Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Cursitor Doom Newsgroups: sci.electronics.design Subject: Re: RF Connector Type ID Date: Sun, 9 Jun 2024 16:41:15 -0000 (UTC) Organization: A noiseless patient Spider Lines: 90 Message-ID: References: <97s96j5fajs26f6eg9odqs48skgghoson5@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 09 Jun 2024 18:41:16 +0200 (CEST) Injection-Info: dont-email.me; posting-host="d4ac345ff05c2404d7e3496200634bde"; logging-data="3825047"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/yZ7BNuPKRsBNPPjHhKH3YMbTQ1IeePWw=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:zad0Z8CyC5z/asIRmbR1BTadD78= Bytes: 4688 On Sun, 09 Jun 2024 08:03:18 -0700, john larkin wrote: > On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom > wrote: > >>On Sat, 08 Jun 2024 17:06:18 -0700, john larkin wrote: >> >>> On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker >>> wrote: >>> >>>>On 08/06/2024 22:47, John R Walliker wrote: >>>>> On 08/06/2024 20:43, john larkin wrote: >>>>>> On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom >>>>>> wrote: >>>>>> >>>>>>> Gentlemen, >>>>>>> >>>>>>> Can anyone identify these connectors? HP use 'em an awful lot for >>>>>>> interconnecting the boards of their analyzers to route 50 ohm RF >>>>>>> signals around the various inside sections. >>>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>> CD. >>>>>>> >>>>>>> https://disk.yandex.com/i/LQ1ytGUQCf7OTw >>>>>> >>>>>> Probably SMBs. >>>>> >>>>> +1 >>>>> >>>>> John >>>>> >>>>Most of the connectors in the image look like SMB which is a "click >>>>on" >>>>push fit connector and is cylindrical at the end. A few which have a >>>>hex profile at the end may be SMC which is a threaded connector. >>>>SMA is threaded and a bit larger, but has the best high frequency >>>>performance of them all. >>>> >>>>John >>> >>> We like SMBs because that are quick to mate and un-mate without tools, >>> so can be mounted very close together. They work fine to 6 or 8 GHz, >>> about what you can do with discretes on FR4. >>> >>> Shining Star makes nice cheap edge-launch SMAs and SMBs. A proper pad >>> stack keeps things 50 ohms. >> >>Could you possibly expand on that last sentence, please? I've never >>encountered a 'pad stack' before. > > A PCB's pad stack is a diagram of the number of conductive and > insulating layers and their thickesses and composition. It must be > specified when you buy a board. > > Sometimes you get to choose between a few canned stacks, and sometimes > you diagram your own. > > We mostly do 4 and 6-layer boards, with some 2-layer and the occasional > 8 or even 10 copper layers. Never single layer. > > Our boards are mostly 0.062" thick, and I like layer 2 to be a solid > ground plane. Some internal layers are power planes. If you solder an > edge-launch SMA or SMB connector to layer 1, the layer 2 ground plane is > too close to the center pin of the connector, so that bit of the signal > path is too low impedance. So one does creative shaped cutouts in the > various layers to keep the impedance uniform and the reflections down. > We did e-m simulations (with ATLC) and test boards to get that right. > > The cheaper connectors have a giant round center pin, which requires > attention. > > https://www.dropbox.com/scl/fi/vfi56wy5hkwva51bx77z6/SS_SMA_Edge.JPG? rlkey=nbmbyb0f54uslcpc0nh7rs21p&raw=1 > > That pin is around 100 ohms in free space! > > There are more expensive conectors with a tiny flat pin that > theoretically matches a layer 1 trace width directly, but I haven't > found them to be worth it on FR4 boards and 30 ps edges. > > https://www.dropbox.com/scl/fi/rptmh5f4umscqqpegatw6/Mueller_SMA.JPG? rlkey=1eonuljqekvrszyb9tce5s1hr&raw=1 Thanks, John; I'm somewhat less ignorant now than I was! Seriously though, it's clear the reason I've not encountered these is due to the fact I just experiment with single layer boards which don't need them, from what you implicitly state. Life must get really "interesting" with RF in multi-layer boards. ;-)