Re: RF Connector Type ID

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. ;-)