BNC Question
Interestingly, 50 and 75-ohm BNC connectors have the same pin/shell
dimensions and properly couple together. For more information go to
http://www.cliftonlaboratories.com/august_2007.htm
(http://www.cliftonlaboratories.com/august_2007.htm) and scroll down to the 02 August 2007 entry. There is a
link to the Amphenol site for specifics about the connectors.
I am planning to use an Extron video distribution amplifier for standard
frequency distribution. The 75-ohm connectors will be OK. These amplifiers
feed multiple 75-ohm outputs from a "zero-impedance" source by inserting a
75-ohm resistor in each leg. Some folks using these for standard
frequency distribution change the resistors to 50-ohms.
Bruce, KG6OJI
Sorri, I must have been thinking type N connectors.
Stan, W1LE
On 4/9/2011 8:18 PM, Brucekareen@aol.com wrote:
Interestingly, 50 and 75-ohm BNC connectors have the same pin/shell
dimensions and properly couple together. For more information go to
http://www.cliftonlaboratories.com/august_2007.htm
(http://www.cliftonlaboratories.com/august_2007.htm) and scroll down to the 02 August 2007 entry. There is a
link to the Amphenol site for specifics about the connectors.
I am planning to use an Extron video distribution amplifier for standard
frequency distribution. The 75-ohm connectors will be OK. These amplifiers
feed multiple 75-ohm outputs from a "zero-impedance" source by inserting a
75-ohm resistor in each leg. Some folks using these for standard
frequency distribution change the resistors to 50-ohms.
Bruce, KG6OJI
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No Stan, you are correct.
True 75 ohm BNCs (and Ns and TNCs as well) use a substantially
smaller center pin and no insulation support around the female contacts.
Mating a 50 ohm spec male part (plug) will invariably damage a 75 ohm
female (receptacle.)
Amphenol made a proprietary series that maintained specs to 4 or so
Ghz when mated in the proper system impedance and would reliably
interate without damage. This was not a full spec part, but a
proprietary variant that was a market response to the damage probelms.
They were widely used in broadcast video, and rarely used in RF
applications.
If need be we can pull the mil drawings as a group and compare them. I
learned this lesson by proxy in the days I worked for a cable TV
manufacturer and a tech made the mistake for a second time and got his
pay docked the repair cost from HP. Fortunately, the parts cost was
small. Unfortunately he got to pay for a new cal on the instrument,
about 2 weeks pay for him before withholding.
Rich, N1OZ
On 4/9/2011 9:28 PM, Stan, W1LE wrote:
Sorri, I must have been thinking type N connectors.
Stan, W1LE
On 4/9/2011 8:18 PM, Brucekareen@aol.com wrote:
Interestingly, 50 and 75-ohm BNC connectors have the same pin/shell
dimensions and properly couple together. For more information go to
http://www.cliftonlaboratories.com/august_2007.htm
(http://www.cliftonlaboratories.com/august_2007.htm) and scroll
down to the 02 August 2007 entry. There is a
link to the Amphenol site for specifics about the connectors.
I am planning to use an Extron video distribution amplifier for standard
frequency distribution. The 75-ohm connectors will be OK. These
amplifiers
feed multiple 75-ohm outputs from a "zero-impedance" source by
inserting a
75-ohm resistor in each leg. Some folks using these for standard
frequency distribution change the resistors to 50-ohms.
Bruce, KG6OJI
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To unsubscribe, go to
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--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)
As pointed out earlier (by Bruce and others), there is a vast quantity of 75 ohm BNC connectors which mate perfectly with 50 ohm BNC sockets (save for impedance mismatch). I have a set of 10 cables bought off the *bay with such connectors. These cables are 75 ohm, so there will be a mismatch in a 50 ohm system no matter what the connector is.
I am not sure what would make those less true that anything else. I am sure the mismatch of the connectors themselves, within the frequency range they are intended for will be well below the level where most would care.
If you try to use BNC for precision RF measurements, be prepared to be surprised.
Unless the argument is about what they "should" be, what the standard says is irrelevant when you have a box of parts and wonder if you can used them.
Don't assume anything, just check before you plug.
Didier KO4BB
Sent from my BlackBerry Wireless thingy while I do other things...
-----Original Message-----
From: Oz-in-DFW lists@ozindfw.net
Sender: time-nuts-bounces@febo.com
Date: Sat, 16 Apr 2011 13:23:30
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] BNC Question
No Stan, you are correct.
True 75 ohm BNCs (and Ns and TNCs as well) use a substantially
smaller center pin and no insulation support around the female contacts.
Mating a 50 ohm spec male part (plug) will invariably damage a 75 ohm
female (receptacle.)
Amphenol made a proprietary series that maintained specs to 4 or so
Ghz when mated in the proper system impedance and would reliably
interate without damage. This was not a full spec part, but a
proprietary variant that was a market response to the damage probelms.
They were widely used in broadcast video, and rarely used in RF
applications.
If need be we can pull the mil drawings as a group and compare them. I
learned this lesson by proxy in the days I worked for a cable TV
manufacturer and a tech made the mistake for a second time and got his
pay docked the repair cost from HP. Fortunately, the parts cost was
small. Unfortunately he got to pay for a new cal on the instrument,
about 2 weeks pay for him before withholding.
Rich, N1OZ
On 4/9/2011 9:28 PM, Stan, W1LE wrote:
Sorri, I must have been thinking type N connectors.
Stan, W1LE
On 4/9/2011 8:18 PM, Brucekareen@aol.com wrote:
Interestingly, 50 and 75-ohm BNC connectors have the same pin/shell
dimensions and properly couple together. For more information go to
http://www.cliftonlaboratories.com/august_2007.htm
(http://www.cliftonlaboratories.com/august_2007.htm) and scroll
down to the 02 August 2007 entry. There is a
link to the Amphenol site for specifics about the connectors.
I am planning to use an Extron video distribution amplifier for standard
frequency distribution. The 75-ohm connectors will be OK. These
amplifiers
feed multiple 75-ohm outputs from a "zero-impedance" source by
inserting a
75-ohm resistor in each leg. Some folks using these for standard
frequency distribution change the resistors to 50-ohms.
Bruce, KG6OJI
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)
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and follow the instructions there.
On 4/16/2011 2:59 PM, shalimr9@gmail.com wrote:
As pointed out earlier (by Bruce and others), there is a vast quantity of 75 ohm BNC connectors which mate perfectly with 50 ohm BNC sockets (save for impedance mismatch). I have a set of 10 cables bought off the *bay with such connectors. These cables are 75 ohm, so there will be a mismatch in a 50 ohm system no matter what the connector is.
No doubt, but I think you'll also find these are the Amphenol
proprietary parts - which will damage the MIL-STD 75 ohm parts that HP
and a lot of other vendors used for a long time, just damaged less
frequently.
I am not sure what would make those less true that anything else.
Strictly speaking, BNC, TNC, and N are rooted in MIL-STDs from the
fourties, the other stuff intermates and has improvements of varying
nature. This gets into detailed semantics. Are the cheapie import
connectors that can't sweep past 100 Mhz Ns or something else? They
intermate, but they don't work so well.
I am sure the mismatch of the connectors themselves, within the frequency range they are intended for will be well below the level where most would care.
Right, but the issue was intermating and damaging one type with another
and poor mating reliability. The fact is that there ARE BNC (and N and
TNC) variants that will have this problem. There are a number of folks
here who have flatly stated that this is not the case, but it really is.
If you try to use BNC for precision RF measurements, be prepared to be surprised.
BNCs can be as good as TNCs when properly applied, but the bayonet
mechanism allows too much mechanical alignment play for reasonable
reliability past a GHz or so. If they are properly installed and the
cable is not allowed to put a radial or significant tensile load they
perform as well as a TNC and close to an N. For all that, I won't use
them in designs above 100 Mhz without a compelling reason. F's are
cheaper, and SMAs are more reliable. If it's hard coded at 75 ohms and
related to measuremnts - I use Ns.
Unless the argument is about what they "should" be, what the standard says is irrelevant when you have a box of parts and wonder if you can used them.
I think we're in 'violent agreement' here. My point is that you need to
be aware of the many variations of connectors that have appeared in the
last 50+ years and use care lest you end up with an undesired repair.
Don't assume anything, just check before you plug.
And this is the point. There are connectors that will not reliably
intermate and will be damaged. This is true in BNC as well as N and TNC.
Didier KO4BB
--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)
HP made a point of telling users that the 75 ohm female BNC connectors used
on HP equipment were fully and safely mate-able with standard male 50 ohm
parts. This has been so certainly from the 1970's. Casual inspection of
the part shows that it uses the identical center pin set as the 50 ohm
parts.
-Chuck Harris
Oz-in-DFW wrote:
On 4/16/2011 2:59 PM, shalimr9@gmail.com wrote:
As pointed out earlier (by Bruce and others), there is a vast quantity of 75 ohm
BNC connectors which mate perfectly with 50 ohm BNC sockets (save for impedance
mismatch). I have a set of 10 cables bought off the *bay with such connectors.
These cables are 75 ohm, so there will be a mismatch in a 50 ohm system no
matter what the connector is.
No doubt, but I think you'll also find these are the Amphenol proprietary parts -
which will damage the MIL-STD 75 ohm parts that HP and a lot of other vendors used
for a long time, just damaged less frequently.
I am not sure what would make those less true that anything else.
Strictly speaking, BNC, TNC, and N are rooted in MIL-STDs from the fourties, the
other stuff intermates and has improvements of varying nature. This gets into
detailed semantics. Are the cheapie import connectors that can't sweep past 100
Mhz Ns or something else? They intermate, but they don't work so well.
I am sure the mismatch of the connectors themselves, within the frequency range
they are intended for will be well below the level where most would care.
Right, but the issue was intermating and damaging one type with another and poor
mating reliability. The fact is that there ARE BNC (and N and TNC) variants that
will have this problem. There are a number of folks here who have flatly stated
that this is not the case, but it really is.
If you try to use BNC for precision RF measurements, be prepared to be
surprised.
BNCs can be as good as TNCs when properly applied, but the bayonet mechanism
allows too much mechanical alignment play for reasonable reliability past a GHz or
so. If they are properly installed and the cable is not allowed to put a radial
or significant tensile load they perform as well as a TNC and close to an N. For
all that, I won't use them in designs above 100 Mhz without a compelling reason.
F's are cheaper, and SMAs are more reliable. If it's hard coded at 75 ohms and
related to measuremnts - I use Ns.
Unless the argument is about what they "should" be, what the standard says is
irrelevant when you have a box of parts and wonder if you can used them.
I think we're in 'violent agreement' here. My point is that you need to be aware
of the many variations of connectors that have appeared in the last 50+ years and
use care lest you end up with an undesired repair.
Don't assume anything, just check before you plug.
And this is the point. There are connectors that will not reliably intermate
and will be damaged. This is true in BNC as well as N and TNC.
Didier KO4BB
Oz-in-DFW wrote:
BNCs can be as good as TNCs when properly applied, but the bayonet
mechanism allows too much mechanical alignment play for reasonable
reliability past a GHz or so. If they are properly installed and the
cable is not allowed to put a radial or significant tensile load they
perform as well as a TNC and close to an N. For all that, I won't use
FWIW:
The guts of a BNC/TNC is very similar if not identical to a type N,
which is good for at least 12.4 GHz. The Agilent 13 GHz scopes
have "precision" (IE tight fitting) BNC connectors on the probes.
All of which of course doesn't mean the Asian BNC's you bought
at the hamfest are any good.
Rick N6RK
Rick Karlquist wrote:
FWIW:
The guts of a BNC/TNC is very similar if not identical to a type N,
which is good for at least 12.4 GHz. The Agilent 13 GHz scopes
have "precision" (IE tight fitting) BNC connectors on the probes.
All of which of course doesn't mean the Asian BNC's you bought
at the hamfest are any good.
Rick N6RK
There is a very significant difference between the N and the BNC
construction with regards to what is the insulator in the transition
section between the male and female connector: With the BNC (and TNC)
connector(s), the space is filled with an interdigitated plastic
dielectric. With the N, the space is filled with air.
-Chuck Harris