Re: ULF: 36 mA carrier on 970 Hz

[DK7FC <selberdenken@posteo.de>]

...the carrier still runs at 36 mA. It confirms that the construction actually holds the 12 kV permanently. Also the upwarming seems to be no problem. I will stop the carrier at 0 UTC and prepare the next /p experiment....

73, Stefan

Am 28.01.2018 01:11, schrieb DK7FC:

ULF,

I managed to pull the resonance a bit down by adding 120 turns to the coil and reducing the air gap a little more. The resonance is now quite close to 970 Hz.

The carrier on 970.005 is now running at 36 mA antenna current since 23:50 UTC. That's the 10 nW ERP level.

Also i added more turns prim and sec on the N30 ferrite transformer. On this blue core i'm now running up to 0.3 V/turn.

The iron core will now heat up and i hope the temperatures are not critical. By adjusting the resonance and reducing the flux in the ferre transformer the power supply runs at 25V/3.6A now, just like yesterday when i run 20 mA, so the efficiency has improved a lot.
Now the supply current limit is set to 4.5 A and the antenna current safety limit set to 3 mA (i.e. stops at < 33 mA).
Let's hope the system passes the test and runs throughout the night :-)
Now, 4 dB more than last night and 7.6 dB more than in my last /p experiment...

73, Stefan

PS: The tree is back and a trace is shown on the grabber, http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html



Am 27.01.2018 18:01, schrieb DK7FC:

...the carrier has been on the air since the announced time below. Inbetween i increased the level to 24 mA (8 kV). Now at 17 UTC the carrier will stop. I'll do some work to tune to the resonance more carefully. It will come back in some hours then...

73, Stefan

Am 25.01.2018 22:33, schrieb DK7FC:

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/20mA@970Hz.jpg

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