BNC centre pin size for 75 and 50 ohm sockets

ohm

Try lookind at data sheets for both types at

I read in sci.electronics.design that Fred wrote (in ) about 'BNC centre pin size for

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

For example:

/Per-Ake

: >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.

I read in sci.electronics.design that Roger Gt wrote (in ) about 'BNC centre pin size for 75 and 50 ohm sockets', on Wed, 11 Aug 2004:

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.

"Fred" schrieb im Newsbeitrag news:4119d8e2$0$206$ snipped-for-privacy@news.zen.co.uk...

ohm

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

The first hit.

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

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

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.

I read in sci.electronics.design that Reg Edwards wrote (in ) about 'BNC centre pin size for 75 and 50 ohm sockets', on Wed,

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.

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.

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

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

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

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

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

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

ohm

size

Couldn't find any BNCs directly here.

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

ohm

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.