Re: LF: VLF in Canada

[Markus Vester <markusvester@aol.com>]

> If you cut the bottoms out from the buckets...

... already done: http://df6nm.bplaced.net/VLF/pictures/coil_opened_for_airflow.jpg

Actually thought of putting a fan on the top and feed it inductively, but not sure how the motor electronics would handle the fields.

 

> I could not get to the arced coil .JPG

You should be able to browse the folder http://df6nm.bplaced.net/VLF/pictures/ - seems to work from here. 

 

The flashover had happened a couple of weeks ago during a long unattended transmission. The buckets had been pushed all the way in to bring the resonance from 8.97 to 8.27 kHz, in a silly attempt to protect the Euclid lightning locator network against undue interference from my superstrong microwatts (ha ha). In the meantime, I have repaired the faulty coil, increased the antenna capacitance a bit by doubling up some more parts of the antenna wire, and inserted a few fat chunks of ferrite in the coil (more pics in above directory). So I'm back to "safe 4-Lego spacing" at the new frequency (at least I think so ;-)

 

73,

Markus

 

-----Ursprüngliche Mitteilung----- 
Von: stan, W1LE <stanw1le@verizon.net>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Di, 24 Jun 2014 3:12 pm
Betreff: Re: LF: VLF in Canada

Hello Markus,

Interesting post about your coil.
If you cut the bottoms out from the buckets,
would you have better convective air flow for cooling the coils ?
Like a chimney effect.

I am starting to think about 9KHz operations. An interesting challenge.

I could not get to the arced coil .JPG. Do you have a better web address ?

Stan, W1LE    Cape Cod   FN41sr



On 24-Jun-14 6:55 AM, Markus Vester wrote:

Joe, good to read this!

 

Regarding the loading coil, I would agree with Stefan that a large multiturn air coil is the best option. A laminated iron core would suffer from excessive eddy current losses, and the effect of ferrites is limited by saturation and hysteresis losses.

 

My 1.3 henry coil consumed 2.3 km of 0.4 mm enameled wire, using 7 buckets with 480 turns on each:
df6nm.bplaced.net/VLF/VLF_110304-06/coil_legospacers.jpg.
The advantage is that due to magnetic coupling between layers, you will need less wire for a given inductance. And the inductance is adjustable across a wide range, using spacers. Disadvantages are the high electric field between layers limiting voltage capability, and less effective heat removal from the inner buckets. Stuffing the buckets too tightly into one another is surely not a good idea:
df6nm.bplaced.net/VLF/pictures/arced_coil_140601.jpg