistor in series with 50 ohm coax would form a 1000:1 transmission line probe, and in theory you could use it up to 5 kV with a normal 50 ohm 5V scope input. But i'd be worried about the resistor arcing over and frying the scope and/or me
<Famine-> ~50kV
<azonenberg> So you definitely want a 1M ohm probe then
<azonenberg> alternatively you could do a 10K:1 (or more) resistive divider probe
<azonenberg> the other problem with a resistive divider at these extreme values is fast edge
<azonenberg> since you mentioned uJ i assume this is for pulse applications
<azonenberg> even a few fF of shunt capacitance across the resistor would allow high voltage transients through
<Famine-> yea, ford coil pack testing. the lovely design of the PCM means if the coil pack dies then the driver fets fry and its $2500 for a new pcm lol
<azonenberg> if my mental math is right with a 1000:1 probe you've got 30 dB of attenuation, so you'd need *extremely* flat frequency response out to well past the highest freq in the signal to avoid overvolting the scope
<azonenberg> 6 dB of peaking doubles the voltage the scope sees
<azonenberg> Which is not that much of a non-flatness, proportionally speaking, on a 30 dB probe
<Famine-> ugh lovely and i'll probably have harmonics >500MHz
<azonenberg> have you ever looked at the derating curve for a typical scope probe?
<azonenberg> they reduce the max voltage greatly as freq goes up, in part because of this
<azonenberg> High voltage *and* high frequency is hard
<Degi> Also the loading can be relatively high from probe capacitance
<azonenberg> You could probably add lowpass filtering to remove some of those harmonics
<Famine-> good to know. i thought oh this will be easy i only need 10MHz
<azonenberg> but you can't use a normal matched 50 ohm filter
<azonenberg> because 50 ohms to DC with this kind of power level would be insane :p
<Degi> Like a pF at 10 MHz and 10 kV can do 6.2 kVAr load
<azonenberg> Famine-: Data point: a 500 ohm 0603 resistor is 474 ohms at 500 MHz
<azonenberg> and that's a flip chip RF resistor
<azonenberg> the FC series 1K ohm with wraparound terminals is 894 ohms at 500 MHz
<azonenberg> So you're down by 10% which is not quite as bad as i thought. but still, as resistance goes up with the same shunt capacitance
<azonenberg> the proportional change goes way up
<azonenberg> typical resistors in the megohms will... not be megohms at hundreds of MHz
<azonenberg> now, going with big fat carbon composition or even wirewound (deliberately increasing L) will definitely improve that vs an 0402
<azonenberg> but this is not something you throw together casually without a LOT of testing and measurement
<azonenberg> high power RF is something you can easily screw up quite badly
<Famine-> < even better is fords COP system is always hot
<Famine-> looks like i'm stuck not cheaping out and need to order something like a tek P6015 off ebay
<azonenberg> Even if you do get a pro HV probe, check the datasheet carefully for high frequency derating
<azonenberg> like i said most are not meant for pulse applications
<Famine-> yep even the P6015 is <1kV @ 100MHz
<azonenberg> even single or double digit femtofarads of capacitance are a big deal at these freqas
<azonenberg> freqs*
<Famine-> i am starting to have a serious love hate relationship with analog design lol
<azonenberg> lol
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