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Date: Tue, 2 Dec 2014 09:12:47 +1100
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From: Dimitrios Tsifakis <dtsifakis@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: ELF communications ?
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Hi Stefan,

it's always worth giving it a try! There are people that use toroid
power transformers as valve/tube output transformers. So don't
disregard them for audio use! I agree that the efficiency may be a bit
lower but I can tell you, I have tested half a dozen of them and I
have found that there is one that has an almost flat response up to 20
kHz! Others are not so good. I used as a load what I think my antenna
is: some resistance (ground loss) and some capacitance in series. Now
I have to see how much power for how much time they can handle.

Also there is a nice large modulation transformer that I could use
too. Indeed, summer is the time for some field work of this nature!

73, Dimitris VK1SV


2014-12-02 7:32 GMT+11:00 DK7FC <73dk7fc@googlemail.com>:
> Hi Dimitris,
>
> Well, i have had 2 of these HV transformers. The first one got an internal
> fault during the experiments. A few weeks later i took the second one and
> wanted to repeat the experiment but i found that it was shorted from the
> beginning on.
> BUT, last friday we bought another HV transformer of a similar type for an
> application at work. This one even generates 18 kV and 40 mA! I will repeat
> the experiment then.
>
> Regarding VLF, i do not think that one can get 100% or even 30% of the rated
> voltage at frequencies above a few 100 Hz. The stray-C of the secondary
> turns is much to high. Also the core of the transformer will not work at a
> few kHz. For a 10 kV transformer i would guess and expect 5 kV at 500 Hz
> when using a high resistive load.
>
> But just give it a try.
>
> Aaah, i understand, it is summer in VK and you want to go out in the field,
> trying a ground dipole, 2x 10 km? :-)
>
> 73, Stefan/DK7FC
>
> Am 01.12.2014 21:19, schrieb Dimitrios Tsifakis:
>
>> Hi Stefan,
>>
>>
>>>
>>> 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
>>>
>>
>> Have you done any more tests with this? I am curious to see the
>> results. Would this idea work on VLF as well? I have come across some
>> power toroid transformers that have a reasonablywide useful bandwidth
>> that extends in the VLF part of the spectrum and perhaps such a
>> transformer connected to a really nice amateur LF/MF antenna could be
>> a very quick way of getting a small signal on VLF?
>>
>> 73, DImitris VK1SV
>>
>>
>
>