From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: LF: A transductor instead of a traditional variometer on
 VLF/LF/MF? Done!
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Date: Sun, 15 May 2016 18:55:07 +0000
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Subject: Re: LF: A transductor instead of a traditional variometer on
 VLF/LF/MF? Done!
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Hello Stefan,

very interesting.
The first question that comes to my mind: what is the Q factor of your "electric variometer" ?

73, Rik  ON7YD - OR7T

________________________________________
Van: owner-rsgb_lf_group@blacksheep.org <owner-rsgb_lf_group@blacksheep.org> namens DK7FC <selberdenken@posteo.de>
Verzonden: zondag 15 mei 2016 13:25
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: A transductor instead of a traditional variometer on VLF/LF/MF? Done!

Hi all,

I have built such a transductor today. It is intended for VLF resonance
adjustment but it will work on LF and MF and HF too, i bet.

Can someone of the LF and MF TX stations try that please? I think it is
the most comfortable way to realise a steerable 'variometer' without
mechanical components.

Now, i took 4 of my 100 cores of the 3C85 ferrite. Each one has an Al of
4 uH.

First i wound an AC winding with 22 turns:
https://dl.dropboxusercontent.com/u/19882028/VLF/Transductor%20AC%20winding.jpg

At 5170 Hz and 0.3A, this is the number of turns to prevent the core
from saturation. For the AC winding, the cores are in series, so the Al
= 16 uH. With 22 turns and Al = 16 uH, L = 7.74 mH.

Then i added a winding for DC. For saturating the cores with a DC field,
I * N is constant, so i took a thin wire and many turns because it is
easier to generate 0.5A at 5V then 10A at 0.25V :-)
For the DC winding, N = 20. There is still room for another 20 turns but
this is a first test. The DC winding must be wound anti-serial! Actually
it is a ferrite transformer and you will short cut the transformed AC
voltage that appears on the DC winding. So you need to wind two windings
on a half of the construction and switch them anti-serial, so the AC
voltage is compensated but the cores can still be saturated by the DC
current.
https://dl.dropboxusercontent.com/u/19882028/VLF/Transductor%20ACDC%20winding.jpg
While winding the DC winding, you need to listen to ACDC, whether you
want to or not!

For a test, i build a resonance circuit (
https://dl.dropboxusercontent.com/u/19882028/VLF/Transductor%20test%20arrangement.jpg
) and measured the resonance frequency as a function of the DC current:
C= 33 nF

I [A]    |    f res [kHz]       |    L [uH]    | relative L [%]
-------------------------------------------------------
0        |    9.59                |    8346        |    100
0.25   |    18.88              |    2153        |     26
0.5     |    27.03              |    1050        |     13
0.75   |    35.66              |    604          |    7.2
1.0     |    44.1                |    395          |    4.7
1.25   |    52.03              |    284          |    3.4
1.5     |    59.8                |    215          |    2.6
1.75   |    67.0                |    171          |    2.0
2.0     |    73.9                |    141          |    1.7

BTW, in all measurement points, the wave form looked like a perfect sine
wave!
A graph is attached. Look at the linearity of the resonance frequency.

The only thing that is can't understand: If this is a known circuit, why
does no one of use it for LF and MF for an easy resonance tuning??????
This circuit in series with a fixed coil can give a variable resonance
just in the desired range, e.g. 135.7...137.8 kHz!

I will now double the number of turns for the DC winding and insert that
construction into my VLF system. I will let you know in which range i
can vary the resonance frequency. Most likely i will need 3 of these
circuits in series.

73, Stefan


Am 14.05.2016 21:16, schrieb Warren Ziegler:
> Hi Chris,
>       Yes some serious mechanical engineering involved!
> My good friend Marshall designs vlf antennas for the military and has
> worked on NAA.
> In fact Marshall worked with Dr. Wundt, the fellow who built the
> Goliath vlf antenna in Germany in WWII and was later brought to the
> U.S. in Operation Paperclip. Wundt did the original design for NAA.
>
> Great stories!
>
> 73 Warren
>
> On Sat, May 14, 2016 at 12:16 PM, Chris Wilson<chris@chriswilson.tv>  wrote:
>
>> Hello Warren,
>>
>> Saturday, May 14, 2016
>>
>> Fascinating stuff, thanks for posting that, shame there are no photos,
>> do you know where one might see some photographs of these giants?
>>
>>
>> Best regards,
>>   Chris  2E0ILY                          mailto:chris@chriswilson.tv
>>
>>
>>
>>
>>> Yes NAA uses a saturated core reactor:
>>> http://coldwar-c4i.net/VLF/design.html
>>>
>>
>>
>>>
>>
>>
>
>
>