On 24.07.2014 18:00, Ackermann, John R wrote:
Just FWIW, the TADD-1 uses transformers to provide DC isolation, but the
shield side of the coax goes to ground through a 0.1uF cap. The hope is
that this reduces the issue that John's referring to (and which I've
seen plenty of times using
General Radio used to have some common values of capacitances available in
terminator type configuration and passthru/bulkhead type
configuration. These were moderately useful doing some bridge-type
measurements. I remember blowing one up once, and taking it apart being
pretty impressed the
Stefan wrote:
shield side of the coax goes to ground through a 0.1uF cap.
For optimum results with respect to high RF frequencies, I'd expect
that you would need this cap to be annular, so that the cable can
pass through the middle, and the outside connects to the chassis
hole all around.
On 25.07.2014 20:07, Charles Steinmetz wrote:
Stefan wrote:
shield side of the coax goes to ground through a 0.1uF cap.
For optimum results with respect to high RF frequencies, I'd expect
that you would need this cap to be annular, so that the cable can pass
through the middle, and the
On 25.07.2014 15:56, Tim Shoppa wrote:
General Radio used to have some common values of capacitances available in
terminator type configuration and passthru/bulkhead type
configuration. These were moderately useful doing some bridge-type
measurements. I remember blowing one up once, and taking
Stefan wrote:
However, when making shield terminations, many would tell you that
it is important to terminate the shield 360 degrees to the chassis
in order to have the best effect. Surely, that also has to be true
for RF frequencies when you choose to raise the near-DC impedance of
the
-
From: Attila Kinali att...@kinali.ch
To: time-nuts@febo.com
Sent: Saturday, July 19, 2014 3:09 PM
Subject: [time-nuts] Noise and non-linear behaviour of ferrite transformers
Hi,
I'm currently looking at some way of breaking the ground loop between
several systems. The obvious idea would
On 7/20/2014 6:41 AM, John Miles wrote:
I often find that when I use coaxial baluns to cut down on ground loop
noise, I end up with more noise and interference than I started with. Not
always, but often enough that I'm leery of them.
Due to skin effect, most signal propagation in a coaxial
Effectiveness of coax cable (at eliminating the effects of current through the
shield) is often expressed as transfer impedance.
Google it for more info, it has been extensively covered in the literature.
Didier KO4BB
On July 20, 2014 11:18:58 PM CDT, Chuck Harris cfhar...@erols.com wrote:
Hi
If you have an electrostatic field to worry about, a simple shield does a fine
job. If it’s a magnetic field - maybe not so much. A propagating
electromagnetic field is going to be a bit tough to stop.
Again it comes back to Bert’s question - what is the objective?
Bob
On Jul 21, 2014,
, 2014 5:09 PM
Subject: [time-nuts] Noise and non-linear behaviour of ferrite transformers
Hi,
I'm currently looking at some way of breaking the ground loop between
several systems. The obvious idea would be to use transformers. I would
like to have some kind of rule of thumb to guess how much
On 7/19/2014 6:38 PM, Richard (Rick) Karlquist wrote:
Or
another way of putting it is you do a bunch of
measurements and then construct a theory to
explain what you already know experimentally.
I like that. Or perhaps, stated another way, in the real world engineers
are just as important as
Good morning!
On Sat, 19 Jul 2014 18:38:17 -0700
Richard (Rick) Karlquist rich...@karlquist.com wrote:
I did some tests of residual phase noise using an
Agilent E5505A and found that air coil inductors
did not add noise (at least down to my noise threshold)
but that ferrite core inductors
On Sat, 19 Jul 2014 22:16:33 -0700
John Miles j...@miles.io wrote:
That may be due to tempco, as Tom mentioned. The ferrite cores don't seem
to be noisy in and of themselves,
My current research tells me, that transformers have an inherent
noise (Barkhausen noise), but so far i could not
All that said, the real hazard with transformers is that people tend to
use
them to drive unbalanced coax cables with balanced signals. This turns
the
coax shield into an antenna, at which point you may end up with with
more
noise and spurs than you had before.
Could you explain this a
Moin,
On Sun, 20 Jul 2014 03:41:44 -0700
John Miles j...@miles.io wrote:
I often find that when I use coaxial baluns to cut down on ground loop
noise, I end up with more noise and interference than I started with. Not
always, but often enough that I'm leery of them.
[...]
Thanks for the
I've seen a few pieces of equipment that use a transformer-coupled
output and an isolated BNC jack to break any ground loops. Then they
connect the shield to the chassis with a parallel RC network. The C
might be in the 1-10 nf range while the R is a few hundred ohms. I know
of one piece of
Hi
The simple way to take care of the coax shield issue is to use a common mode
choke.
Bob
On Jul 20, 2014, at 12:16 PM, Attila Kinali att...@kinali.ch wrote:
Moin,
On Sun, 20 Jul 2014 03:41:44 -0700
John Miles j...@miles.io wrote:
I often find that when I use coaxial baluns to cut
Hi
With the Cap to ground, you “short out” the transformer at RF. The resistor
takes care of static, and if it’s low enough shorts out the transformer at
lower frequency.
More or less - you break the 60Hz ground loop (sort of). You do very little for
RF isolation.
Bob
On Jul 20, 2014, at
Common mode choke works fine for RF, hard to reject 60Hz ground loop
currents using ferrites. (Although there is a website I found once where
the guy shows an entire bucket of miscellaneous ferrites cobbled together
for a common mode choke!) For a DC-to-daylight instrument that is suffering
60Hz
Attila you do not need triax cable, a good coax will do the job, but
open shield is always a source of trouble, just imagine there is a vey
good coupled line -- which at certain frequency is n times the 1/4
wave length.
cat 5 or cat 6 you get what you pay for .. it was never made for
Hi
The “coax is an antenna” problem comes in well before you get to DC. Even with
no transformer involved, the skin depth of the coax shield gives up well above
60 Hz (and likely well above 100 KHz). If you want to do full isolation over a
very wide range you need some combination of shielding
I'm not sure what you are saying.
skin depth = (2.6/sqrt(fhz))inches for copper.
So, at 60Hz, skin depth = 0.336 inches.
and at 100KHz, skin depth = 0.008 inches.
and at 1MHz, skin depth = 0.0026 inches.
Are you saying that at 60Hz, because the
skin depth is deeper than the coax shield is
No, the current passing the outside f the shield will not induce any
voltage inside of the coax, but the voltage drop caused by the current
on the ohmic resistance [!!!] of the shield will show upbetween the two
ends of the cable -- and that will show up as it was added to to the
voltage
Hi
Yup
It is impractical to make coax that has a shield thickness of 1/3”. Even if you
do, it’s not going to be very flexible. For a real world system that needs good
isolation, coax is not the way to go below 100 KHz. There are a few other
issues that come up, but skin depth is a big part of
Lots of meanings to the word induce. The one I was using was: to
bring on, or about; effect; cause... I was not intending to imply
transformer action. As an engineer I should know better than to
try to use English to describe electrical phenomenon.
My intention was to find out what: ...the
Hi Bob,
I agree, but most of the time, you can use good design
practices to keep the currents flowing through the outside
of the shield to a minimum... avoiding ground loops, stuff
like that.
Simple coax is used for shielding very high gain circuits
from 60Hz noise all the time in PA systems.
Hi,
I'm currently looking at some way of breaking the ground loop between
several systems. The obvious idea would be to use transformers. I would
like to have some kind of rule of thumb to guess how much noise such
a transformer would add. But unfortunately i cannot find any theory
or
Hi
The general rule of thumb is that they add no noise or distortion. The typical
reason for not using them all the time is cost / size / weight.
A lot depends on what frequency (or frequency band) you are talking about and
what sort of transformers. Obviously you can indeed mis-use a part or
I did some tests of residual phase noise using an
Agilent E5505A and found that air coil inductors
did not add noise (at least down to my noise threshold)
but that ferrite core inductors had easily seen noise.
It was on the order of ADEV = 1E-10 close to the
carrier. I would describe this as
19, 2014 3:09 PM
Subject: [time-nuts] Noise and non-linear behaviour of ferrite transformers
Hi,
I'm currently looking at some way of breaking the ground loop between
several systems. The obvious idea would be to use transformers. I would
like to have some kind of rule of thumb to guess how
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