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Date: Thu, 09 Jun 2016 22:26:43 +0200
From: DK7FC <selberdenken@posteo.de>
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To: rsgb_lf_group@blacksheep.org
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Subject: VLF: VLF loading coils for everyone?!?
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Status: O

Hi all,

I'm trying various VLF coil configuration in the last weeks, as you 
probably know.

The difficulty is to get a coil which handles the voltage, the current 
(or heat or losses). It has to provide the necessary L. Saturation of 
electrical conducting ferrite or iron powder materials must be avoided. 
The arrangement should be not to expensive and should have a low weight. 
It should be as compact as possible...

The latest and not yet tried idea is to use a stacked, air cored, 
multi-layer coil on a single PVC tube. Think about the LOPT 
transformers, they have many layers of turns which are isolated by a 
thin plastic foil.
Now the idea is to use a single 0.25 m diameter tube and 0.4mm wire, i 
ordered 2 kg wire today! I would then wind a layer of 35mm and use 50mm 
thin bonding tape to isolate it from the next one. Then i wind the wire 
back, a second layer. In the end i could wind 5 or 7 layers. This should 
give a certain inductance. I have not yet calculated its value.
If the goal is to get a stronger signal on 8270 Hz, i would for example 
need 600 mA antenna current which should be possible with such a coil, 
unless i don't need to many layers. 600 mA would cause about 25 kV (rms) 
on the antenna.

The next step is to wind a second and later a third 35mm stack in a 
distance of 20mm on the same tube. Each stack should handle 5 kV. With 8 
stacks in series i could handle 40 kV on 2970 Hz. When transmitting on 
8270 Hz, i could switch 2 x 4 stacks in parallel, then i have 1/4 of the 
inductance and i can run 2 times as much antenna current. Variations of 
the coupling and different combinations of stacks could realise a 
resonance on many frequencies.

Not sure if this was a good explanation. In a few days i will start 
winding first layers and will show some photos...

73, Stefan