Hi Jim,
Tnx for the contribution. Yes, sure, experiments in the near field range
are mostly easy. In fact i want to add a few 10 dB more signal level
later. It was just a first step to get a very first impression. The
transformer is back on my desk here and i added a small air gap to the
ferrite E cores now. This rose the resonance frequency from 3.1 kHz to
4.92 kHz. Now i can add more turns to come back to 2.97 kHz again. Then
i can run a higher voltage. Belive me, i didn't calculate to much. I
just like winding transformer and listening good music during that time,
just like an old house wife knits socks and doesn't know who will weak
them later ;-) But of course i need to know some parameters.
The wire diameter is just 0.22 mm, so the complete stack will not handle
several 100 mA antenna current. But i will see what i can get.
My antenna holds 40 kV (rms) during rain, so there is some room left :-)
More precisely: +34 dB or 15 uW ERP could be possible. At 40 kV the
antenna current would be 350 mA. I would need 0.4mm wire for that. And
12 transformers in series!
The QRN on ULF / 100 km band is much lower than on 8.27 or 6.47 kHz. But
the receiver must be in a very quiet location, only the 'best' RX stns
could have a chance to be successful. But there are some in a range
below 1000 km here! :-)
So maybe there are certain advantages?!
Before i can ask Paul to try to search for a peak from a one week
carrier transmission i have to add some dBs :-)
More soon...
73, Stefan
Am 08.06.2016 15:32, schrieb [email protected]:
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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