azonenberg changed the topic of #scopehal to: libscopehal, libscopeprotocols, and glscopeclient development and testing | https://github.com/glscopeclient/scopehal-apps | Logs: https://libera.irclog.whitequark.org/scopehal
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<azonenberg> Also, more probe progress: got price information back from the vendor I'm using for prototypes of the lossy coax cable for the AKL-PR1, the solder in R-C divider probe
<azonenberg> going to be ordering a bunch of prototype cables with SMPMs at one end to connect to a probe head much like I have for the PT5, then BNC at the other end
<azonenberg> The prototype compensation box will live in https://www.mouser.com/datasheet/2/94/BNC-KIT-2.6MF-1650454.pdf
<azonenberg> it's a single stage compensation network with a 5.5 - 30 pF capacitor in series with 68 ohms to ground
<azonenberg> But i expect to go through several iterations of that design. the box has a ton of room for more complex networks, this is just a prototype
<azonenberg> PCB and components for compensation box are ordered, probe head design is still in progress but shouldn't take too long
<azonenberg> At which point the big question is just how fast we can get the special lossy coax once the order is submitted
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<Degi> What is the lossy coax for?
<azonenberg> Degi: building a 10:1 probe for 1meg high-z inputs, like a standard passive scope probe
<azonenberg> you need high ESR coax to reduce reflections because the cable is not impedance matched to 1M ohms
<azonenberg> so you get a reflection off the scope input
<azonenberg> the lossy cable helps damp that out
<azonenberg> it doesnt disappear entirely, it's an unavoidable issue w/ 1M ohm probes afaik
<Degi> Ah, do they make special lossy cables for that
<azonenberg> Yes. but they're extremely hard to obtain
<azonenberg> because there is essentially no use for one other than building a 1M ohm probe
<azonenberg> and all the OEMs make their own cable for the most aprt
<azonenberg> part*
<Degi> Yeah lol
<Degi> Or maybe as a wideband load
<azonenberg> I managed to find a vendor willing to play ball
<Degi> How does it work? High dissipation dielectric? Thin center conductor?
<azonenberg> they ideally want large volume (qty 1k or so) orders but are willing to give me a handful as engineering samples for R&D
<azonenberg> So we're getting that order in progress now
<azonenberg> the prototype cables are SMPM at the probe head end and BNC at the scope end, but have no compensation box
<azonenberg> then that Crystek housing i linked is a BNC male-to-female insertable filter chassis
<azonenberg> which will contain my own compensation circuit
<azonenberg> the probe head will essentially be an AKL-PT5 with the 350 ohm body resistor swapped out for a 9M and a capacitor in parallel
<azonenberg> i haven't done the board design for it yet but it should be straightforward
<azonenberg> as far as how it works, generally speaking the inner conductor is very thin (like 39 AWG or something) nichrome
<azonenberg> and usually crinkled slightly to increase the resistivity per unit length of cable
<azonenberg> the dielectric is a foamed polymer that has a very low dielectric constant
<azonenberg> i don't think there is much in the way of dielectric loss, the idea is to be flat across a wide band so you want the loss as resistive as possible
<GenTooMan> I should update scopehal ... hmm it's been quite a while :P
<azonenberg> Lol. yeah i've been doing a lot of work on it lately