[UKMonitor]

On Jun 7, 7:54*am, Owen Duffy wrote:
Jeff Liebermann wrote :

I like Thomas and Betts Snap-n-Seal connectors:

These are known generically as "compression connectors", and I
recommended the BNC type earlier, because when used with either a BNC-F
on the antenna, or a BNC/N adapter to an N-F they are waterproof, and
neither depends critically on the retaining nut torque for good
electrical connection (as do UHF, SMA and F connectors). Compression
connectors do not use a normal hex crimp tool, but a tool unique to
themselves, and in the rest of the world, the tools are pretty
inexpensive (US20).

Whilst I say they are waterproof, with force, it is possible to break the
front of the connector out of the connector body in the types that I have
tested.

If you use ordinary (ie non waterproof) crimp BNCs, you need to figure
some way to waterproof the cable jacket to the connector body. Most do
not lend themselves to glue lined heatshrink for this purpose. Of course,
you could always treat them like UHF series, and wrap the entire joint.

Owen

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.

If you plugged a 50 Ohm plug into a 75 Ohm socket the larger centre
pin would splay out the female centre connector, so when you plugged a
75 Ohm back in again it wouldn't make contact. It used to be fairly
common practice to paint the body of the connector purple or green in
order to quickly identify the type and so prevent damage.

For the past 20 or so years most manufacturers have used the same
sized centre pin, but the 50 Ohm version has a PTFE skirt in order to
provide the correct charateristic impedance. So they are now
mechanically interchangeable.

UKM

[Gaius]

In article fda40c34-830f-438d-830e-0c1c23d2bc44
@c10g2000yqi.googlegroups.com, says...

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.

Can you (or anyone !) provide some evidence of this, in terms of actual
measurements or manufacturers' specifications showing a difference in
the "Old" versions ? You are also confusing the effects of conductor
diameter versus mating surface diameter. 75R and 50R STILL have
different inner conductor diameters to achieve correct Zo; it's the
MATING SURFACES which are the same.

If you plugged a 50 Ohm plug into a 75 Ohm socket the larger centre
pin would splay out the female centre connector, so when you plugged a
75 Ohm back in again it wouldn't make contact. It used to be fairly
common practice to paint the body of the connector purple or green in
order to quickly identify the type and so prevent damage.

I (professionally) used many thousands of BNCs during the timescale you
mention. While it IS true that some 75R sockets could be damaged, in
EVERY case it was due to the inner conductor of the plug being off-
centre. 75R sockets were/are inherently rather fragile.
The problem was caused by a mechanical design weakness in some brands of
plugs (I don't remember which manufacturers).
AFAIR, the BBC used 50R plugs/sockets in some 75R video equipment,
simply because the 50R socket was more robust, by design.

For the past 20 or so years most manufacturers have used the same
sized centre pin, but the 50 Ohm version has a PTFE skirt in order to
provide the correct charateristic impedance. So they are now
mechanically interchangeable.

I have lots of old stock and recovered BNCs dating back at least 20
years. All the 50R and 75R components mate without problem.

[UKMonitor]

On Jun 7, 2:11*pm, Gaius wrote:
In article fda40c34-830f-438d-830e-0c1c23d2bc44
@c10g2000yqi.googlegroups.com, says...

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.

Can you (or anyone !) provide some evidence of this, in terms of actual
measurements or manufacturers' specifications showing a difference in
the "Old" versions ? You are also confusing the effects of conductor
diameter versus mating surface diameter. 75R and 50R STILL have
different inner conductor diameters to achieve correct Zo; it's the
MATING SURFACES which are the same.

If you plugged a 50 Ohm plug into a 75 Ohm socket the larger centre
pin would splay out the female centre connector, so when you plugged a
75 Ohm back in again it wouldn't make contact. It used to be fairly
common practice to paint the body of the connector purple or green in
order to quickly identify the type and so prevent damage.

I (professionally) used many thousands of BNCs during the timescale you
mention. While it IS true that some 75R sockets could be damaged, in
EVERY case it was due to the inner conductor of the plug being off-
centre. 75R sockets were/are inherently rather fragile.
The problem was caused by a mechanical design weakness in some brands of
plugs (I don't remember which manufacturers).
AFAIR, the BBC used 50R plugs/sockets in some 75R video equipment,
simply because the 50R socket was more robust, by design.

For the past 20 or so years most manufacturers have used the same
sized centre pin, but the 50 Ohm version has a PTFE skirt in order to
provide the correct charateristic impedance. So they are now
mechanically interchangeable.

I have lots of old stock and recovered BNCs dating back at least 20
years. All the 50R and 75R components mate without problem.

Well I've got some old 75 Ohm female to female adaptors in front of
me, marked RS part number 455-933 (but the type associated with the
part number has changed many times over the years). I also have one
marked G37534 which looks fairly similar. Most have been opened up
because they have had a 50 Ohm shoved into them.

However on the one pristine 75 Ohm adaptor I could find, the outer
part of the 75 Ohm centre receptacle is so narrow it would easily fit
the inside of a 50 Ohm centre receptacle.

Unfortunately I can’t find any old Greenpar (or similar) mechanical
drawings on the web only the newer types.

UKM

[UKMonitor]

On Jun 7, 3:02*pm, UKMonitor wrote:
On Jun 7, 2:11*pm, Gaius wrote:





In article fda40c34-830f-438d-830e-0c1c23d2bc44
@c10g2000yqi.googlegroups.com, says...

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.

Can you (or anyone !) provide some evidence of this, in terms of actual
measurements or manufacturers' specifications showing a difference in
the "Old" versions ? You are also confusing the effects of conductor
diameter versus mating surface diameter. 75R and 50R STILL have
different inner conductor diameters to achieve correct Zo; it's the
MATING SURFACES which are the same.

If you plugged a 50 Ohm plug into a 75 Ohm socket the larger centre
pin would splay out the female centre connector, so when you plugged a
75 Ohm back in again it wouldn't make contact. It used to be fairly
common practice to paint the body of the connector purple or green in
order to quickly identify the type and so prevent damage.

I (professionally) used many thousands of BNCs during the timescale you
mention. While it IS true that some 75R sockets could be damaged, in
EVERY case it was due to the inner conductor of the plug being off-
centre. 75R sockets were/are inherently rather fragile.
The problem was caused by a mechanical design weakness in some brands of
plugs (I don't remember which manufacturers).
AFAIR, the BBC used 50R plugs/sockets in some 75R video equipment,
simply because the 50R socket was more robust, by design.

For the past 20 or so years most manufacturers have used the same
sized centre pin, but the 50 Ohm version has a PTFE skirt in order to
provide the correct charateristic impedance. So they are now
mechanically interchangeable.

I have lots of old stock and recovered BNCs dating back at least 20
years. All the 50R and 75R components mate without problem.

Well I've got some old 75 Ohm female to female adaptors in front of
me, marked RS part number 455-933 (but the type associated with the
part number has changed many times over the years). I also have one
marked G37534 which looks fairly similar. Most have been opened up
because they have had a 50 Ohm shoved into them.

However on the one pristine 75 Ohm adaptor I could find, the outer
part of the 75 Ohm centre receptacle is so narrow it would easily fit
the inside of a 50 Ohm centre receptacle.

Unfortunately I can’t find any old Greenpar (or similar) mechanical
drawings on the web only the newer types.

UKM- Hide quoted text -

- Show quoted text -

Looks like they were prior to IEC 169-8 (1978) which defined
mechanical interchangeability.

UKM

[Jeff Liebermann[_2_]]

On Mon, 7 Jun 2010 14:11:58 +0100, Gaius wrote:

In article fda40c34-830f-438d-830e-0c1c23d2bc44
, says...

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.

Can you (or anyone !) provide some evidence of this, in terms of actual
measurements or manufacturers' specifications showing a difference in
the "Old" versions ?

I downloaded the mechanical drawings from the Amphenol web pile and
found that the center pin diameter is missing from the drawings. I'll
look elsewhere when I have time.
http://www.amphenolconnex.com/products/bnc.asp

I have a box full of 75 coax patch cables I salvaged from a radio
station cleanup. They all mate fine with a 50 ohm BNC jack. The only
difference is that the 75 ohm plug has no dielectric, while the 50 ohm
jack does.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Jim Lux]

Jeff Liebermann wrote:
On Mon, 7 Jun 2010 14:11:58 +0100, Gaius wrote:

In article fda40c34-830f-438d-830e-0c1c23d2bc44
@c10g2000yqi.googlegroups.com, says...

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.
Can you (or anyone !) provide some evidence of this, in terms of actual
measurements or manufacturers' specifications showing a difference in
the "Old" versions ?

I downloaded the mechanical drawings from the Amphenol web pile and
found that the center pin diameter is missing from the drawings. I'll
look elsewhere when I have time.
http://www.amphenolconnex.com/products/bnc.asp

I have a box full of 75 coax patch cables I salvaged from a radio
station cleanup. They all mate fine with a 50 ohm BNC jack. The only
difference is that the 75 ohm plug has no dielectric, while the 50 ohm
jack does.



http://www.wbdg.org/ccb/FEDMIL/prf39012_16h.pdf is the MIL drawing for
the plug.
note they only have ONE drawing for the center contact.

They also call out MIL-STD-348 for the pin contact interface.
http://www.dscc.dla.mil/Programs/Mil...oc=MIL-STD-348
http://www.dscc.dla.mil/Downloads/Mi...8/idstd348.pdf
is probably the one you want.

on the plug/pin, dimension C (the ID of the insulation inside the outer
conductor) has a minimum, but no maximum.

Likewise on the socket, dimension E, which mates with dimension C on the
plug does have a maximum, but no minimum, implying you can have a "no
dielectric" version.

Dimension D on the plug (the pin diameter) has only one value 0.052 to
0.054 inches.

Dim M on the socket (OD of center conductor) is 0.081 to 0.089,
presumably to correspond roughly with dimension R on the plug, which is
the same.

[Ian Jackson[_2_]]

In message , Owen Duffy
writes
"Geoffrey S. Mendelson" wrote in
:



1. Can I connect a 75ohm BNC plug (which is a different size) to a
50oHm BNC socket?

There is such a thing as a 75 ohm BNC connector, but you are almost
certainly looking at 50 ohm connectors designed for use on 75 ohm cable.
My recollection is that the 75 ohm connectors are incompatible with the
50 ohm connectors, and in some combinations will spread the female inner
part.

For all intents and purposes, 50 and 75 ohm BNCs (both male and female)
are interchangeable. They have essentially the same dimensions. You
might just see that the 50 ohm male has a rather stubby point, whereas
the 75 ohm version has a somewhat more steadily-tapered pin - but,
unlike N-connectors, the 50 ohm male certainly doesn't cause damage to a
75 ohm female.

The thing which mainly causes the impedances to differ is the amount of
PTFE dielectric present, in both sexes. On the 75 ohm version, you will
normally see that it has been reduced considerably compared with the 50
ohm. Even with less dielectric, the 75 ohm version is still a bit
unhappy with having too much, and this tends to lower the impedance to
somewhat less than 75 ohms.

However, for all intents and purposes, you probably won't notice any
significant difference between 50 and 75 ohm BNCs (mixed or not).
--
Ian

[Gaius]

Time to sum up where we are in this cause célèbre, I think.

The diameter of the centre pin in current production BNC plugs is
specified as between 1.32 and 1.37mm (0.052 and 0.054 inches). This is
the same for 75R connectors which are detailed in MIL-STD-348B (9Feb
2009), and 50R connectors, shown in MIL-STD-348 (20 April 1988). The
earlier document does not refer to the Zo, but the drawing is clearly of
a 50R socket with the extended dielectric surrounding the split pin.

Therefore - all compliant BNC connectors are mechanically compatible
between 50R and 75R from April 1988 onwards. There are NO mating damage
problems for current production items.

It has been suggested that prior to the introduction of IEC 169-8 in
1978, which defined interchangeability, there may have been differences
in the pin diameters between 50R and 75R plugs. This will only be
resolved by the actual measurement of plugs known to have been
manufactured prior to 1978 - or someone producing specification
documents from the time.

The definitive specification of BNC connectors would appear to be
contained within IEC standard document 169-8. This does not seem to be
easily available - copies must be purchased at considerable expense from
the IEC. Has anyone got access to a copy of this document ?

[Roy Lewallen]

N connectors don't have any dielectric in the mating region, so the pin
diameter would have to be made smaller for a 75 ohm impedance. Maybe N
connector incompatibility issues have morphed into misconceptions about
BNCs. I don't think I have any 75 ohm N connectors (assuming such things
exist) to look at.

Roy Lewallen, W7EL

[Ian Jackson[_2_]]

In message , Roy Lewallen
writes
N connectors don't have any dielectric in the mating region, so the pin
diameter would have to be made smaller for a 75 ohm impedance. Maybe N
connector incompatibility issues have morphed into misconceptions about
BNCs. I don't think I have any 75 ohm N connectors (assuming such
things exist) to look at.

That certainly explains why the diameter of the 75 ohm N pin is much,
much less than the 50 ohm. The two are certainly not mateable.

I must admit that, in the back of my mind, I'd occasionally wondered why
- and now, after over 46 years of successfully not getting them mixed up
too often (at work, it was a hanging offence to put a 50 ohm male in a
75 ohm female), all is clear! I don't know why it never dawned on me.
I'm fully familiar with the difference between the BNCs.
--
Ian