Hi Stefan,
Your sliding bucket VLF coil is making me envious. Markus uses this
method as well. I am using the pies configuration and limiting my current
to 1/4 amp to prevent high voltage problems.
After some tinkering I managed to get 1/3A with 2 large pies (~100mH) and
one small one. The total was 500mH at 150 ohm DC so very low loss,
but very difficult to find the shorted turns when it arcs out.
You are correct that winding VLF coils is relaxing. There is one motor
to twist the 24 0.08mm wires together and another to wind them on the
lexan spindles. The next step is to use 3 or 4 spindles and think about
how reduce the voltage gradients. It is relaxing watch this action. When
I get bored watching, I go in the back yard and work on aerials
for a while and check the winding later as it progresses.
You mentioned I should set a goal of 150 uW. The big RL is up again
and I'm looking out for cheap car audio amps so progress is being
made towards higher ERP.
Sadly it looks like the NEO7M I ordered in July will not be delivered
so we'll have to try again.
73 and keep up the amazing work Stefan
Joe
On Fri, 8 Sep 2017, DK7FC wrote:
Hi Joe,
Just as an inspiration for a VLF coil design, here's an image of the first
coil of a stackable set of coils for VLF:
http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/coil1.jpg
I just finished to wind it. It has *172 mH*. A 2nd and a 3rd and a 4th and
and and.. will be wound later. The advantage of that system is that i can
tune to any frequency, without steps. Also it is much easier to repair than
my large VLF coil for 2.97 kHz.
It uses 0.25 mm diameter wire and is intended to be driven at 300 mA antenna
current. The system will focus on frequencies < = 5.17 kHz.
It took about 7 hours for the winding and 2 hours for preparing a
construction to rotate it by a motor.
With that single coil i could resonate to 17.5 kHz. But with a second one i
will already be quite close to 8.27 kHz. With 4 of them i will already reach
5.17 kHz. And 6 of them could be fine for 2.97 kHz! Maybe i will build 8 of
them to reach 2.17 kHz :-)
The DC resistance of the single coil is 267 Ohm, so the losses will be 25 W
per coil. Ah and the coil diameter is 0.3 m (average).
The wire is hold in place by Kapton tape which is cheaply available from
Amazon.
73, Stefan
Am 07.09.2017 14:10, schrieb [email protected]:
This is amazing, Paul. To copy < 0.00001 watts across
the pond with the carrier drifting about is an amazing feat.
The daytime signal is used because more atmospheric
noise is propagated at night?
Unfortunately there is now a delay in getting the gps board but
better stability is certainly in the future.
Thank-you for your efforts and monitoring.
73
Joe VO1NA
On Thu, 7 Sep 2017, Paul Nicholson wrote:
Joe VO1NA wrote:
Today the aerial was disconnected at 0950 utc
Here's a non-coherent average over 8 days of 10:00 to 20:00
http://abelian.org/vlf/tmp/170907a.gif
Impossible to do coherent sum with this many days, without
GPS frequency lock.
Not bad for 8uW ERP but it should do a lot better with a precise
frequency.
--
Paul Nicholson
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