>I had the idea to replace them by iron powder cores, T106-25 types. I 

There's a typo: 25 should read 52.
Really cheap cores.
The question is:
Are they iron powder or ferrite like the seller says?
According to the spec'd AL value they should be iron powder.
Did you *measure* AL? 

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 :-)
>
>