ULF,
Just to complete this thread of the antenna current measurement by using
Rogowski coils: Here is a photo of the coil that i built, while
measuring a RF current in a guide rail pole, taken during the recent
experiment at 470 Hz.
http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/rog_coil_in_action.jpg
The overall antenna current was 2.2 A. The poles are of course a current
divider. It was most useful to add a 200 mA (100 mA/V) range to the
electronic. Here, the meter shows 48.3 mA.
It is the only method to measure the antenna current into the pole
without modifying the arrangement.
BTW this coil allows to measure RF currents into trees! So, if you have
a tree standing near your antenna and asking how much current it may
absorb, then this method causes much less stress with the XYL than
'temporary' cutting the tree and inserting a shunt resistor.
73, Stefan
Am 29.10.2018 21:28, schrieb DK7FC:
Hi all,
I completed the Rogowski-coil project this evening. Mine is a version
for the SLF/ULF/VLF range, covering 0.1...10 kHz. Of course a version
for LF can be built too.
The coil is now protected with shrinking tube. It feels very robust.
The circuit consumes 8 mA from a 9V battery. It integrates the voltage
to get rid of the di/dt dependency and provides a output voltage of 1V
at 1A RF. This ratio is very stable (< 3%) inside the design frequency
range. Also the linearity is more than adequate. The current range is
0...2A, so the current can be measured with a 2V AC digital multimeter
(covering that frequency range).
The attachemnt shows the portable system which does now allow to
measure RF currents into larger metallic parts, such as towers, or
guide rail poles! :-)
Oh and you can measure the antenna current on the hot side of the
coil, or along the wire, even if it carries 20 kV. The coupling
capacity will be negligible.
A second attachment shows the schematic, just to give an idea.
No, this is not new (unfortunately necessary to mention this, before
someone can't resist to do so)! But anyway i did not see someone else
using such a technique since the almost 10 years i'm here on the
reflector.
Indeed it could be helpful to measure how much antenna current is
still flowing in the wire after some meters where a tree pulls away a
part of it. It may help to check if it is worth to remove the tree,
or, to move the coil behind the tree (on the cost of a lower capacity
and thus higher losses for a larger coil )...
73, Stefan
PS: A practical test will follow in some days...
Am 24.10.2018 20:48, schrieb DK7FC:
...now the coil is completed, see attachment.
Some first measurements:
Diameter: 0.3 m.
R (DC): 17 Ohm.
Inductivity (measured at ~ 1 kHz): 1.62 mH
Self resonance: 734 kHz
So far so good...
73, Stefan
Am 23.10.2018 15:13, schrieb DK7FC:
...now i started to build one, see attachment.
Not yet sure how it will perform. DON'T bother me with calculations
telling it won't work! ;-)
73, Stefan
Am 22.10.2018 15:04, schrieb DK7FC:
Hi all,
Has someone ever build (homemade, not bought!) a Rogowski-coil for
RF current measurements?
https://en.wikipedia.org/wiki/Rogowski_coil
It could be used to measure leakage currents in a tower near the
antenna wire for example. Or for measuring RF currents into a pole
of a guide rail, for example :-)
I'm planning to build one and i thought i use 0.4 mm diameter
enameled cu wire arround a graden hose, having 0.6m circumference.
Then some shrinking tube will be applied. That's the plan.
The circuit looks easy, it should be run from a 9V battery and a
simple TL081 for example. The output could be adapted to a
multimeter, so there is a digital read-out.
I'm curious to see how it works...
73, Stefan
|
