Stefan,

 

Very nice work on identifying ULF core materials, and on transformer design, construction and testing. The transformer looks beautiful.

 

How long did it take to hand wind the 4000 turns?   

 

Does the Kapton tape partially fill the 0.15 mm gap (such as with 5 mil tape), or completely fill the 0.15 mm gap?

 

73,

 

Jim AA5BW

 

 

From: [email protected] [mailto:[email protected]] On Behalf Of DK7FC
Sent: Thursday, January 25, 2018 4:34 PM
To: [email protected]; Renato Romero
Subject: ULF: 20 mA carrier on 970 Hz

 

Hello dear friends of the Ultra Low Frequencies :-)

Since 21:05 UTC i'm running a carrier on 970.005 Hz.

With a lot of work i built a new ULF coil for 970 Hz. It's Q is just 11! For the next experiment, the target voltage is 12 kV, that means 36 mA antenna current and about 10 nW ERP!!
Since the Q of the coil is so low i decided to add a primary winding in this experiment, so actually it is a transformer now.
Here is an image showing the transformer inside the large waterproof PVC tube on the roof: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/ULF_coil_970Hz.jpg
The core material is that special stuff i bought a few months ago, see the old mail below. The iron cross section area is 40 mm x 40 mm. With acceptable upheating i can apply up to 4 V / turn, which means 0.4 T at 970 Hz. Not much but better than ferrite and it has quite a high mu r! Also i can form all wanted geometries, which is a bit hard when using ferrite :-)
On the core there are 4 windings which have 1000 (hand-wound!) turns each. So i could apply up to 16 kV. But in the coming experiment i stay at 3 V / turn.
The core is floating, so its potential against ground is given by the RC network of the geometry of the arrangement. I spent loads of Kapton tape which is just excellent for all such applications!
Oh, the iron core has two air gaps of course. It should be about 2x 0.15 mm. The Kapton tape realising the air gap also helps to isolate the two half cores from each other. This helps to reduce the E field stress.

I just made a frequency sweep and found that the actual resonance is near 1100 Hz. But the Q is low and the TX power is low too. The only disadvantage beeing outside the resonance should be a higher primary voltage and higher PA losses.

SpecLab and the antenna current regulator carefully holds the phase and target current! This is important here. A view into the box showing the PA, power supply, PA output transformer (yes, i'm still using N30 ferrite at 970 Hz!! But just 1 V / turn on a AL=10800 nH core), digital and analog antenna current measurement: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/[email protected]

I intend to run the carrier for a hour and then check the temperatures. Later i want o rise to 24 mA and check again....

More soon...

73, Stefan


Am 16.11.2017 18:24, schrieb DK7FC:

...today i drove to the company and got that high permeablic strip. http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/Powercore_H075-18_20mm_Thyssen.jpg
Quite a large amount!
To be continued...

73, Stefan

Am 13.11.2017 16:03, schrieb DK7FC:

Today i searched for suitable materials to build a iron band rod for a coil for 970 Hz.
I learned about kornorientiertes Elektroblech, https://de.wikipedia.org/wiki/Elektroblech or https://en.wikipedia.org/wiki/Electrical_steel
A normal 50 Hz transformer is using 0.5 mm plates. For higher frequencies there are thinner plates available.
I searched for a local company and quickly found this product catalogue:
http://www.lohse-ringbandkerne.de/uploads/downloads/Lohse%20Prospekt%20D_web_2017.pdf

Excellent! They offer 0.23 mm think plates.
Then i sent them an email request and later i had a telephone talk with the chief of the company. I asked if they have maybe even better materials and he said yes, they have a band of the type H075/18/20. This is a band which has a thickness of just 0.18 mm and it is 20 mm width. Since it is grain-oriented it matters how the B field passes through it.
He said that this special band is worse at 50 Hz but can be used to up to 4 kHz!!!!!!!!!!!!!!!!!!!!!!!!!!! So maybe this opens the frequency range from 4 kHz down to the lower ULF!!!! :-)

I got a good price, just 4 EUR for 1 kg but i have to order at least for 100 EUR so i will order 25 kg of that stuff! Already done!

My idea is to build a 0.5 m long rod. One piece of the band will then have a cross section area of  3.6 mm^2. I will need about 1000 to 1500 of these bands in parallel. This should fit into a PVC tube with an outher diameter of 80 mm. Very handy!

I'll keep you informed ;-)

73, Stefan