Re: LF: ELF communications ?

[DK1IS <DK1IS@kabelmail.de>]

Hi Stefan,

interesting stuff! Keep in mind these oil burner ignition transformers are designed to feed a spark with high ignition but low burning voltage - nearly short circuit. So they have a large stray inductance and resistance and a current limiting characteristc. Furthermore they are only suitable for intermittend service (33% within 3 minutes as you see from the label) and the middle of the secondary is usually connected to the case. I used 6 of them in parallel for feeding a tesla-transformer built by students during my former job at FH Amberg. But you shold try it anyway.

Nice your high power capacitor battery - reminds me to an own project during my promotion at TU Braunschweig in the 70s of last century ;-). Our institute made R+D on arcs and sparks and built a synthetic switch testing facility for medium voltage vacuum switches. Before breaking an LC circuit made a current of 50 kA for two halfwaves of 50 Hz and after breaking there was a recovering voltage abot 60 kV at some kHz. Dont know the components data anymore but there was a lot of stored energy and we had to develop special fuses for each capacitor to avoid explosions in case of a component failure. At that time I devloped the central electronic control unit for the whole testing site - some severe emc problems had to be solved successfully! Later on the had a lot of trouble substituting all those large PCB filled capacitors ...  Verdammt lang her, verdammt lang her!

Wishing you good results with your test!

73,
Tom, DK1IS
www.qrz.com/db/dk1is


Am 09.10.2014 22:57, schrieb DK7FC:

Hi Markus,

Thanks for the calculations. We will see the results.
I do take care. In my promotion project at TU Darmstadt i daily worked with a capacitor battery having 15 kV / 12000 uF, see an image showing 1/3 of the battery at https://dl.dropboxusercontent.com/u/19882028/IMG_8073.JPG Would be fine for a tube PA ! :-)

Once again the PA has some EMC problems and i cannot run the full power. Hope to fix that tonite...

73, Stefan


Am 09.10.2014 18:35, schrieb Markus Vester:

Stefan,

 

this could work. In the capacitive near-field range, the electrical field would be

 

 E = voltage * capacitance * effective height / (2 pi epsilon0) / distance ^3

 

With 10 kV on your antenna capacitance and height, you'd get about 0.15 mV/m at 2.4 km, maybe 14 dB stronger than ZEVS.

 

Take care! Touching 10 kV on 136 kHz will severly burn you. But on 136 Hz it would kill you, unless the current is safely limited to a few mA. 

 

73, Markus

-----Ursprüngliche Mitteilung-----
Von: DK7FC <73dk7fc@googlemail..com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 9 Okt 2014 2:51 pm
Betreff: LF: ELF communications ?

Hi ELF, 

  

 This afternoon i'm attempting to transmit on my INV-L on 136.172 Hz (not  

 kHz!). Just preparing my H bridge VLF PA and i intend to use an old 10  

 kV transformer which i got from an old furnance (to inflame the oil  

 stream), see  

 https://dl.dropboxusercontent.com/u/19882028/VLF/10kV%20Trafo.jpg 

  

 Will that work on 2.4 km distance? It's well inside the near field.  

 Which mode could be possible? QRSS-3? CW? 

 The 2200000 m band, or 2.2 Mm band :-) A near field of 350 km !! 

 I hope i can apply 10 kV to the antenna. It will not be resonated. And  

 maybe i will see harmonics as well, because the input is rectangular... 

  

 73, Stefan/DK7FC