Glue Stick Variable Cap

[KJ4IVD]

The March 1 edition of Radio World Newspaper (trade paper for broadcasters) features a great 15-minute project: turning an empty glue stick into a variable capacitor, with a whopping range of 10-12 pf.

http://www.nxtbook.com/nxtbooks/newb.../index.php#/18

Maybe not a terribly useful item, but for coming up with it, Frank Hertel (the engineer submitting the tip to RW) is "MacGyver" of the Week in my book.

[K8ERV]

Wonder what it's temco is?

TOM K8ERV Montrose Colo

[K9STH]

VJD:

At VHF and UHF, the capacitance variation range is more than enough to tune the resonant frequency through a fairly large range.

This capacitor might be a good candidate for a VHF or UHF receiver local oscillator or for a VFO that is multiplied several times to get to the desired frequency.

Glen, K9STH

[VK2HHS]

So simple it's genius.

I'm sure the basic idea can be manipulated to drive a slug in and out of a close spaced winding on the outside of the tube to make an excellent component to be used in controlling a permeability tuned oscillator

de VK2HHS

[WA9SVD]

So simple it's genius.

I'm sure the basic idea can be manipulated to drive a slug in and out of a close spaced winding on the outside of the tube to make an excellent component to be used in controlling a permeability tuned oscillator

de VK2HHS

But as Tom implied above, if the temperature coefficient isn't stable or predictable (and I'd wager different brands and even batches of glue have different characteristics) it's purely an experimental design and would need some careful and rigorous testing before considering such a "device" in any frequency critical or frequency stable use.

[KL7AJ]

I maked a PTO with a mechanical pencil and a ferrite bead once. Worked really good too!
Eric

[KA9JLM]

You can also twist two wires together and get the same result.

It was called a Gimmick (in old school days), and was used for low PF cap needs.

Stability depends on the type of wire used, and the Cap value is set by the number of twists and length of the wire.


That is a interesting article. Thanks for sharing.

[4L4AGU]

Absolutely not new. We have done this with empty lipstick, at least 20 years ago.