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Re: LF: TXing on VLF again, Iron powder cores...

To: [email protected]
Subject: Re: LF: TXing on VLF again, Iron powder cores...
From: DK7FC <[email protected]>
Date: Sun, 17 Apr 2016 00:30:03 +0200
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Hi Clemens,

Am 16.04.2016 21:42, schrieb Clemens Paul:
There's a typo: 25 should read 52.
Yes, sorry, a typo. It can also be read on the cores in my images ;-)
Really cheap cores.
Yes indeed! I called them and asked if they have 500 more of them available. They (she) said, they have MUCH more then 500 of them available :-)
The question is:
Are they iron powder or ferrite like the seller says?
The seller is wrong here.
T106 describes just the geometry of the core.
Material 52 can be 'read' from the colour combination.
According to the spec'd AL value they should be iron powder.
Did you *measure* AL?
No i didn't. I just observed how much the resonance frequency of my large coil and that small coil drops when i put them 'into the field'. This is what counts.
Markus did some calculations, maybe he will report you here.

73, Stefan
73
Clemens
DL4RAJ



-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Friday, April 15, 2016 10:00 PM
To: [email protected]
Subject: Re: LF: TXing on VLF again, Iron powder cores...

Hi VLF,

Today the improvements continued.
The goal was to replace the two ferrite rod moving side to
side into the
air flow channel in the center of the small VLF coil.
I had the idea to replace them by iron powder cores, T106-25 types. I
recently ordered 100 of them, they were quite cheap:
http://www.pollin.de/shop/dt/Mzk5OTQ3OTk-/Bauelemente_Bauteile/
Passive_Bauelemente/Spulen_Filter/Ferrit_Ringkern.html
There are 10 buckets stacked onto another. First i put 3 cores onto
every 2nd bucket, see
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_144048.jpg
This worked very well.
Next i got the idea to put more of them into the coil, 3 on
each bucket,
see
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_151736.jpg
That worked even better.
But the whole construction became heavier and sagged into itselfe.
So i put more and more cores into the coil, 2x 6 onto each bucket! See
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_15394
4.jpg and
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_155753.jpg
I hoped that i can spare one of the buckets to reduce the
overall losses
(= heating up) and reduce HV problems due to the higher stack, as well
as further reducing heating due to the higher surface of the
higher stack.
Indeed, in the end it was possible to remove 2 of 10 buckets!
That means i got some of the cores back and put them (3 onto another!)
where the highest upheating has to be expected,
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_163021.jpg

Now the is the current final construction for today,
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_202640.jpg

The weight of the coil is about 3 kg now :-)

I can see now that the Q of the coil is much higher. In a
transmit test
i measured a 3 dB BW of 180 Hz. With my 470 pF antenna the L
is 788 mH.
So Q is 46 and the overall R (=loss) is about 890 Ohm, if my
calculations are correct :-)

I hope to be able to run more power and current now. 250 mA is
hopefully
possible. That is a 2 dB improvement...

73, Stefan

PS: It would be interesting to go on playing the game: Using a bucket
with 40% higher diameter, also using twice the number of cores. This
would end up at a higher necessary stack distance (lower coupling) and
will sometime end up with a single layer coil! There will be a
compromise between: Size, max. power, max. voltage, losses, wire
diameter, weight, costs :-)

I can recommend the idea to those who plan to build a VLF TX coil :-)







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