Re: VLF: 8969.99

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hi Bob,

Oh, you're planning to become QRV on VLF, great!
What inductance will you need for your system? What coil diameter and wire diameter will you use? It is important to calculate the dimension of that coil before you start to wind it. A diameter of at least 60cm is to be recommended, better 80cm. But of course it depends on the wire diameter and isolation (or insulation?). If you just use a coil body that is on hand and start winding, you may find the residual L is much to low and then you come out with 3 coils in series which will be a huge construction in very inefficient. You should also leave some distance to ground, to prevent losses into the soil. A distance equal to the coil diameter is fine.
How will you manage the high voltages on the antenna? You will have to manage 50 kV rms or so.

For me, the situation is not as easy. I must not leave the coil its position permanenty. I have to remove it after the experiment. But that's not so dramatic. I can leave it into the building and we have an elevator...
Keep us informed by some photos :-)

73, Stefan/DK7FC


Am 26.12.2013 18:58, schrieb Bob Raide:

Stefan;
If I go to VLF I am going to add to my existing inductance outside.  I plan to make a box using "plexiglass" quarter inch thick with glued seams so is weather proof.  It will be clear [no color] and is very good dielectric.  I was going to ask you how much clearance I need and 30 cm is about 1 foot or 12 inches clearance around the coil.  Leave air gap around bottom so air can circulate so you don't build up moisture.  Small muffin fan with shroud to pull fresh air up and around coil and out.
Could even use clear vinyl material .025 thick and a clear vinyl box over a plastic pipe frame would be cheaper.  Clear vinyl used for side curtains on boats-etc.
I am in sewing business [make boat and truck covers] so could make you cover and you build the frame-I ship clear vinyl cover UPS to you or you could have local canvas company make it.  Use "RTV" over stitches to make water tight-Bob
 

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Date: Thu, 26 Dec 2013 18:32:43 +0100
From: Stefan.Schaefer@iup.uni-heidelberg.de
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: 8969.99

Hi Bob,

Of course, if the coil is protected against rain, then it is no problem. But the coil is quite large and due to the high voltage, the housing should ideally have a distance of 30cm or more to the coil. So the housing must be quite large, even more. And that makes it dangerous because of wind blasts on the to of the building in 35m AGL...
Anyway it would be nice and i also thought about using a simple foil across the coil, without additional distance.
However on LF, there are partial discharges on the top of the coil which burns holes into the protecting foil. And the VLF winding is 2000m long. It is a lot of effort to repair it after a short cut between some turns due to arcing. So it is a high risk.
I think i will make a test in the near future and see if 9 kHz partial discharges are as agressive as 137 kHz partial discharges :-)
73, Stefan/DK7FC

Am 26.12.2013 16:32, schrieb Bob Raide:

Stefan;
Even if you have your coils in weather proof housing rain is no good to transmit on 9 kHz? Bob
 

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Date: Thu, 26 Dec 2013 13:55:11 +0100
From: Stefan.Schaefer@iup.uni-heidelberg.de
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: 8969.99

Hi Uwe, Tom, VLF,

Best signal ever from Tom, capture attached. Is it due to the propagation or did it improve your signal?
What about some tests in OPDS32 or maybe JT9-30? Unfortunately there is permanent rain here so i have to wait some days longer.

73, Stefan/DK7FC