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Re: LF: A transductor instead of a traditional variometer on VLF/LF/MF?

To: [email protected]
Subject: Re: LF: A transductor instead of a traditional variometer on VLF/LF/MF? Done!
From: Wolfgang Büscher <[email protected]>
Date: Sun, 15 May 2016 14:12:49 +0200
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Greetings all,

Interesting application .. but wouldn't the operation of such a simple transductor (wound on a single ferrite core) depend a lot on the 'RF drive' itself, and / or have different influence on the positive and negative half wave ? Transductors for mains frequencies (as used in Theaters for electric lighting, long before the semiconductor age) used a balanced configuration, so the satturation appeared symmetric for both half waves. I think the Alexanderson alternator at Grimeton uses a similar principle for the modulator (keying). So for a high-power application, one would possibly need two ferrite rings, RF coils "anti-parallel" (with opposite DC magnetisation).
73,
   Wolf DL4YHF
(p.s. had to go qrt yesterday during the QSO with Vinny, there was something wrong with the TX on this end which needs further examination. Hope you had fun there on the /p site, and better wx conditions. There was a lot of QRN here.)

Am 15.05.2016 um 13:25 schrieb DK7FC:
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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