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Date: Thu, 20 Dec 2018 19:04:02 +0100
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: Rogowski-coils for RF measurements, into the field...
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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
>>>>