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 <jeroen@nospam.please>
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: <v44pdr$3lquc$1@dont-email.me>
References: <v426ri$2ni84$1@dont-email.me>
 <f1d96jtvb2pokgermt7fqt751ed9gpjfcn@4ax.com> <v42jgp$2gbeq$1@dont-email.me>
 <v42ju0$2gbeq$2@dont-email.me> <97s96j5fajs26f6eg9odqs48skgghoson5@4ax.com>
 <v43vk8$3dhg7$2@dont-email.me> <ntfb6jlp9g4i62rdkjv3fr692jm46u541i@4ax.com>
 <v44lvb$3kncn$2@dont-email.me>
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: <v44lvb$3kncn$2@dont-email.me>
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
>> <cd999666@notformail.com> 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
>>>> <jrwalliker@gmail.com> 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
>>>>>>> <cd999666@notformail.com> 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