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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: Sat, 16 Apr 2016 20:53:14 +0200
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Hi Luis,

Am 16.04.2016 10:29, schrieb VIGILANT Luis Fernández:
Thank you very much for sharing you expertise on Yougurt manufacturing 
techniques ;-)

The pictures help a lot to get a clear idea of the coil. From earlier 
descriptions read here I had
a different picture (as scaring as the real one, anyway) of "the thing"
Thanks for the feedback.

My idea for VLF coil was to use a big bucket (1m deep by 50cm big diameter) 
covering the LF
coill.
A big bucket as you describe is, so far (!), the preferred and traditional way to go. It has advantages to the system i'm using now: It (a large single layer coil) holds higher voltages. It allows more power loss because it has a higher surface. But it is large and so it is not very mobile and not easy to cover from rain. Also it needs a higher position above ground to avoid further losses. But with 0.4 mm diameter wire you can easily run 1A antenna current 'key down'. When running some CW tests on my large coil on the 300m kite vertical, i run 1.8 A rms pulsed power (CW, you know...). This was possible because i switched 10x6000uF/350V in parallel to my small generator and the PA :-)
As i wrote, there are a few parameters to be optimised for your
situation and goals.
Some questions:
Which is the wire diameter you use ?
This small coil (actually wound by DF6NM) has 0.2mm diameter.
My large coil (qrz.com) has 0.4mm diameter. I rather recommend 0.4mm.

Which is the voltage you get in the last coil with the actual current ?
My antenna has 470 pF, so this is 40.8 kOhm at 8.27 kHz, i.e. i'm getting about 9 kV with 0.2A. My new goal with the latest coil configuration is 0.28 A, i.e. 3 dB more ERP and about 13 kV. BTW i did a 20 minute 0.28A test last night at 250V/50 Hz. The coild did not become to warm at that current level. 13 kV is really not much for VLF! 30 kV or 40 kV are normal values for VLF Dreamers (there is a certain anecdote to tell about the name 'Dreamers Band' :-) ).
NOTE: 470 pF! Your construction on the roof will have much less i bet.
You can calculate it. If you want to start on VLF, i strongly recommend
the try somehow to install a wire running to the other building, the top
of the other building! :-) You can connect it in series with a
non-conducting string to pull it back when a thunderstorm comes.
OR: Buy a kite and let it rise on the building, maybe only at night! Is
it possible? 100m on a 80m building? :-) I can advice you in any details :-)
Which size is 40% higer diameter ?
The current average diameter of this coil is 0.11m.

Should other pieces of iron instead of iron power rings work for this purpose ?
Probably not.
But maybe, thin (< 1mm diameter) vertical rods, isolated from each other? But then there will be a high capacitive coupling and dielectric problems. You would need a distance between upper turn (on HV) to that core which holds the HV. This is critical.
More and more i like the idea of what i built yesterday. Each of these
cores are conducting but they are coated! And further separated by the
hot glue. And further separated by the cups :-) So there is a certain E
field steering.
I understand that the coils you use now are single layer wound. Right ?
RR.
Later more from the current progress :-) I plan to come on air this night again...
73, Stefan

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