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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: RF Connector Type ID
Date: Sun, 09 Jun 2024 14:01:58 -0700
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On Sun, 9 Jun 2024 17:31:54 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:

>On Sun, 09 Jun 2024 10:25:32 -0700, john larkin wrote:
>
>> On Sun, 9 Jun 2024 16:41:15 -0000 (UTC), Cursitor Doom
>> <cd999666@notformail.com> 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. ;-)
>> 
>> 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.

Here it is:

https://www.dropbox.com/scl/fo/xalh98wfmk5b1m8renaj1/ALK2Mu87IZDBbBtyfa4Sid4?rlkey=u6ymtjdgzp9gl9pkwfw8754p3&dl=0

The RF PCBs feel like ceramic to me. The top layer whitish stuff is
conductive.

As noted, this is bizarre. And obviously very expensive to build.
What's with those machined cover plates?

But cheap on ebay! Maybe nobody wants this.