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Date: Sun, 17 Apr 2016 00:30:03 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: TXing on VLF again, Iron powder cores...
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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: owner-rsgb_lf_group@blacksheep.org
>> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
>> Sent: Friday, April 15, 2016 10:00 PM
>> To: rsgb_lf_group@blacksheep.org
>> 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 :-)
>>
>>
>>      
>
>