|Subject:||Re: LF: TXing on VLF again, Iron powder cores... broomstick coil?|
|From:||Markus Vester <[email protected]>|
|Date:||Sun, 17 Apr 2016 07:56:32 -0400|
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The supplier states AL = 95 nH for the T106 toroids. From the geometry (Do=27, Di=14, h=11.5 mm), we can calculate magnetic circumference lt = pi*(27+14)/2 mm = 62.4 mm and cross section at = 11.5*14 mm^2 = 161 mm^2. Using
AL = µr * µ0 * at / lt
we get µr = 95nH / 3.14nH = 30. This low value indicates that the cores indeed consist of iron powder rather then ferrite material.
My original idea was to assemble a thin "broomstick" coil around a lr = 1 m long stack of ~ 90 cores, surrounded by a single-layer solonoid of n = 5000 turns (0.2 mm wire) and 3 cm diameter. The core cross section of the rod is then
ar = pi/4 * (Do-Di)^2 = 4 cm^2,
which at 8.27 kHz would allow 4.1 V per turn at 0.2 Tesla flux.
We have to consider the effect of the air gaps due to the enameled cores. Assuming a gap 2 * 0.05 mm every 11.5 mm we get µgap = 11.5/0.1 = 115. Due to the rod's large length-to-diameter ratio, the influence of the demagnetisation factor µd ~ lr^2 / ar = 5000 is negligible, and we get
µreff = 1/(1/µr + 1/µgap + 1/µd) = 1 / (1/30 + 1/115 + 1/5000) = 24.
and a total inductance
L = µreff * µ0 * ar / lr * n^2 = 12 nH * n^2 = 0.3 Henry.
Unfortunately this is much less than the 1.4 Henry required to resonate my small 270 pF antenna at 8.27 kHz, so the coil would need to be either thicker or much longer.
Anyway I have ordered some cores to make measurements, and also some of the red double-height ferrite (?) sleeves from the same supplier.
All the best,
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: So, 17 Apr 2016 12:31 am
Betreff: Re: LF: TXing on VLF again, Iron powder cores...
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