Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sun, 09 Jun 2024 17:25:33 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: RF Connector Type ID Date: Sun, 09 Jun 2024 10:25:32 -0700 Message-ID: <8kob6j1igv9nf27s9jp75cijdslie6e68h@4ax.com> References: <97s96j5fajs26f6eg9odqs48skgghoson5@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 106 X-Trace: sv3-u7gMmnFYXB/a7ym51tyO1Pm7Gubj86nhxzudWnc3bhZXULk3GMS0oV1PEj3x5qq3+cBUr1Nh8FP+Eb0!KPVEfW9AUGE/xTvsBC2qwaQTY4bAUsNoZ3/DzPZ3Xo7o6bjLpTw825KEIXSARe5Ey59W7PQmfmA5!2ozVuQ== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 5423 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.