BNC centre pin size for 75 and 50 ohm sockets

[Fred]

I have access to some 50 ohm BNC sockets. However it must mate to a 75 ohm
plug. Since we are talking about video frequencies here I'm not worried
about mismatches etc.

What are the dimensional differences between the 50 and 75 ohm sockets?

Can anyone point to dimensioned drawings of both types including pin size
etc?

 

[Matt North]

I have access to some 50 ohm BNC sockets. However it must mate to a 75 ohm
plug. Since we are talking about video frequencies here I'm not worried
about mismatches etc.

What are the dimensional differences between the 50 and 75 ohm sockets?

Can anyone point to dimensioned drawings of both types including pin size
etc?

Try lookind at data sheets for both types at www.farnell.co.uk

 

[John Woodgate]

I have access to some 50 ohm BNC sockets. However it must mate to a 75 ohm
plug. Since we are talking about video frequencies here I'm not worried
about mismatches etc.

What are the dimensional differences between the 50 and 75 ohm sockets?

Can anyone point to dimensioned drawings of both types including pin size
etc?

We had a long (and at times misleading) thread on this a while back. The
metal parts are identical. The 50 ohm connectors have additional
'insulation' members, which are actually dielectric to increase the
shunt capacitance and thus lower Zo from 75 to 50 ohms.

In the distant past, there were variations. The current standard is IEC
60169-8.

 

[Per-Åke Andersson]

I have access to some 50 ohm BNC sockets. However it must mate to a 75 ohm
plug. Since we are talking about video frequencies here I'm not worried
about mismatches etc.

What are the dimensional differences between the 50 and 75 ohm sockets?

Can anyone point to dimensioned drawings of both types including pin size
etc?

For example:

http://www.tycoelectronics.com/products.stm
http://www.hubersuhner.com

/Per-Ake

 

[Roger Gt]

: I read in sci.electronics.design that Fred <[email protected]>
wrote (in
: <[email protected]>) about 'BNC centre pin
size for
: 75 and 50 ohm sockets', on Wed, 11 Aug 2004:
: >I have access to some 50 ohm BNC sockets. However it must mate
to a 75 ohm
: >plug. Since we are talking about video frequencies here I'm
not worried
: >about mismatches etc.
: >
: >What are the dimensional differences between the 50 and 75 ohm
sockets?
: >
: >Can anyone point to dimensioned drawings of both types
including pin size
: >etc?
: >
: >
: We had a long (and at times misleading) thread on this a while
back. The
: metal parts are identical. The 50 ohm connectors have additional
: 'insulation' members, which are actually dielectric to increase
the
: shunt capacitance and thus lower Zo from 75 to 50 ohms.
:
: In the distant past, there were variations. The current
standard is IEC
: 60169-8.
: --
: Regards, John Woodgate, OOO - Own Opinions Only.


An example of BAD information! The intrinsic impedance is a
function of the diameter of the conductor and its separation from
the barrel. the dielectric constant for the insulator is
considered, just as it is for any separator, but it is only one
factor.

Roger Gt.

 

[Helmut Sennewald]

I have access to some 50 ohm BNC sockets. However it must mate to a 75 ohm
plug. Since we are talking about video frequencies here I'm not worried
about mismatches etc.

What are the dimensional differences between the 50 and 75 ohm sockets?

Can anyone point to dimensioned drawings of both types including pin size
etc?

Hello Fred,
I tried with Google: bnc 75 50 difference

The first hit.
http://www.levitonvoicedata.com/support/technotes/tech_note_detail.asp?tnID=175

Original text from this page follows.

--- begin ---

Difference between 50 Ohm and 75 Ohm BNC Connectors

What are the physical differences between 50 Ohm BNC connectors and 75 Ohm
BNC connectors?
There are a few physical differences. The 75 Ohm plug’s center pin has the
same diameter in the rear as in the front mating interface area. Whereas,
the 50 Ohm plug’s center pin has a thicker diameter in the rear area where
it is crimped.

Both plugs have the same pin size in the mating area. Regarding the
dielectric on each, the 75 Ohm connector’s dielectric is made of Teflon
which has higher impedance properties than Delrin. The 50 Ohm connector’s
dielectric is made of Delrin.

Finally, the main physical difference is that the 75 Ohm plug does not have
extended dielectric around its outer spring fingers.

--- end ---

Hope that helps,

Best regards,

Helmut

 

[Reg Edwards]

If the BNC plugs and sockets in question, and indeed other types of
connectors, are to be used only at a few hundred MHz and below, then the
user should be aware that a 75/50 ohm mismatch over a distance considerably
less than the length of a connector will cause absolutely negligible
measuring errors in such matters as SWR.

Start worrying only when there is a large energy content in the signal above
1 GHz.

It is necessary only to ensure a good, solid, electrical contact in
connectors at DC and the HF properties will look after themselves.

Mechanically wobbling, intermittent, connectors are the only menace but this
applies at all frequencies.

It is only 50/75 ohm cable mismatch impedances over distances which are
appreciable fractions of a 1/4-wavelength which matter at HF and VHF. And
even then not very much.

There's often little cause for any loss of sleep. But most people, amateurs
and professionals alike, suffer unnecessarily from delusions of measurement
accuracy.

It's always 10 times worse than imagined.

I'll try not to mention this ever again.

 

[John Woodgate]

I read in sci.electronics.design that Reg Edwards
et.com>) about 'BNC centre pin size for 75 and 50 ohm sockets', on Wed,
11 Aug 2004:

It is necessary only to ensure a good, solid, electrical contact in
connectors at DC and the HF properties will look after themselves.

This is the point, Reg. If, as seems likely at first sight (and was so a
long time ago), the centre pins of the 50 and 75 ohms connectors were of
different diameters, either the connectors won't mate or the '75 ohm'
pin will not make good contact with the '50 ohm' sleeve.

 

[Reg Edwards]

To summarise what I have said earlier in general about 50/75 connectors -

If the dimensions of pins of mixed 50/75 ohm connectors allow good, solid,
DC connections then there's nothing whatever to worry about. The HF
properties and performance of single mixed plugs and sockets up to and
including VHF will look after themselves quite satisfactorily.

There's far too much importance attached to actual impedances below 1 Ghz.

I am unfamiliar with the actual specified dimensions of 75 and 50 ohm pins
and sockets. I leave it to others to confirm that a satisfactory DC
connection is obtainable. If it is then the situation is quite clear. Stop
worrying about things which don't matter.

If it isn't then you've got problems at all frequencies.

 

[Roger Gt]

: I read in sci.electronics.design that Roger Gt <[email protected]>
wrote (in
: <[email protected]>) about 'BNC
centre pin
: size for 75 and 50 ohm sockets', on Wed, 11 Aug 2004:
:
: >An example of BAD information! The intrinsic impedance is a
function of
: >the diameter of the conductor and its separation from the
barrel. the
: >dielectric constant for the insulator is considered, just as it
is for
: >any separator, but it is only one factor.
:
: No, Roger. You know not of what you speak. I've posted the Zo
equation
: here two of three times recently. The capacitance between the
conductors
: directly influences the value.


You sure Think you know it all, don't you?

But you didn't understand what I said.....

 

[David Lesher]

We had a long (and at times misleading) thread on this a while back. The
metal parts are identical. The 50 ohm connectors have additional
'insulation' members, which are actually dielectric to increase the
shunt capacitance and thus lower Zo from 75 to 50 ohms.

I can say with hard experience that in N connectors; the center
pins are different sizes...

Yea, it was a ^&%&^ Oh Shit....

 

[Glenn Gundlach]

To summarise what I have said earlier in general about 50/75 connectors -

If the dimensions of pins of mixed 50/75 ohm connectors allow good, solid,
DC connections then there's nothing whatever to worry about. The HF
properties and performance of single mixed plugs and sockets up to and
including VHF will look after themselves quite satisfactorily.

There's far too much importance attached to actual impedances below 1 Ghz.

I am unfamiliar with the actual specified dimensions of 75 and 50 ohm pins
and sockets. I leave it to others to confirm that a satisfactory DC
connection is obtainable. If it is then the situation is quite clear. Stop
worrying about things which don't matter.

If it isn't then you've got problems at all frequencies.

The 50/75 issue is important in standard definition serial digital
video running at 270 mbits (ccir 601). The impedance variations cause
the serial receivers to lose lock. Granted, it takes more than 1
connector to mess things up. The typical path at our plant through
routers and patch panels has at least 8 connectors for a simple
machine to machine dub. Double it for a standards conversion
(PAL-NTSC).
GG

 

[Ian Stirling]

I read in sci.electronics.design that Reg Edwards
et.com>) about 'BNC centre pin size for 75 and 50 ohm sockets', on Wed,
11 Aug 2004:


This is the point, Reg. If, as seems likely at first sight (and was so a
long time ago), the centre pins of the 50 and 75 ohms connectors were of
different diameters, either the connectors won't mate or the '75 ohm'
pin will not make good contact with the '50 ohm' sleeve.

Isn't it irrelevant.
Sureley the impedance is between the outer shell of the sleeve, and the
inside of the socket barrel?

 

[Fred]

For example:

http://www.tycoelectronics.com/products.stm

Couldn't find any BNCs directly here.

http://www.hubersuhner.com

Does say that 50 and 75R connectors are intermateable. There are also
dimenasioned drawings on this website. Many thanks.

 

[Fred]

I have access to some 50 ohm BNC sockets. However it must mate to a 75 ohm
plug. Since we are talking about video frequencies here I'm not worried
about mismatches etc.

What are the dimensional differences between the 50 and 75 ohm sockets?

Can anyone point to dimensioned drawings of both types including pin size
etc?

Many thanks for all those who responded to my post. Thanks to Per-Åke I
have a drawing which indicate the mechanical differences. Also thanks to
Helmut I am also aware of the dielectric differences.