Discussion:
RF Connector Type ID
(too old to reply)
Cursitor Doom
2024-06-08 18:10:59 UTC
Permalink
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
Edward Rawde
2024-06-08 18:41:23 UTC
Permalink
Post by Cursitor Doom
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
Some variant of sma?
https://www.google.com/search?q=sma+connector

smb and smc also exist.
john larkin
2024-06-08 19:43:13 UTC
Permalink
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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.
John R Walliker
2024-06-08 21:47:04 UTC
Permalink
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
John R Walliker
2024-06-08 21:54:07 UTC
Permalink
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
john larkin
2024-06-09 00:06:18 UTC
Permalink
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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.
Cursitor Doom
2024-06-09 10:19:52 UTC
Permalink
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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.
Bill Sloman
2024-06-09 13:15:44 UTC
Permalink
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
<snip>
Post by Cursitor Doom
Post by john larkin
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.
You need to manage the transition between 50R transmission line in the
cable and the 50R trace in the board. Traces buried in the board can be
non-dispersive, and you can work out how wide the trace has to be and
how far from ground planes that carry the return current to get you 50R.

A connector on the edge of the board needs special care. The pad stack
is a collection of metalised areas in the edge of the board that provide
a more-or-less seamless transition.
--
Bill Sloman, Sydney
--
This email has been checked for viruses by Norton antivirus software.
www.norton.com
john larkin
2024-06-09 15:03:18 UTC
Permalink
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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.

Loading Image...

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.

Loading Image...
Cursitor Doom
2024-06-09 16:41:15 UTC
Permalink
Post by john larkin
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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.
Loading Image...?
rlkey=nbmbyb0f54uslcpc0nh7rs21p&raw=1
Post by john larkin
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.
Loading Image...?
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. ;-)
john larkin
2024-06-09 17:25:32 UTC
Permalink
On Sun, 9 Jun 2024 16:41:15 -0000 (UTC), Cursitor Doom
Post by john larkin
Post by john larkin
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
Post by john larkin
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.
Cursitor Doom
2024-06-09 17:31:54 UTC
Permalink
Post by john larkin
On Sun, 9 Jun 2024 16:41:15 -0000 (UTC), Cursitor Doom
Post by john larkin
Post by john larkin
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
Post by john larkin
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.
john larkin
2024-06-09 21:01:58 UTC
Permalink
On Sun, 9 Jun 2024 17:31:54 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sun, 9 Jun 2024 16:41:15 -0000 (UTC), Cursitor Doom
Post by john larkin
Post by john larkin
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
Post by john larkin
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.
Jeroen Belleman
2024-06-09 17:42:52 UTC
Permalink
Post by john larkin
On Sun, 9 Jun 2024 16:41:15 -0000 (UTC), Cursitor Doom
Post by john larkin
Post by john larkin
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
Post by john larkin
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.
Yes please!

Jeroen Belleman
Jeroen Belleman
2024-06-09 17:42:19 UTC
Permalink
Post by john larkin
Post by john larkin
On Sun, 9 Jun 2024 10:19:52 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
Post by john larkin
On Sat, 8 Jun 2024 22:54:07 +0100, John R Walliker
Post by John R Walliker
Post by john larkin
On Sat, 8 Jun 2024 18:10:59 -0000 (UTC), Cursitor Doom
Post by Cursitor Doom
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
Post by john larkin
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
Gerhard Hoffmann
2024-06-09 20:38:50 UTC
Permalink
Post by john larkin
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
That giant center pad gives away the advantage that you could have
from the costly SMA connector.

<
https://www.flickr.com/photos/***@N07/51843174578/in/datetaken/ >

This is nearly as bad as the unpopulated SMA at the right end of the
line. The left SMA is one with a thick center pin. Unsuitable on this
cheap JLCPCB 4 layer board. you even see the amount of solder.

This is the next try: (4 TI LM2594/95 synthesizers + test stuctures)
<
https://www.flickr.com/photos/***@N07/51844498620/in/datetaken/ >
red = top, green = bottom, inner layers cut out.

setup on tdr refl. + transmission:
<
https://www.flickr.com/photos/***@N07/53780177186/in/dateposted-public/
result:
<
https://www.flickr.com/photos/***@N07/53780597885/in/dateposted-public/
The SMAs are at division 7 and 8. Very slightly overcompensated,
it could also mean that I need some more GND vias.

The microstrip is slightly more than 50 Ohms. JLCPCB's calculator
says 11.5 mil for 50, it took only 10 to see if I can easily escape
a BGA. The funny bends are not really punished.

The 10 cm of FR4 do not demolish the rise time. Not bad for
€1.40 per 4 layer board.

regards,
Gerhard
john larkin
2024-06-09 20:51:36 UTC
Permalink
Post by Gerhard Hoffmann
Post by john larkin
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
That giant center pad gives away the advantage that you could have
from the costly SMA connector.
That pic was the connector on a PCB that was intended for the big-pin
part. A skinny trace would be appropriate for the Mueller SMA, but in
real life the cheaper big-pin part TDRs about the same.
Post by Gerhard Hoffmann
<
This is nearly as bad as the unpopulated SMA at the right end of the
line. The left SMA is one with a thick center pin. Unsuitable on this
cheap JLCPCB 4 layer board. you even see the amount of solder.
We tweak the pad stack to compensate for the big pad. That works
pretty well.
Post by Gerhard Hoffmann
This is the next try: (4 TI LM2594/95 synthesizers + test stuctures)
<
red = top, green = bottom, inner layers cut out.
<
<
Big improvement.
Post by Gerhard Hoffmann
The SMAs are at division 7 and 8. Very slightly overcompensated,
it could also mean that I need some more GND vias.
The microstrip is slightly more than 50 Ohms. JLCPCB's calculator
says 11.5 mil for 50, it took only 10 to see if I can easily escape
a BGA. The funny bends are not really punished.
The 10 cm of FR4 do not demolish the rise time. Not bad for
€1.40 per 4 layer board.
Short traces on cheap boards are pretty good.
Post by Gerhard Hoffmann
regards,
Gerhard
Cursitor Doom
2024-06-09 17:26:23 UTC
Permalink
Gentlemen,

The previous one I queried was indeed an SMB; many thanks to those who
correctly identified it.
Now, does anyone know anything about these ones? Ignore the N-type part of
it, I'm referring to the rest of the item in the photo. They too are 50
ohm and snap-on; very much like SMB but much smaller.
Any insight would be most welcome.

https://disk.yandex.com/i/8ZJgAkD-ps5sQQ
Phil Hobbs
2024-06-09 18:16:41 UTC
Permalink
Post by Cursitor Doom
Gentlemen,
The previous one I queried was indeed an SMB; many thanks to those who
correctly identified it.
Now, does anyone know anything about these ones? Ignore the N-type part of
it, I'm referring to the rest of the item in the photo. They too are 50
ohm and snap-on; very much like SMB but much smaller.
Any insight would be most welcome.
https://disk.yandex.com/i/8ZJgAkD-ps5sQQ
U.FL.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Cursitor Doom
2024-06-09 23:15:00 UTC
Permalink
Post by Phil Hobbs
Post by Cursitor Doom
Gentlemen,
The previous one I queried was indeed an SMB; many thanks to those who
correctly identified it.
Now, does anyone know anything about these ones? Ignore the N-type part
of it, I'm referring to the rest of the item in the photo. They too are
50 ohm and snap-on; very much like SMB but much smaller.
Any insight would be most welcome.
https://disk.yandex.com/i/8ZJgAkD-ps5sQQ
U.FL.
Cheers
Phil Hobbs
Aha! Thanks, Phil.

Loading...