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Date: Wed, 08 Jun 2016 17:47:16 +0200
From: DK7FC <selberdenken@posteo.de>
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References: <1685128417.20160531153441@chriswilson.tv> <CAHAQVWNRW8KmN01VfnPEFNHGSUyZgsqXqZT7d+2d=hMRm45TeA@mail.gmail.com> <844647135.20160607150703@chriswilson.tv> <5757E24F.1050507@posteo.de> <023701d1c18a$39660550$ac320ff0$@comcast.net>
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Subject: Re: U LF: RE: A first step on the 100 km band
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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 hvanesce@comcast.net:
> 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: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
> Sent: Wednesday, June 8, 2016 5:16 AM
> To: rsgb_lf_group@blacksheep.org
> 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
>
>
>