Stefan,
Congrats on the ULF/QRP innovation and result!
I'm sure that your interest is in pushing the range but since your remote site
is 3.5km away I thought I'd mention something interesting about ranges less
than 10 km at 3 kHz or less.
For < 10 km at low VLF and ULF frequencies I use an inexpensive 2kW audio
amplifier, a single turn loop buried 3" - 6" in the soil (takes a couple of
hours to bury a sizeable loop in loose soil), and a (very small) 4x4 array of
PHE450 capacitors. With loop horizontal and buried the radiative field at a
wavelength or more is negligible, but at small fractional wavelengths: the
inductive field dominates and is relatively unabated by the soil, there are no
high voltage or weather issues, and the capacitors are electronically
switchable, which makes for some enjoyable experiments at shorter ranges
(results are consistent with the inductive field model, i.e. no substantial
drawbacks). In an environment where the loop can be inclined 20 degrees or so,
the radiative field is non-negligible which is interesting for longer ranges
but not generally practical.
Probably not useful for your purposes but makes for enjoyable experimentation,
and high quality frequency-agile local links.
73,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Wednesday, June 8, 2016 5:16 AM
To: [email protected]
Subject: ULF: A first step on the 100 km band
Hi all,
I've got a first result with my ULF project: One of the ideas to generate and
radiate a signal on the 100 km band to use a ferrite power transformer with
using two E cores out of N27 material. These are available at
https://www.buerklin.com/de/e-kern/p/83d970
At 2970 Hz i can apply 1 V / turn without saturating the core, maybe even more.
I think i can generate 3 kV (rms) with one transformer without a risk of a
flashover. And i can set an air gap between the two E cores.
For 2970 Hz i need L = 6.1 H! Now without an air gap i need about 800 turns
(hand wound!)to resonate the antenna. So i can apply 800 V now.
On 2970 Hz, my antenna radiation resistance is 70 uOhm. With 800V on the wire
it radiates 6 nW!
The distance to my remote site is 3.5 km or 0.035 lambda.
I'm TXing since last night and got a trace of up to 15 dB SNR in 424 uHz. Quite
weak but it's a first step.
The signal was radiated with an E field antenna and received with a H field
antenna, so there could be a better result in the near field.
I' now planning to wind more turns on the transformer and add an air gap to
keep the inductance and rise the voltage limit.
73, Stefan
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