Hi-Q-coils

Quick suggestion. Get some representative samples of that magnetic liquid in the tube, and repeat the Fr+Q measurements for various additional loadings. This will give the other contributors on that thread some harder numbers to work with.

--
Tony Williams.

Eh? Toilet paper comes on rolls that are around 4cm diameter (1.5 or

1.75" looks like). Maybe the core from a small roll of thermal fax paper or printing calculator tape would be closer.

Best regards, Spehro Pefhany

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A used toilet paper roll is an excellent choice, as long as the paper is kept dry, and stability is not an issue. My first crystal-radio was based on one! So don't throw them away! They can be reused. :-)

>

--
Sven Wilhelmsson
http://home.swipnet.se/swi

I like to use TP tubes by slitting lengthwise, applying glue and rolling down the diameter until there's a bit over two full turns of paper overlapping. It gets to about 1" o.d.. Far stiffer than a single layer.

Tim

-- Deep Fryer: a very philosophical monk. Website:

was that a used toilet paper roll? :))

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

I remember to have seen coils in old tube radios that are rather spacy, where each layer was at an angle to the layer below. This reduced the inter- winding capacitances.

Rene

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It was called "wave winding".

Leon

One could get higher Q by using a cylindrical "shield" and changing the coil geometry to "fit"; an alternate view of that is a resonant cavity withslow wave structure; one name used is helical resonator.

I think there was another name, "pi wound"..

But the coil from a helical resonator, in free air without the shield, will yield a higher Q. The shield reduces the inductance but not the loss. In general, shielding a solenoid coil reduces its Q, and the helical resonator is no exception. (Helical resonators DO have advantages; that's just not one of them.)

Cheers, Tom

Your question leads to many others...

--Would a different geometry such as toroid work better?

--What exactly does "about this size" mean? That is, do you include only the coil, or the volume out to where the magnetic field is below some value, for a given tank stored energy?

--A related question might be, what's the best coil Q for a given shield enclosed volume?

--What is the point of diminished returns such that adding more layers is not worth the effort?

--How much difference is there between winding several layers insulated from one another, and using an edge-wound tape wire (rectangular- cross-section wire, much taller than it is wide)?

--How accurately can you predict the Q improvement by simply taking into account the coupling among the layers, and ignoring proximity effects from layer to layer, and how does that change with frequency?

--Is there any advantage to using (slightly) different numbers of turns per layer?

---and many more

Many thanks to Sven for this thought-provoking posting, and the work he put into the multi-layer coil and its measurement.

Cheers, Tom

Honeycomb coil, in german language Wabenspule

Jorgen

Q is not very critical to volume, but with enough space and money, there is probably no limit.

This is a critical point, I would think. Something should be equal for all layers, if not there will be 'short-circuit turns'. But is it number of turns, inductance per layer, or something else? I think there should be fewer turns in the upper layers, but I don't know the formula.

Yes, good questions above. I wish I knew the answers!

I have been trying to write a computer program to calculate coils from first principles, like the law of Biot-Savart, but soon understood that intelligent approximations are needed. So I need to better understand these things to go on with this work. Practical experiments could be a way, like discussions in this newsgroup. I don't have any books that penetrates this subject in depth.

--
Sven Wilhelmsson
http://home.swipnet.se/swi

Actually, believe it or not, that's "pie", because the little stacks of windings look like pies. :-)

Cheers! Rich

LOL :)

Try Low Frequency Electromagnetic Design, M.P. Perry, Marcel Dekker

Cheers Terry

These guys are into High-Q:

click on the advanced forum at the bottom of the page and when that page opens,in the drop down box in the top right of the page, click on "show topics for the last year".

You may be right, but the spelling i have seen used in many places was "pi".