I want to know everything about the antenna

Posted: 11/6/2007 4:39:45 PM
Diuretik

From: France

Joined: 11/6/2007

Hi everybody,

I'm making an one-antenna Theremin, cause i'm a beginner in this field... I have some pretty good results, but i would like to increase the sensitivity of my Theremin through a good choice of antenna.
I have a lot of questions, that were probably ever answered somewhere, but i didn't find by myself...
What is the best material for the antenna ?
Is it better a sheet-steel antenna, or a cylinder one ?
Do the length and the diameter are important ?

Thanks for your help,
Guy (sorry for my english... but i do not practice it very often...)
Posted: 11/8/2007 6:09:38 PM
omhoge

From: New York, NY

Joined: 2/13/2005

Welcome to ThereminWorld.
I wish I could help.

Do any of the theremin constructors out there have some suggestions for antenna materials?

Good Luck!
Posted: 11/8/2007 10:01:02 PM
therem13

Joined: 9/25/2007

I haven't made a theremin yet, but the article located at http://emusician.com/diy/em_theremin/ describes how to make antennas for Robert Moog's EM Theremin.
Posted: 11/9/2007 5:02:40 PM
jluciani

From: Massachusetts

Joined: 8/18/2007

I used an antenna salvaged off of a broken
radio.

(* jcl *)
Posted: 1/10/2008 8:08:10 PM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

I have used three different antennae with my theremin. one was a telescoping radio antenna. It didn't seem to work very well at all, but I didn't know much at that time so... The other two were solid brass and brass tube. They both work equally well. Both were 7/16" diameter. I had to adjust the capacitance of my variable pitch ocsillator to get optimum performance with each. That is probably the key with any antenna you choose. Good luck.
ba
Posted: 1/11/2008 12:27:07 AM
Alan_in_CA

From: Fresno, California USA

Joined: 3/26/2006

Brass tubing is usually too hard to bend without special equipment. Some special types of copper tubing may be hard enough but some are too soft. Aluminum is a good compromise for flexibility and stiffness.

http://www.abarbour.net/tmax.html
Posted: 1/11/2008 10:38:19 PM
organ man

From: Kalamazoo, MI

Joined: 3/20/2006

this is true for the loop antenna. I did bend one out of solid brass and it was hard as h---. However, there is nothing that says it has to be 7/16" diameter. If you look at a picture of Leon Theremin's first theremin, he used what looks to be 1/4" diameter brass. I'd use whatever you can find at the hardware store.
Posted: 1/12/2008 3:55:37 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

"Normal" antennae are designed to have best free-field adaption, that means that most of the electrical energy has to be diffused to air at a long distance. So their most important design factors are wavelength and polarisation.

These both factors are not really important for a theremin, since an antenna should act here as one part of a capacitor, your hand beeing the other one.

So, to form a mostly ideal capacitor with you, the antenna should have an important surface area, and this on its whole lenght, what may explain that telescopic antennae don't give satisfying results.

The second factor is that the electrical resistance of the antenna may become important, since this adds an unwnated attenuation factor. That means that copper should work better than aluminium.

The third and last thing is the linearity of the pitch antenna which seems to increase with its inductive reactance. That's why there are several coils in series with the antenna inside the Moog Etherwave... Finally an antenna in form of a tube has a better inductance and will give better results than a massive one.

So take a copper tube or still better a silver tube :-)))) with around 1 to 1.5cm in diameter and an length of around 50cm. You may try to optimize it by cutting pieces of 0.5cm down to 40cm and you should find an optimum.

Don't forget to retune your theremin after each modification since inductance of the antenna will slightly decrease with each piece cutted of.

If you have problems in understanding all this in English, just send me your questions in French at frenkel.thierry(at)orange.fr

I will answer you in French and in case the questions and answers are of common interest, I will post a summary in English here.
Posted: 1/14/2008 1:04:10 AM
Alan_in_CA

From: Fresno, California USA

Joined: 3/26/2006

Ah, yes, silver--but pure silver, not mere sterling silver. The difference in appearance is obvious. Really beautiful.
Posted: 1/14/2008 1:55:36 AM
Thierry

From: Colmar, France

Joined: 12/31/2007

:-))))

It seems to be amusing, but it is a fact that in many RF designs silver plated copper wire is used, in order to improve surface conductance.

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