hello Dimitris,
I don't have any experience on 475kHz, but some on 136kHz and HF.
I believe a PVC former is OK, if it's a pipe former, not a solid rod.
I made a dozen of 136kHz loading coils, with 165mm diameter PVC drain pipe and
325mm diameter polypropilene pipe, and got Qs of 300 to 340, at 9mH, 7.5kohm,
with wrapping wire of 0.51mm diameter copper and 0.15mm thin ETFE jacket,
rather thin wire. (copper-diameter/pitch ratio = 0.64)
240V electrical wire (with PVC jacket) sounds OK to me,
depending on the dimentions,
because it gives you spacing between adjacent copper,
to reduce eddy current loss.
copper-diameter/pitch ratio of 0.6 to 0.8 should be a good choice.
below 0.6 gives you too thin copper for the given space,
and above 0.8 no improvement was observed on my experiment,
wich agrees with the famous Medhurst's paper.
Litz wire should be good, (depending on dimentions and strand configuration),
if it has similar outer diameter as your 240V electrical wire.
JH1GVY suceeded to achieve Q=>1000, on 136kHz.
I saw your photo, and noted that you wound your wire with spacing in banks.
I think the spacing is not necessary, because you already have spacing
bewteen adjacent wire made by the PVC jacket, to reduce eddy-current.
Inter-wire capacitance is important between turns far away (end-to-end or
diagonal), not adjacent wires.
Basically, it's dictated primarily by the coil diameter,
secondary the coil length (small effet), and wire diameter spacing does not pl
ay roll.
This is proven also in Medhurst's paper, and my experiments convinced me.
Without bank spacing, you will have more inductuance with same numbers of turn
s,
or you can reduce turns and wire length for same inductance,
witch will give you less resistance ( a little though. 10% or so).
Good luck in your project,
I will be happy to hear your results.
73s, Hideho YAMAMURA, JF1DMQ/AA6VE
----- Original Message -----
>Date: Fri, 15 Feb 2013 11:52:04 +1100
>From: Dimitrios Tsifakis <[email protected]>
>To: [email protected]
>Subject: Re: LF: how to increase the Q of my loading coil?
>
>
>Hi Stefan,
>
>A photo of the coil can be seen here:
>
>http://people.physics.anu.edu.au/~dxt103/500/
>
>The operating position is inside a little metal garden shed. I have a
>wooden bench and it sits on that. There is maybe 0.5 m of space or
>more between the inductor and the shed walls.
>
>Ground losses are estimated to be a bit less than 20 ohm. This varies
>a bit with the WX, currently after a bit of rain think it is probably
>around 17 or 18 ohm. There is clay under the soil, which I think is
>good news when it comes to conductivity :-)
>
>Going from 27 ohm to say (Q=1000) about 20 ohm antenna impedance,
>would result in a small but very welcome antenna current increase...
>
>73, Dimitris
>
>
>2013/2/15 Stefan Sch?fer <[email protected]>:
>> Hi Dimitris,
>>
>> Do you have a photo showing the coil in its position?
>>
>> What are the ground losses, about? R coil = 9 Ohm with that Q and XL....
>> Litz wire helps of course, if you have enough...
>>
>> 73, Stefan/DK7FC
>>
>>
>> Am 15.02.2013 01:31, schrieb Dimitrios Tsifakis:
>>
>>> Hello group,
>>>
>>> I would like to increase the Q of my loading coil for 475 kHz. . It
>>> consists currently of a 20-litre plastic bucket with standard house
>>> 240V electrical wire (with PVC jacket). I measured the Q and found it
>>> to be about 220 (XL is about 2 kohm). I do have some Litz wire I can
>>> use. I also have a piece of large diameter (25 cm) storm water pipe,
>>> which I think is made of PVC. Would you recommend using a PVC former
>>> or should I look for a more exotic material (glass/porcelain)? Would
>>> you think the inter-turn capacitance is very detrimental and some
>>> exotic winding technique would yield better results?
>>>
>>> I understand that ground losses are bigger in my case than the
>>> inductor losses, but I would like to address the inductor first.
>>>
>>> 73, Dimitris VK1SV
>>>
>>
>>
>
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