antenna construction

Posted: 2/17/2011 6:26:58 PM
mraroid

From: Portland Oregon

Joined: 2/15/2011

Hi

What were the original 1920s antennas made of? I have read about using brass tubing and having it nickel plated. Is this what is usually done? Is the diameter of the tubing "off the shelf", or do I have to special order a specific odd ball size?

Thanks

jack

Posted: 2/17/2011 10:01:24 PM
Chobbs

From: Brooklyn,NY

Joined: 12/1/2009

any "off-the-shelf" tube from an art or hobby store is going to be thin walled and will bend miserably- kink and collapse. You want the thicker walled stuff that can be ordered from McMaster-carr. 0.06??something at least. Maybe temper and/or pack with sand.

Use any diameter you want. Nickel plating just stays shiny. Brass tarnishes.
Posted: 2/17/2011 10:40:43 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Yes, they are nickel-plated brass. Our best guess is that it is 7/16" O.D. x 0.065" wall tubing. My research concluded that C260 alloy (cartridge brass) would be best for bending the loop antenna.

Obviously, no one is crazy enough to cut their antennas, so I had to estimate the thickness of the tubing by the total weight of a complete antenna.

RCA used what they thought was best or just easiest to get at the time. They gave no thought as to whether it would be convenient for YOU ninty years down the road. You always have the liberty to make your own modifications, but if it doesn't work out, you have only yourself to blame.

You will find drawings at the bottom of this page (http://www.thereminworld.com/article.asp?id=27) that should clear things up for you.

I have parts available for a set if anyone is interested. Because of the material and machining costs, they won't be cheap. You'd have to cut, bend, and solder the tubing yourself. You'd also have to have them plated, which isn't cheap either.
Posted: 2/19/2011 5:43:22 PM
mraroid

From: Portland Oregon

Joined: 2/15/2011

Thanks for the good info. I keep finding new place on this web site to explore. Time to keep reading.

jack
Posted: 5/10/2012 5:16:58 PM
gnsmith116

From: Northern Virginia, USA

Joined: 5/10/2012

any "off-the-shelf" tube from an art or hobby store is going to be thin walled and will bend miserably- kink and collapse. You want the thicker walled stuff that can be ordered from McMaster-carr. 0.06??something at least. Maybe temper and/or pack with sand.

Use any diameter you want. Nickel plating just stays shiny. Brass tarnishes.

 

Chobbs,

Thanks for the pointer on using thicker walled tubing.  I've been searching around expecting to find some mention of filling the tubing with resin to stiffen it like Robert Moog suggested in the EM Theremin article but have not found anything.  Has that method been found to be unsatisfactory or in some way inferior to sand or using thicker walled tubing from the perspective of either strength, weight, or a negative effect on performance?  I just built up a Theremax (no box yet) and of course the first mod I want to make is to improve the antennas.  I figured to start with I would just use the 3/8" chrome plated plumbing supply tubing filled with resin to stiffen it.  That seems easy enough.  I have another question that someone might be able to answer.  Does it mater from a performance perspective if the top of the pitch antenna is closed (has a cap) or is that mostly an aesthetic thing?

Thanks in advance,

Greg

 

Posted: 5/11/2012 12:02:27 AM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

Greg,

I have not tried this method but on the Discovery Channel they showed how trombone makers used soapy water filling the tube then freezing it. Then they bend the curves in a jig. It worked perfect for them.

A closed top makes no difference once tuned.

Posted: 5/11/2012 12:55:00 AM
gnsmith116

From: Northern Virginia, USA

Joined: 5/10/2012

Greg,

I have not tried this method but on the Discovery Channel they showed how trombone makers used soapy water filling the tube then freezing it. It worked perfect for them. A closed top makes no difference once tuned.

RS,

Thanks for the reply.  The idea of the resin is after the tubing is bent or straight (whatever shape you want) you fill it with the epoxy resin and that makes the tubing stiff so it won't bend anymore when it gets hit even if it is thin walled.  When Chobbs said "maybe temper or pack with sand" I took it that he meant that those were also steps to keep it stiff after bending - I guess it was the "temper" that got me thinking that way.  So with the trombone, they use the soapy water to freeze into kind of a slush so the tubing doesn't collapse when it is bent?

 

Posted: 5/11/2012 3:26:33 AM
SewerPipe

From: Flying with the Phoenix

Joined: 3/9/2011

Greg,

When I built my PVC Sewer Pipe Theremax Theremin, I used 3/8"od. (Thin walled) nickel plated water line used for sinks. I made a simple wooden bend fixture for the vol. loop. I will be happy to e-mail the prints and a picture of the fixture if you want to go that route. I never filled them with anything and have had no problems  -- yet. I don’t "gig" with it so no accidental mishaps yet.

In His Service --- Dana 

 

Posted: 5/15/2012 9:27:23 PM
gnsmith116

From: Northern Virginia, USA

Joined: 5/10/2012

Greg,

When I built my PVC Sewer Pipe Theremax Theremin, I used 3/8"od. (Thin walled) nickel plated water line used for sinks. I made a simple wooden bend fixture for the vol. loop. I will be happy to e-mail the prints and a picture of the fixture if you want to go that route. I never filled them with anything and have had no problems  -- yet. I don’t "gig" with it so no accidental mishaps yet.

In His Service --- Dana 

Dana,

Sorry for the delayed reply.  Any information would be helpful.  I bought a "spring" tubing bender set but I think it would be really hard to use that and get a constant radius by hand.  The other idea I had was to turn a pair of "pulleys" made out of hard wood that would match the OD tubing diameter and mount them on an arm to pull the tubing into a circular shape.  You may have done something similar.  It there a way to send a private message on this forum?

Thanks,

 

Greg 

Posted: 5/15/2012 11:03:56 PM
SewerPipe

From: Flying with the Phoenix

Joined: 3/9/2011

Greg: My e-mail address is --- dda1800@comcast.net --- Please send me your address and I will E-mail those prints & pictures.

In the mean time go to here --- http://www.thereminworld.com/Article/14126/sewer-pipe-theremin --- to see pictures and article about my Sewer Pipe Theremin.

IHS --- Dana

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