Just a thought
Have you thought about Scan coils cores?
Regards
Lawrence
On 4/29/16, DK7FC <[email protected]> wrote:
> Hi Rik,
>
> the experiment with 5 cores has shown that the iron powder cores are not
> so efficient at a low l/d. But of course they help a bit, like seen in
> the current transmit coil configuration that i use.
> I'm going to order the 3C-85 ferrites and continue with the experiments.
> These high ur ferrites are useful for several applications anyway..
>
> 73, Stefan
>
> Am 28.04.2016 22:23, schrieb Rik Strobbe:
>>
>> Hi Stefan,
>>
>> what about a "fatter" (length/diameter = 1) coil filled with some core
>> stacks in parallel?
>>
>> For a slim coil (large length/diameter ratio) the inductance is more
>> or less proportional to the number of windings while for a fat coil
>> inductance is more or less proportional to the square of the number of
>> windings.
>>
>> But I don't know how effective the cores will be in such a fat coil.
>>
>> 73, Rik ON7YD - OR7T
>>
>> ------------------------------------------------------------------------
>> *Van:* [email protected]
>> <[email protected]> namens DK7FC
>> <[email protected]>
>> *Verzonden:* donderdag 28 april 2016 20:34
>> *Aan:* [email protected]
>> *Onderwerp:* Re: VLF: T106-52 cores on VLF, continued, thoughts...
>> OK, after a break in the sunset i thought:
>> If 皴 tends to 6.5 and L/l to 22 mH/m for 0.5mm wire for l ->
>> infinity, and if i want to keep the coil length at 0.8m, which would
>> be 17.6 mH for 0.5mm wire. However i need 788 mH! So i need a 6.7
>> times smaller wire, i.e. 0.074mm diameter. This is impossible and i
>> wouldn't carry the antenna current.
>> A new coil would only make sense if i can rise the signal by at least
>> 6 dB. I just measured 260 mA. So let's say 600 mA would be fine. And i
>> like the 0.4mm wire and would like to use that.
>> In the moment i see no chance for a single layer coil using this
>> technique :-(
>>
>> 73, Stefan
>>
>> Am 28.04.2016 20:02, schrieb DK7FC:
>>> Hmm, well, ok, after some discussions, the show ehm the experiments
>>> must go on.
>>>
>>> I'm continuing with a higher l/d ratio. 13 of these cores are
>>> available, the other ones are parts of my transmit coil now. I like
>>> to get 3 measurements to approximate a curve showing L/l and 皴(eff)
>>> over the ratio l/d. So a useful number of cores is 5 (already done,
>>> see below), 9 and 13.
>>>
>>> *_5 core stack (yesterdays measurement):_*
>>> The ratio coil diameter / coil length, *l/d = 49/33 = 1.48*.
>>> Effective *皴 = 3.75*
>>> L/l = 452 焙 / 49 mm = *9.22 mH/m*
>>>
>>> *_9 core stack:_*
>>> As a resonance C i use 0.3 uF (measured C = 306 nF)
>>> The resonance is at 7.26 kHz. The bandwidth is (7.36 - 7.18) kHz =
>>> 180 Hz. Q = 40. L = 1.75 mH
>>> Without the cores inside, the resonance is found at f = 17.1 kHz. BW
>>> is (17.6 - 16.69) kHz = 1.05 kHz. Q = 16.8. L = 283 焙.
>>> https://dl.dropboxusercontent.com/u/19882028/VLF/9%20cores.jpg
>>> *l/d = 96/33 = 2.91*
>>> So now the effective *皴 is 6.18*
>>> L/l = 1.75 mH / 96 mm = *18.23 mH/m*
>>> L/l (9) / L/l (5) = 1.98
>>>
>>> _*13 core stack:*_
>>> C= 202 nF
>>> Resonance (with cores) at 6.485 kHz. BW = (6.56 - 6.42) kHz = 140 Hz.
>>> Q = 46. L = 2.98 mH
>>> https://dl.dropboxusercontent.com/u/19882028/VLF/13cores.jpg
>>> Resonance (without cores) at 16.78 kHz. BW = (17.26 - 16.38) kHz =
>>> 880 Hz. Q = 19. L = 445 焙.
>>> *l/d = 145/33 = 4.39*
>>> The effective *皴 = 6.70*
>>> L/l = 2.98 mH / 145 mm = *20.55 mH/m*
>>>
>>> OK, now, this tends to a certain value for L/l, maybe 22 mH/m (see
>>> attachment) for a 0.5mm diameter wire. Hmm, so my coil would be just
>>> 35m high, about as high as the feed point of the antenna :-)
>>> So a thinner wire is needed or a tube with 3 or more cores in parallel.
>>> More soon...
>>>
>>> 73, Stefan
>>>
>>>
>>> Am 27.04.2016 20:20, schrieb DK7FC:
>>>> Hi VLF,
>>>>
>>>> I've done a quick experiment with the T106-52 cores which could give
>>>> some more ideas regarding these cores for a compact VLF coil.
>>>>
>>>> I wound a coil with 0.5mm enameled cu wire, 85 turns at 33mm
>>>> diameter. Inside the coil there are 5 of these cores stacked on
>>>> another. In parallel there is a suitable C of 1 uF.
>>>> https://dl.dropboxusercontent.com/u/19882028/VLF/20160427_195530.jpg
>>>>
>>>> The resonance was found at 7.49 kHz. The 3 dB bandwidth is
>>>> (7.64-7.36) kHz = 280 Hz. Q = 27. L = 452 uH.
>>>> Without the cores inside, the resonance frequency rises to 14.54 kHz
>>>> and the bandwidth is (15.12-14.07) kHz = 1.05 kHz. Q = 14. L = 120 uH.
>>>>
>>>> Hmm, so in this configuration, the *effective 皴 (ur) seems to be
>>>> just 3.75*! :-/
>>>> That means i still need half of the number of turns for a single
>>>> layer VLF transmit coil?!?
>>>>
>>>> 73, Stefan
>>>>
>
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