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30th November 2011 21:27
If the wire you were using in the first few pictures has PVC insulation that would certainly reduce the Q of the resulting coil. PCV has very high losses at RF. I did think once of making a capacitor with pcv cling film for a special purpose (UWB transmitter). Anyway the best plastics to use at RF are polyethylene (HD,LD, or any type not containing carbon black), polypropylene or polystyrene (PS foam is even better). You cannot glue PE or PP but you can glue PS. While we are talking about long chain polyolefins you could immerse a variable capacitor in paraffin to improve its voltage rating and double its capacitance - useful for magnetic loop antennas. One problem that could potentially happen is that the oil could heat up enough to change to capacitance slightly and detune the antenna.
26th January 2011 14:41
John,
Thanks for that link, those coils are a work of art.
Regards,
Alan
16th January 2011 14:21
Have a look at http://www.crystalradio.net/crystalsets/hassell2/index.shtml
for an article that includes winding basket weave coils.
16th January 2011 14:16
It is important to note that plastic insulation on wires can have a very detrimental effect on the Q of a coil. The plastic insulation on household type wiring usually contain 'lossy' fillers such as carbon or metalic oxides. This also applies to plastic pipe used as a coil former.Place a sample in a microwave oven. If it gets at all warm, it is unsuitable to use in the construction of a high Q coil. Enamel covered wire is the best choice,or Litz wire if you can find some.
8th November 2010 03:55
Radiative losses can limit your Q as well as your measurement system. I have worked with very high Q systems and it is obvious that if they are not enclosed in a very conductive box the Q drops due to radiative losses. The Q of a system is equal to the energy stored in it divided by the energy loss per cycle. That may be multiplied by a constant determined by how a cycle is defined. If a cycle is defined by 2*PI radians there is 2*PI.
The energy is stored in the capacitance and inductance. It oscillates from one storage mechanism to the other.
10th September 2010 05:32
What is the material that you wrapped the second coil around? I can see one uses just string and another uses a drinking straw but the third is using a material that is not obvious. Does the material's parasitic capacitance and associated loss play into your Q measurement? Why not test that coil without it?
16th August 2010 15:17
ds,
Such coils are typically used in crystal radio receivers for the MW bands. High Q allows good system efficiency, which is important when only the energy being collected by your antenna system is available to drive the speaker allowing you to hear the signal.
Alternative technologies make this largely an exercise in geekiness. Some do it as a technical challenge, others as for historical recreation. I did it largely as a study of the physics of inductors.
Regards,
Alan
27th July 2010 05:44
I am curios about the "purpose" of the coil once constructed. I am not a scientist. thanks in advance
5th December 2008 11:55
Arv,
I've got some T200-0 cores (tan/natural phenolic material, mu ~ 1) I picked up from Kits and Parts but haven't found a use for yet. I'll have to give it a try, but yes that makes perfect sense from the geometry.
Winding toroids is a bit of a pain for a large number of turns. The commercial toroidal winders are very interesting machines, with an annular bobbin that carries the wire. The ring can be broken to insert the core then closed again, filled with wire and then reversed to spin the wire off onto the core. Check out the videos on YouTube of them in operation if you haven't seem them before. You could build something similar for manual use out of a piece of plastic channel section (maybe metal if it was flexible enough to be bent without fracturing).
Regards,
Alan
5th December 2008 10:26
Alan
Another "reduced capacitance" type inductor is one which is wound single layer on a fairly large diameter torus. Since the center circumference is smaller than the outer one, the windings are naturally spaced a bit apart on the outer part of each turn. Of course larger wire diameters work better than smaller ones.
Arv
_._
30th November 2012 00:07
vesa wrote...