[FS] [USA] Z0 resistive probes

[electrolust]

I have quite the collection of Z0 resistive probes. I've no idea why I've been collecting them, but now it's time to divest myself of them.

It's too bad I only now, while googling to write this ad, learned of the AKL-PT1 DIY probe.

https://hackaday.com/2020/05/07/open-source-2-ghz-oscilloscope-probe/
https://www.kickstarter.com/projects/azonenberg/akl-pt1-2-ghz-passive-oscilloscope-probe/description
https://github.com/azonenberg/starshipraider/tree/master/boards/probes/handheld-resistive-probe

Looks like he had 100 PCBs made for 25 backers. Who knows if he made all 100 PCBs into probes though. The store they sell through (Elegant Invention) is shut. So either way, it looks like you can't buy this now. At $250, I'm not entirely sure they are worth it. You can get a 10020A set for less than that. So had I known about it in advance perhaps I would have passed regardless.

Enough! You know what a resistive probe is. I think I have every commercially made one. I am nearly certain I have enough qty to satisfy demand. These things just aren't in demand. Most people that can afford a high bandwidth scope can probably afford an active FET probe, which is more versatile.

Higher offers will get the better quality / more complete kits. PM me and let me know what model you want and an offer price. I'll collect offers for a bit then send them out all at once. Paypal or Apple Pay are accepted. Cash as well, if you don't mind sending it through the mail. I can do international shipping if you want to pay the ebay global fees on top, otherwise USA only.

I won't post the pictures here, because the sets are in different states of accessory contents. You can find representative pictures online. I will send you the pictures of the actual set you are buying for your approval before completing the sale. Most of my sets are in quite good condition, and quite complete. I will mix and match accessories to build complete sets in the highly likely case that the sales aren't fully subscribed.

You can find current asking prices on ebay and offer much lower than that. Those sets literally never sell at those prices. The $250 for 2GHz (900fF) for a DIY set with a very long rigid probe body, vs $??? for a used commercial 6+GHz (100fF) set with very small "operating area" (basically just a probe tip immediately terminating into a cable), vs current ebay asking prices, should give you a guide on what to offer.

I've attached the user manuals for the various kits to this post. Below are the list prices when new. I think the Lecroy is the only one still sold new.

Each kit has its own unique advantages and disadvantages in their use. Besides the obvious performance difference, there are ergonomic differences. Not bad or good, they are just all different from each other. Unlike your standard passive probe, which are all alike.

HP 10020A ($100 in 1978 dollars == $746.89 in 2020 dollars). This is a fun probe because it contains many ratios, including 1:1. But the performance is the worst -- they aren't even rated! Tip capacitance is 700fF, so you do the math. per HP, "Effect on risetime of a 100-MHz system is negligible". The probe tips screw on to the handle and contain the resistor. The tips have a .25"-ish dia metal body, stainless I think. I had one set that was moderately corroded, a bunch of normal use looking sets, and then later I got a set that looked absolutely brand new. It inspired me to polish the grime off of the worst set. It came out sparkling and while I don't have a 2GHz scope to test the performance, it seems ok after the procedure. Anyway, these are made in the old fashioned way, to last. I have very many of these, so I suggest "ordering" 2 sets ... Otherwise the price will be so cheap as to hardly be worth my while.

Tektronix P6150 ($1860). Interesting ground clips for these.  Also these are the most interesting probe tips as there is a PCB adapter (I have many) that you solder on as a test point. It holds the probe tip rigidly. None of the others have that feature or even capability, so for the others you have to setup a separate fixture for non-momentary probing, like you might do for any modern passive probe.

HP/Agilent 54006A ($3400). These are built around a specific Caddock resistor, made just for Agilent. I have a lot of these, but also many missing parts. You never see these for sale with a full complement of resistors. At one point the connector design changed. The new style is more attractive to look at but I doubt there's any performance difference -- seeing as how the model# didn't change. Probably a supplier change (old connector no longer available) as opposed to an intentional design change. Some of these are branded HP and some Agilent. There's not a consistent change in apparent quality or age across the 2 different brandings. Also I may have mixed the parts up across sets anyway. But if you want a case that is branded one way or the other, specify that.

Lecroy PP066 ($1600). This one is rated to the highest frequency, 7.5GHz. It's the same design as the 54006A physically, but with
a different resistor -- HDK apparently. I've attached a photo of them because you won't find it online. As well, it's very beautifully made. The package is some kind of epoxy. The back side is symmetrical to the front, ie the main body is flat. It suggests a stripline, although I don't see how that can be the case. The photo gridlines are 5mm square. I only have one of these sets, and I would want a lot to part with it.

If you even got through this post, expect to wait some time for me to collect all the orders (if any!) before I fulfill them. I want to get rid of these, not maintain a museum, so offer accordingly.

[electrolust]

BTW, first mention I can find of the 10020A is in the Nov 1968 HP Journal. Clearly it existed before then. I think the mention of it is to compare vs their new active probe, the 1123A? The article doesn't mention the 10020A at all, it just refers to it in the 1123A specs. Which is good only to 220 MHz!! For an active probe! But it has high input impedance, vs the 10020A.

Just look at those "miniature" components!

Probably designed with pencil and paper in those days?

[azonenberg]

Hi, I'm the designer of the AKL-PT1. Thought I'd chime in with a few notes. First off, I made 100 boards but only populated 19 of them. 17 went to backers and I kept 2 for myself. Another 20ish were sold as the "bare board for DIY assembly" option, and I still have the others. I'm not in a hurry to sell any of the other boards (or my two assembled probes) but would consider an offer if someone was interested.

The reason for the price isn't the probe body or me taking a huge profit, it's the high cost of accessories from PMK. The tips are $31 for 5, the ground leaf is $40 each. The Z-ground is $35 for 5 and the flex ground is a whopping $28. The bipod holder included in the pro package is is $45. Oh, and then throw in $300 of shipping for each accessory order no matter how small! It's a total ripoff, but I haven't found a cheaper way to get/make these parts yet. Unfortunately tip sockets and various ground accessories are necessary if you want to make a handheld "browser" type probe.

I'm not openly selling the AKL-PT1 anymore because I discovered how much room the design had for improvement. While the v1.0 edition on the Kickstarter does meet the advertised specs, it's not nearly as good as it could be and selling it when I did was a mistake. The latest v1.2 prototype is $6 cheaper thanks to some BOM changes and pushes the -3 dB bandwidth to around 5.25 GHz, as well as significantly lowering the tip capacitance and shifting a resonance up about 2 GHz. v1.3 is at OSHPark now and, fingers crossed, will be even better. I intend to reopen sales once I honestly believe I've pushed it as far as I can. Price will be about the same as on the Kickstarter although I may have to increase the student edition pricing slightly - it was intended to be sold at break-even but the $125 price ended up being a small net loss.

My goal for the AKL-PT1 is to be competitive with the PicoConnect 900 series (https://www.picotech.com/accessories/gigabit-digital-passive-test-probes, which you didn't mention in your post - they're the other big transmission line probe I know of on the market) at roughly a quarter of the price, or half Pico's price if you want the full characterization report with individually serialized S-parameters etc.

I'm also working on two additional transmission line probes, which use the same circuit as the AKL-PT1 but in different form factors. These are solder-in designs, which work better when you have a lot of test points on a board (no worries about jiggling a probe out of place) and don't need any of the expensive PMK parts so I can sell them much cheaper. First-round prototypes of both are currently at OSHPark and the schematics and layout are on my GitHub. Targeting 5 GHz bandwidth for both versions.

The AKL-PT2 is a flex PCB with a protective TPU strain relief around part of it, then a SMA connection to the scope. The board is $26 for 3 at OSHPark (although you have to add a FR4 stiffener yourself as OSHPark doesn't do these) and will be a lot less in volume from China. The SMA is around $10, the resistors total about $6, and the 3D printed strain relief is $15 at Shapeways. Hoping to be able to sell these for $50ish.



The AKL-PT3 is an ultra-miniaturized probe (currently 9.9 x 5.5 mm and I can probably shrink that) for dense boards that trades connector lifetime for minimal size. It's $2 for 6 at OSHPark, much less in volume, plus a $0.50 U.FL connector and $6 of resistors. Targeting $10-15 retail price.



Also, very interesting to see the PP066 resistors! I wonder if they're using carbon or nichrome film printed on an alumina substrate to avoid the parasitic capacitance you get from the end caps of typical SMT resistors? I assumed they were using the same Caddock parts everyone else was.

EDIT: The other transmission line probe I'm aware of the the $319 Pico TA061 (https://www.tequipment.net/Pico/TA061/Passive-Oscilloscope-Probes/#description). It's a rebranded PMK PML-751 probe (PMK order number 875-751-000) and is absolute garbage, worse than the AKL-PT1 and almost certainly every other probe on your list. It has a massive resonance at 900 MHz which causes about 2 dB of peaking on the S21 curve and a huge notch effect, -15 dB of return loss across an open circuit rather than the -2 dB you'd expect from an ideal resistive probe. It also has only 1.5 GHz of advertised bandwidth, although my VNA says it's more like 1.2, and a very steep rolloff after that.

EDIT 2: Also, active FET probes are not actually universally better. Starting at 575 MHz, the LeCroy ZS1500 (only active probe I have in my lab right now) actually has worse return loss/higher loading than most of the transmission line probes I've tested. At the 1.5 GHz rated bandwidth the PicoConnect 921 has -2.14 dB S11 and the ZS1500 is -5.88.

[electrolust]

Hi, I'm the designer of the AKL-PT1.

Yay! Glad you found this. Thanks for the PT1, it looks like it was a fun project. The part I like the best is the hackaday picture, where we can see the test coupon still attached.

The reason for the price isn't the probe body or me taking a huge profit,

I hope I wasn't implying that. I think (I like to think) that folks here understand the cost that goes into making ... anything. It's 100% clear, to me at least, that you would have lost money on this project even if it were fully subscribed. Low volume means no NRE recovery and high expense ratio. Kickstarter's 10% doesn't help either. Even if you think you broke even, I'm sure it's only because you haven't valued your time properly. That said, it's nice that people go into these projects without thinking about profit. It's more about sharing something, which is great.

And as you point out, if you're not vertically integrated the supplier costs are enormous.

I suppose your price is actually good, considering that used commercial probes at "correct" prices aren't available on a whim. I have collected all my probes over years, without a specific need or specific timeframe in mind. So it wasn't fair of me to criticize the value of your offering, at least in the context of the time it was offered and vs what else would have been available.

I also didn't want to step all over your project but it seemed like it was done and done, so it was a good point of reference for my own pricing.

My goal for the AKL-PT1 is to be competitive with the PicoConnect 900 series (https://www.picotech.com/accessories/gigabit-digital-passive-test-probes, which you didn't mention in your post - they're the other big transmission line probe I know of on the market) at roughly a quarter of the price, or half Pico's price if you want the full characterization report with individually serialized S-parameters etc.

Thanks for the reference. I am aware of many of picotech's products but somehow wasn't aware of this probe. I see it has solder-in test points, cool. Interesting cable that they supply with the kit as well. $1400 and you can select the ratio as well as AC vs DC coupling, I dunno seems like ok enough (commercial) pricing to me. Obviously the BOM for such a thing is minimal, but the costs are more than just the BOM. They have a company to run. If you can compete with that product, you are in good company.

BTW, Your link got munged by the forum, it's https://www.picotech.com/accessories/gigabit-digital-passive-test-probes .

The AKL-PT3 is an ultra-miniaturized probe (currently 9.9 x 5.5 mm and I can probably shrink that) for dense boards that trades connector lifetime for minimal size. It's $2 for 6 at OSHPark, much less in volume, plus a $0.50 U.FL connector and $6 of resistors. Targeting $10-15 retail price.

Nice. Since you mention picotech, let me point out https://www.picotech.com/accessories/probe-positioning-system . They are overstating the problem (there are many, reasonable enough, probe holding solutions), which I hate. But I like the product.

The original designer and creator of this product, and clearly the OEM for picotech, is https://sensepeek.com/pcbite_20 . (Super fantastic PCB workholding BTW, not even considering the probing.) The PCBite probes can hold any probe -- the probe tips of the version I have (SP10) are just a board with 2 square pins that you attach your whatever probe to via commonly available test lead adapter, whereas the picotech holds the probe directly. I see that sensepeek now has another version (SP100, SP200) which is an integrated probe head. Only €40 for the 100Mhz and €50 for the 200Mhz probes -- not bad. One could probably build a DIY 500MHz probe to suit their probe holding fixture. Maybe sensepeek don't do it themselves so as not to compete with picotech.

Maybe you could design the PT3 to mount to the PCBite snake arms? It would cost little-to-nothing and would add a great feature.

EDIT: The other transmission line probe I'm aware of the the $319 Pico TA061 (https://www.tequipment.net/Pico/TA061/Passive-Oscilloscope-Probes/#description). It's a rebranded PMK PML-751 probe (PMK order number 875-751-000) and is absolute garbage, worse than the AKL-PT1 and almost certainly every other probe on your list. It has a massive resonance at 900 MHz which causes about 2 dB of peaking on the S21 curve and a huge notch effect, -15 dB of return loss across an open circuit rather than the -2 dB you'd expect from an ideal resistive probe. It also has only 1.5 GHz of advertised bandwidth, although my VNA says it's more like 1.2, and a very steep rolloff after that.

Yeah at that size of company you don't have much vertical integration, so your accessories are all going to be rebrands. With healthy markups.

[azonenberg]

Yeah I wasn't valuing my time on the project at all. If I was billing myself at $150/hr for R&D I'd need to sell them for Keysight-level prices to recoup my expenses, and that's before you factor in the several thousand dollars I spent on Sonnet field solver licensing which I also use for other projects. But this is something I'm doing for fun and to contribute for the community, so if I sell stuff my goal isn't to turn a profit, it's to cover the cost of my consumables so I can move on to another project without spending myself into too deep of a hole.

As far as I know the PicoConnect probes are an in-house Pico design - at least I haven't found the same design sold anywhere else - but all of their other probes and accessories are obvious rebrands. The passive probes are PMK products, the sensepeek thing was obvious. Their current probes are I believe Yokogawa? and the active probes are PMK Tetris, also known as the LeCroy ZS1000/1500/2500/4000 family (although the LeCroy version has a ProBus interface with integrated power supply, it's the same probe head but not quite the same as sold by Pico/PMK directly).

From what I've seen at least one of sensepeek's products, I forget the model number, has screw-mounted probe heads that use a MMCX connector with coax to the scope. That is probably compatible with a very nice high bandwidth transmission line probe head, I've looked into designing a new probe for it but havent had the time to do serious engineering. Several GHz bandwidth is likely achievable.

It would probably be designated AKL-PT4 and be essentially the business end of a PT1 but with a MMCX jack instead of a SMA and a much shorter body, plus a mounting hole for the sensepeek arms.

I have plans to design an active differential probe at some point too, but that's a long ways out. Too many other projects...