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: [email protected] <[email protected]>
namens DK7FC <[email protected]>
Verzonden: zondag 15 mei 2016 13:25
Aan: [email protected]
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<[email protected]> 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:[email protected]
>>
>>
>>
>>
>>> Yes NAA uses a saturated core reactor:
>>> http://coldwar-c4i.net/VLF/design.html
>>>
>>
>>
>>>
>>
>>
>
>
>
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