Path: ...!feed.opticnetworks.net!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 17:31:54 -0000 (UTC) Organization: A noiseless patient Spider Lines: 112 Message-ID: References: <97s96j5fajs26f6eg9odqs48skgghoson5@4ax.com> <8kob6j1igv9nf27s9jp75cijdslie6e68h@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 09 Jun 2024 19:31:54 +0200 (CEST) Injection-Info: dont-email.me; posting-host="d4ac345ff05c2404d7e3496200634bde"; logging-data="3825047"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+zGom1mOQ9E2EfoLA3trX22GpbbKwPM2Y=" User-Agent: Pan/0.149 (Bellevue; 4c157ba) Cancel-Lock: sha1:l8Hw5kodNMnUUqt9lNXS2prBa54= Bytes: 5737 On Sun, 09 Jun 2024 10:25:32 -0700, john larkin wrote: > On Sun, 9 Jun 2024 16:41:15 -0000 (UTC), Cursitor Doom > wrote: > >>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. ;-) > > We do picosecond time-domain stuff, which resembles RF except that is > broadband, all the way down to DC, so we can't tweak to tune things into > some narrow RF band. > > I expect that it's impossible to do really fast stuff, 30 GHz-ish, with > parts soldered to FR4 PC boards. > > I just disassembled a National Instruments PXIe RF module (with great > difficulty) and it's really bizarre. And it's only 6 GHz! > > I might post some pics. Please do! I struggle with parasitics at even modest frequencies so it's always fascinating to see how the pros overcome these barriers.