altinex switches
Hi Chuck,
some early 75R BNC designs did use a smaller diameter center contact. The 75R male can make intermittent contact when used with a worn or top of limit 50R female. The 75R female can be damaged for use with the small contact male if used with a 50R or large contact 75R male. The do exist, but are pretty rare. A lot got changed out as faulty. I've not seen one on any modern (last 20 years) equipment.
Robert G8RPI.
From: Chuck Harris cfharris@erols.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, 22 February 2013, 6:15
Subject: Re: [time-nuts] altinex switches
In general, no, they are not. The connector pins for modern 75ohm
BNC's are exactly the same part as for modern 50 ohm BNC's. The BNC
gets the higher impedance inside of the connection area by removing
most of the inner dielectric.
The real problem child, in general, is the female 75 ohm N connector,
vs the male 50 ohm N connector. In this case, the connector has no
dielectric in the mating area, so in order to keep the impedance
constant, it has to have a smaller diameter center conductor on the
75 ohm variant. If you attempt to mate a 50 ohm male N connector
with a 75 ohm female N connector, you will split out the female
center socket pin.
Legend has it that there were some variations of the 75 ohm BNC that
don't work with 50 ohm variety.... I can't speak to whether or not
that is true, only that in my 40 years in the business, I have never
seen one where there was a problem.
-Chuck Harris
paul swed wrote:
Good point Bob the 75 ohms are smaller in diameter. I use 75 ohm connectors.
The 50 into a 75 hole spreads the jack.
Regards
Paul
WB8TSL
On Thu, Feb 21, 2013 at 4:16 PM, Bob Camp lists@rtty.us wrote:
Hi
Be careful with the BNC connectors on those switches. 75 ohm BNC's aren't
the same as 50 ohm connectors. The inner contact is different enough that
they don't always play well together.
Bob
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.
Hi Robert,
The only way it would make sense to make the center pin diameter
smaller on a 75 ohm BNC is if the center section of the connector
has dielectric in it. So, I would venture then that if you find a
75 ohm BNC that has dielectric in the mating area, around the pin,
it will be a problem.
The original coax illustrates this action. Some of the earliest
commercial coax was air insulated, and had optimally sized center
and shield diameters for low loss power transmission. Which results
in 75 ohm impedance. It was a dodgy affair, as it had very thin
lucite disks every foot, or so, that kept the center conductor
centered in the shield. This worked ok for rigid coax, and even
semi-rigid coax where large radius arcs, over long runs, are
possible... like on an antenna tower, or a intercontinental under
sea telephone trunk cable...
At some point, it became desirable to make short flexible runs of
coax, WWII as I recall, and the disk scheme wasn't optimal, so the
coax was entirely filled with polyethylene plastic, and because of
the dielectric constant of the polyethylene, the 75 ohm air
dielectric impedance dropped to 50 ohm. The loss went way up, but
flexibility trumped loss in short pigtails for interconnecting cables,
and 50 ohm became popular.... RG-8 coax was born.
-Chuck Harris
Robert Atkinson wrote:
Hi Chuck, some early 75R BNC designs did use a smaller diameter center contact.
The 75R male can make intermittent contact when used with a worn or top of limit
50R female. The 75R female can be damaged for use with the small contact male if
used with a 50R or large contact 75R male. The do exist, but are pretty rare. A
lot got changed out as faulty. I've not seen one on any modern (last 20 years)
equipment.
Robert G8RPI.
Hi
Using common WWII coax materials, 75 ohms is roughly the minimum loss per
foot design. 50 ohms is the maximum power handling design. The low loss /
high power duality is what still has us matching transmitters into 50 ohms
and running cable TV at 75 ohms.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Chuck Harris
Sent: Friday, February 22, 2013 9:40 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] altinex switches
Hi Robert,
The only way it would make sense to make the center pin diameter
smaller on a 75 ohm BNC is if the center section of the connector
has dielectric in it. So, I would venture then that if you find a
75 ohm BNC that has dielectric in the mating area, around the pin,
it will be a problem.
The original coax illustrates this action. Some of the earliest
commercial coax was air insulated, and had optimally sized center
and shield diameters for low loss power transmission. Which results
in 75 ohm impedance. It was a dodgy affair, as it had very thin
lucite disks every foot, or so, that kept the center conductor
centered in the shield. This worked ok for rigid coax, and even
semi-rigid coax where large radius arcs, over long runs, are
possible... like on an antenna tower, or a intercontinental under
sea telephone trunk cable...
At some point, it became desirable to make short flexible runs of
coax, WWII as I recall, and the disk scheme wasn't optimal, so the
coax was entirely filled with polyethylene plastic, and because of
the dielectric constant of the polyethylene, the 75 ohm air
dielectric impedance dropped to 50 ohm. The loss went way up, but
flexibility trumped loss in short pigtails for interconnecting cables,
and 50 ohm became popular.... RG-8 coax was born.
-Chuck Harris
Robert Atkinson wrote:
Hi Chuck, some early 75R BNC designs did use a smaller diameter center
contact.
The 75R male can make intermittent contact when used with a worn or top of
limit
50R female. The 75R female can be damaged for use with the small contact
male if
used with a 50R or large contact 75R male. The do exist, but are pretty
rare. A
lot got changed out as faulty. I've not seen one on any modern (last 20
years)
equipment.
Robert G8RPI.
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.
Actually max power is around 30 ohms. Fifty ohms was a compromise.
Here is a good paper on coax design.
Regards,
Tom
----- Original Message -----
From: "Bob Camp" lists@rtty.us
To: "'Discussion of precise time and frequency measurement'"
time-nuts@febo.com
Sent: Friday, February 22, 2013 11:11 AM
Subject: Re: [time-nuts] altinex switches
Hi
Using common WWII coax materials, 75 ohms is roughly the minimum loss per
foot design. 50 ohms is the maximum power handling design. The low loss /
high power duality is what still has us matching transmitters into 50 ohms
and running cable TV at 75 ohms.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Chuck Harris
Sent: Friday, February 22, 2013 9:40 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] altinex switches
Hi Robert,
The only way it would make sense to make the center pin diameter
smaller on a 75 ohm BNC is if the center section of the connector
has dielectric in it. So, I would venture then that if you find a
75 ohm BNC that has dielectric in the mating area, around the pin,
it will be a problem.
The original coax illustrates this action. Some of the earliest
commercial coax was air insulated, and had optimally sized center
and shield diameters for low loss power transmission. Which results
in 75 ohm impedance. It was a dodgy affair, as it had very thin
lucite disks every foot, or so, that kept the center conductor
centered in the shield. This worked ok for rigid coax, and even
semi-rigid coax where large radius arcs, over long runs, are
possible... like on an antenna tower, or a intercontinental under
sea telephone trunk cable...
At some point, it became desirable to make short flexible runs of
coax, WWII as I recall, and the disk scheme wasn't optimal, so the
coax was entirely filled with polyethylene plastic, and because of
the dielectric constant of the polyethylene, the 75 ohm air
dielectric impedance dropped to 50 ohm. The loss went way up, but
flexibility trumped loss in short pigtails for interconnecting cables,
and 50 ohm became popular.... RG-8 coax was born.
-Chuck Harris
Robert Atkinson wrote:
Hi Chuck, some early 75R BNC designs did use a smaller diameter center
contact.
The 75R male can make intermittent contact when used with a worn or top of
limit
50R female. The 75R female can be damaged for use with the small contact
male if
used with a 50R or large contact 75R male. The do exist, but are pretty
rare. A
lot got changed out as faulty. I've not seen one on any modern (last 20
years)
equipment.
Robert G8RPI.
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.
Don;
Yes, that seemed to be where I was headed, too. Thanks for responding.
JimT
Sent from my galaxy (Nexus).
On Feb 21, 2013 9:26 PM, "Don Latham" djl@montana.com wrote:
Hi Jim: I had to make up a little 3-pin to 9-pin adapter using loose
pins. It just kinda hangs there...
Don
James Tucker
Don;
I got one of those switchs;very nice product, great price. Wish I'd
bought two!
Do you have a reference for the mating connector for the RS232 by any
chance?
JimT
Sent from my galaxy (Nexus).
On Feb 21, 2013 4:13 PM, "Don Latham" djl@montana.com wrote:
I don't have the manual source offhand, but it will be in my msg
archived. The RS232 does respond, and can also be used to control the
unit I have. I got a nice note from the seller; apparently the
time-nuts
snatched these units up in less than a day...and it was the seller who
put me on to the manual, a typical Google got me nothing. I'll be home
next week, and can supply the manual URL then if you can't find it.
Don
Robert LaJeunesse
I've been known to just stack a 150 Ohm 1% chip resistor on top of a
75
Ohm chip
resistor to bring the result down to 50 Ohms. Beats having to 1)
remove
the old
part, 2) clean up the pads, then 3) get the new one soldered down.
Bob L.
From: Arthur Dent golgarfrincham@yahoo.com
To: "time-nuts@febo.com" time-nuts@febo.com
Sent: Thu, February 21, 2013 4:13:48 PM
Subject: [time-nuts] altinex switches
... it should be easy to switch it to 50 ohms although it may not
make
any real
difference.
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.
--
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
De Erroribus Medicorum, R. Bacon, 13th century.
"If you don't know what it is, don't poke it."
Ghost in the Shell
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com
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.
--
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
De Erroribus Medicorum, R. Bacon, 13th century.
"If you don't know what it is, don't poke it."
Ghost in the Shell
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com
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.