Re: User Experience of Sampling Scopes

Jim Ford

Makes sense, Tom. I read somewhere, I think it was an article by somebody working for W.L. Gore, that the 3.5 mm connector was actually designed for test equipment like VNAs where many mating cycles were expected. As opposed to the SMA, which was designed to be cheap and reasonably high performance. SMA is only rated for something like 100 mating cycles, maybe less, while the 3.5 mm is rated for 2000 cycles.
Interesting because you'd think the 3.5 mm ones would be more fragile because of the longer unsupported pins in air dielectric.

I guess the female ones are, and extended male center pins can damage them. Yes, I need to get a connector gauge someday. Not so much need for it in my garage lab these days, though, as the only 3.5 mm connector I have is the male on my HP 5343A 26.5 GHz frequency counter. Most of the time I have an SMA bullet threaded into it anyway for ease of connecting SMA males on test cables.

I did get Raytheon to buy a set of Mini-Circuits SMA female to 3.5 mm male adaptors to use as connector savers on the ENA. IIRC, they were about $60 apiece, as opposed to rip-off Pasternack, who wanted $180!
Fortunately our cables seemed to be fine, at least up to 9 GHz where the ENA tops out.

Jim Ford

------ Original Message ------
From: "Tom Lee" <>
Sent: 1/31/2021 2:07:27 PM
Subject: Re: [TekScopes] User Experience of Sampling Scopes

Thanks for being “that guy”. Not being aware of the difference can cause expensive damage, and it’s one of my pet peeves.

The two connectors can mate, but the 3.5mm connector is made to much tighter tolerances. It also has an air dielectric. Mating to a poorly made (or badly abused) SMA can wreck a 3.5mm connector’s ability to maintain low SWR all the way out to its TEM limit. Permanent damage can be done by a single connect-disconnect cycle.

I have sacrificial connector savers on all of my expensive gear, but occasionally a student will remove them — against the rules — to shorten a path or because they think the savers are introducing some artifacts. If they then connect a random SMA cable to the gear, those students have their lab access cards deactivated pretty quickly.


Sent from my iThing, so please forgive typos and brevity.

On Jan 31, 2021, at 1:42 PM, snapdiode via <> wrote:

Well, not to be "that guy", but the SD-24 uses 3.5mm connectors... Compatible with SMA but not the same.

And I would just like to add that I have a S-52 which makes me *almost* as cool.

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