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Re: LF: ELF communications ?

To: [email protected]
Subject: Re: LF: ELF communications ?
From: DK7FC <[email protected]>
Date: Fri, 10 Oct 2014 14:14:01 +0200
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Hi Tom,

Am 10.10.2014 12:15, schrieb DK1IS:
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.
As i was 17 years old, i used 3 of them in series :-) In series on the secondary side, in parallel on the primary side. About 3cm long permanent flash over. But just for one minute, then the insulation barrier on one transformer broke down between secondary and primary.
Well, now i just use one HV output wire and ground / housing, i.e. just 5 kV in a first test. On 136 Hz, the 470 pF antenna is not a heavy load. However there may be resonance effects. I will check the antenna voltage waveform by using an electric probe on the scope. But first i have to solve the EMC problems of the PA....
Will report later.

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.
A synthetic test circuit for medium voltage vacuum circuit breakers, exactly this is what my project and lab dealt with. We also got 50 kA (peak), 35 kA rms.
Dont know the components data anymore but there was a lot of stored energy
1.35 MJ in that circuit.
and we had to develop special fuses for each capacitor to avoid explosions in case of a component failure.
We didn't use fuses, and there were failures! ;-) But fortunately the energy is limited. Many stories to tell. BTW i built the charge unit for that capacitor from a 20 kV/ 220V / 20 kVA transformer, inverse switched. Charging to 15 kV took about 4 minutes. The current of the single phase 230V side of the transformer was 160A when charging begun :-)
Energietechnik, that's it!!!!
So you see, that small 10 kV transformer is just a game. Anyway i know the risks of course.
But we're coming OT ;-)

At that time I devloped the central electronic control unit for the whole testing site - some severe emc problems had to be solved successfully!
Was my job as well. Solved by using many fiber optic cables, at least for some problems.
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!
Tnx, 73, Stefan

PS: We need to continue discussing in a longer MF CW QSO i would suggest!!!

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