I understand your setup. It is not that hard to move.
I am not going to use such low VLF freq but as I mentioned am going for license to try get 28-30 kHz. Then I can run power up with less troubles of 8.9 kHz freq. It won't be till next season but am planning now for coil cover-coil size-etc. I have already 2' piece 18 inch white PVC pipe. Will wind 1000 meters #16 wire to start. I want to use my present 74 kHz coil inside as it is and add the extra coil outside then I can trim inside to hit exact resonance.
Date: Thu, 26 Dec 2013 19:44:09 +0100
From:
[email protected]To:
[email protected]Subject: Re: VLF: 8969.99
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
Date: Thu, 26 Dec 2013 18:32:43 +0100
From:
[email protected]
To:
[email protected]
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
Date: Thu, 26 Dec 2013 13:55:11 +0100
From:
[email protected]
To:
[email protected]
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
