Theremin Antennas

Posted: 3/28/2007 3:31:19 PM

From: Jax, FL

Joined: 2/14/2005

Parsa, tubing is better than rods because it is less likely to vibrate or wiggle back and forth.

Posted: 3/28/2007 6:39:15 PM

From: Escondido, CA

Joined: 3/25/2007

Really, I would have thought just the opposite. Why would thin-walled tubing wobble or vibrate less than a solid rod?
Posted: 3/28/2007 7:56:25 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

I learned this at school. Long time ago now, so I'm a bit rusty. It's this whole structural mechanics thing, with compression and tension stresses. As I recall explaining it took diagrams and looking at Perspex cylinders with polarising lenses but it pretty much amounts to - it's the outside of a rod that gets stretched or compressed most, and as long as that's retaining its integrity the insides are basically dead weight - once the outside stretches or compresses the rest just follows suit - all the insides do is add mass and hence momentum which means the free end of rod is more inclined to keep moving once you start it moving by waving it around or twanging it.
Posted: 3/28/2007 9:05:29 PM

From: Kansas City, Mo.

Joined: 8/23/2005

... besides, solid rods are heavy compared to tubes. Rods will give your instrument a higher center-of-gravity which would, all other factors being equal, tend to wobble more than an instrument with a lower cg.
Posted: 3/29/2007 12:33:05 PM

From: Escondido, CA

Joined: 3/25/2007

OK, both these make sense.... Although I've read through a whole lot of old threads here, I am still going to ask.
What is a good easily available tube material for the pitch rod? Is brass a favorite? Or is it best just to get some old antenna off a set of unused rabbit ears?

I may also opt for the Lev antenna. It might look cool to have a spring in a transparent tube so you could see it. That would look pretty "spacey." I wonder how different tube materials affect the dielectric of the capacitor. (I've thought of that in regards to a plate too. It would be interesting to use some big spongey materials between your hand and the plate to see what they do. Just for physics fun of course.)
Posted: 3/30/2007 3:39:20 PM

From: Gambier, OH

Joined: 3/30/2007

Hi, I'm sorry if this is a weird question. This is my first post here, and I've never actually built a theremin before.

I was just wondering, is there any way I could successfully create antennae for my theremin between 8' and 10' tall? I talked to Art Harrison about it a while back, but I didn't ever really ask what I should make them out of. Does anyone have any ideas?
Posted: 3/30/2007 5:30:51 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Welcome to Theremin World.

Yes it is possible. I think there's a woman at MIT you want to talk to. See Brian R's recent posting (#3 on the previous page of this thread.)

Posted: 3/31/2007 11:38:25 AM
Charlie D

From: England

Joined: 2/28/2005

I'd say metal piping's probably your best bet. Go somewhere that does plumbing supplies, and just take a look around. With regards hollow/solid - the RCA antennas are far heavier than the E'Pro's. I think the choice would depend both on the circuitry (and E'standard wouldnt cope with solid antennas), and, as Kevin said, on whether solid antennas would cause the thing to topple over. Basically, if you're making it yourself, either will work. Price and appearance should be a bigger concern.

P.S Antennae are things insects have. Antennas are metal poles.
Posted: 3/31/2007 3:09:05 PM

From: Escondido, CA

Joined: 3/25/2007

Hehe, I think antennae is the plural form in Latin, but that the modernized form is antennas. The same is happening with other Latin words like formulae, formulas; fora, forums; memoranda, memorandums; cacti; cactuses; octopi, octopuses; dogmata, dogmas; etc. (The first listed are the correct Latin plurals.)
In truth, the things on the theremin aren't antennas primarily anyway, they are capacitor plates. However, they can generate and pick up EM waves which isn't often a wanted property.
Posted: 3/31/2007 3:21:49 PM

From: Escondido, CA

Joined: 3/25/2007

OK, so I should go down to a plumbing supply place and look at the pipes. Sounds good. Is the choice more a matter of esthetics than function?
I have some questions...
1. Do you cap off the tube with something or leave it open?
2. Do you prefer plated tubes or like the clean metal (brass, aluminum).
3. What is the best way to attach the tube? I noted reference to compression fittings, but I've never done any plumbing so don't really know about this stuff. I'd love to see closeups of how people mounted metal rods.
4. If the chassis is metal, the rods must be isolated. I'm assuming I can mount the rod on an insulator and run an insulated wire into the chassis, right? Or I can run the rods through rubber grommets or something.
5. If anyone has built the Lev Antenna, I would be interested in seeing a close up of how you mounted it. Christopher sent me some photos of his, but they are a bit small.

I've seen some clear PVC tubing and fittings. That might be a way to go as it would be cool to be able to see the spring.


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