In article ,
says...


A 75 ohm BNC plug is identical to a 50 ohm
one, save that the male pin in a 75 ohm plug is smaller in diameter.
The other way round, a 50 ohm BNC plug will damage a 75 ohm BNC socket.

Sorry. Not so. This is one of the most common urban myths in RF
engineering. The pin diameters of BNCs are identical between 50 and 75R.
(Measure them !!)

The 50R and 75R connectors are mechanically compatible in BOTH
directions. Don't take my word for it - check Amphenol's specifications:
"Two distinct types of 75ohm BNCs are available, and both mate with each
other and with 50ohm BNCs. "

I've been using 75R and 50R interchangeably for about thirty years, and
I've had NO mating damage problems. (Mismatches don't worry me - HF
only).

Note - type N and type C connectors WILL be damaged if you try to mix
75R and 50R varieties. I suspect this is the source of the BNC myth.

Also - some Chinese made BNCs are so badly made that they will damage
other connectors - but this is a manufacturing tolerance issue.

Hi Gaius,
Gaius Inscribed thus:

In article ,
says...


A 75 ohm BNC plug is identical to a 50 ohm
one, save that the male pin in a 75 ohm plug is smaller in diameter.
The other way round, a 50 ohm BNC plug will damage a 75 ohm BNC
socket.

Thats what I said... :-(

Sorry. Not so. This is one of the most common urban myths in RF
engineering. The pin diameters of BNCs are identical between 50 and
75R. (Measure them !!)

I did... :-(

The 50R and 75R connectors are mechanically compatible in BOTH
directions. Don't take my word for it - check Amphenol's
specifications: "Two distinct types of 75ohm BNCs are available, and
both mate with each other and with 50ohm BNCs. "

I did check that documentation... :-(

I've been using 75R and 50R interchangeably for about thirty years,
and I've had NO mating damage problems. (Mismatches don't worry me -
HF only).

I've probably used them for nearer 50 years, and had to replace damaged
sockets because the bifurcated female pin had one side broken off. I
am aware that some of the early plugs didn't have solidly captive pins
and could move forward and cause damage. Greenpar package the
plugs/sockets clearly marked 50 or 75 ohm. In all that time I've never
bothered to check the specifications until now.

Note - type N and type C connectors WILL be damaged if you try to mix
75R and 50R varieties. I suspect this is the source of the BNC myth.

Having taken your words and accept that I'm wrong, I can only agree that
you're right and it is a myth.

Thanks for the insight.

Also - some Chinese made BNCs are so badly made that they will damage
other connectors - but this is a manufacturing tolerance issue.

73's
--
Best Regards:
Baron.

On 6/5/2010 5:49 PM, Geoffrey S. Mendelson wrote:
I recently was able to use a crimp on tool for F connectors for RG-6 quad
shield coax. To make sure everyone understands, I am in Israel, and RG-6
quad shield coax is cheap and easy to find.

Any other coax is almost impossible to find. Pl-259 connectors, called
"UHF" connectors here are rare items. I can get them locally, but I have
to special order them and they are expensive. Since I can not see them
before I order them, I am as likely to get nickle plated ones with
phenolic insulation as I am to get any other kind, and once ordered are
not returnable.

BNC to PL-259 adaptors, are easy to get, and can be ordered from a reliable
local souce for a relatively small price. The same with N to PL-259.

Looking around at the crimp-on F connectors before I ordered them, I found
that you can get crimp on BNC connectors for RG-6 quad shield coax.

Here's my questions, Note when I say crimp-on, I mean the ones that crimp
from the rear, like commerical F connectors, not the ones that crimp
around the plug. I have never been able to get any of them to "fit right":

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

No the size of the center conductor pin is different between 75 and 50
ohm connectors and will either make bad contact or damage the socket.


2. Are there crimp on 50 ohm BNC plugs which will work with RG6 quad shield?
I know there are variations, but most are similar in size.


I don't think so, as there are large differences in the diameter of the
2 kinds of coax, both the diameter of the center conductor and the
outside diameter of the coax.

3. Are there crimp on N connectors that would fit the RG6 quad shield coax?
More likely due to the size a crimp on center element that screws into the
plug body?

I've never seen any and can't think of any commercial reason that anyone
would make one.

4. Are there crimp on PL-259 connectors?

Yes, I use them all the time. I like them much better than the solder on
type. Most need the center pin soldered but the crimp connection to the
shield is much easier and better done than when soldered

Thanks in advance,

Geoff.



It's my experience that Teflon insulated PL259's are inferior to the
phenolic insulation type. The PL259 is a non constant impedance
connector that gains no benefit from Teflon insulation as to impedance.
The ability of Teflon to hold the center pin in placed is greatly
inferior to phenolic. One of the advertised benefits of Teflon is to
withstand more heat, true but by the time the connector is heated enough
to hurt the phenolic, the coax your trying to install is melted way.
Nickel is harder to solder to than silver but the real problem with
cheap PL259s is the inside diameter of the area with holes your supposed
to solder through. I've measured a few and found them to uniformly to
have a too big of an inside diameter. This means there is a larger gap
between the metal of the connector and the shield than should be. This
gap is hard to impossible to fill with solder and makes for poor heat
transfer to the braid of the shield. Finding good connectors is much
harder than it used to be as most high-end equipment manufacture are not
using PL259s anymore and what hams can get are largely junk I'm afraid.
I've seen on ham equipment SO239, the jack half, ones that were molded
metal instead of machined brass. Those are hard to thread on a plug onto
and are of a soft pot metal that cracks or binds.


John Passaneau W3JXP

John Passaneau wrote:
On 6/5/2010 5:49 PM, Geoffrey S. Mendelson wrote:

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

No the size of the center conductor pin is different between 75 and 50
ohm connectors and will either make bad contact or damage the socket.

That's not necessarily true. I have some RG-59 cables with male 75 ohm
BNC connectors that mate fine with 50 ohm connectors. The diameter of
the 75 ohm connector center pin is the same diameter as 50 ohm
connectors. The difference is that the dielectric surrounding the center
pin of the 75 ohm connector is much thinner. And at the point where the
pin enters the solid dielectric at the bottom, the 75 ohm pin doesn't
step up in diameter.

Others have said that there are some 75 ohm BNC connectors which won't
interconnect without damage. But I do know there are some that mate with
no problem. 50 ohm BNC connectors and adapters are very common. I
suggest you get one and compare the center pin diameter with that of
your 75 ohm connector. If it's the same, the two can interconnect
without damage.

I also have a lot of RG-59 cables with 50 ohm BNC connectors. That's
probably more common, since 50 ohm connectors are much more common, and
the connector choice won't make any practical difference in the vast
majority of applications.

Roy Lewallen, W7EL

In article , says...

No the size of the center conductor pin is different between 75 and 50
ohm connectors and will either make bad contact or damage the socket.

Please support that allegation with evidence.

What are the specified diameters of the inner conductor mating surfaces
of 75R and 50R BNC plugs ?

Include allowable manufacturing tolerances, and quote your sources.

On Sun, 06 Jun 2010 17:17:25 -0700, Roy Lewallen
wrote:

I also have a lot of RG-59 cables with 50 ohm BNC connectors. That's
probably more common, since 50 ohm connectors are much more common, and
the connector choice won't make any practical difference in the vast
majority of applications.

Just a minor note, but coaxial cable Arcnet connectors, using 93 ohm
RG-62a/u coax cable, also used 50 ohm BNC connectors. The terminators
were 93 ohm resistors inside 50 ohm BNC connectors:
http://theory.cs.uni-bonn.de/info5/system/arcnet.html

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

Roy Lewallen wrote:
I also have a lot of RG-59 cables with 50 ohm BNC connectors. That's
probably more common, since 50 ohm connectors are much more common, and
the connector choice won't make any practical difference in the vast
majority of applications.

Well, we will see in a couple of weeks what I get. I broke down and bought
a set consisting of a BNC crimping tool, a wire stripper and 50 rg-59
BNC plugs from an eBay store.

They did not have any rg-6 plugs, so I'm hoping that the RG6-QS I've got
works.

It's the heavy duty kind that looks like a heavy duty side crimp tool, except
that the wire goes in the top and the plug is pushed together from the handle
end (bottom).

I'll report back.

Thanks for all the help and support so far.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.

On Mon, 7 Jun 2010 02:24:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Well, we will see in a couple of weeks what I get. I broke down and bought
a set consisting of a BNC crimping tool, a wire stripper and 50 rg-59
BNC plugs from an eBay store.

What's the item number? I'll check if you bought the correct
connectors for RG-6a/u QS coax.

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

Jeff Liebermann wrote:
On Mon, 7 Jun 2010 02:24:04 +0000 (UTC), "Geoffrey S. Mendelson"

What's the item number? I'll check if you bought the correct
connectors for RG-6a/u QS coax.

Thanks.

380197598600

Though to be honest, if they are not the correct ones, I'll still probably
use them anyway.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.

Jeff Liebermann wrote in
:

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