Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Jeroen Belleman Newsgroups: sci.electronics.design Subject: Re: RF Connector Type ID Date: Sun, 9 Jun 2024 19:42:19 +0200 Organization: A noiseless patient Spider Lines: 97 Message-ID: References: <97s96j5fajs26f6eg9odqs48skgghoson5@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sun, 09 Jun 2024 19:40:12 +0200 (CEST) Injection-Info: dont-email.me; posting-host="4d5bb2651e497ec06f1079f3dcd2e601"; logging-data="3861452"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19VRn+kfbxXYcb4qRYQvuMl" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Cancel-Lock: sha1:0HQLpdTSg542woaCi1zzz53V/9Q= In-Reply-To: Content-Language: en-US Bytes: 5200 On 6/9/24 18:41, 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. ;-) RF gets more understandable when you realize that electrical signals really propagate as electromagnetic fields *between* conductors, rather than as currents and voltages. Jeroen Belleman