[Boatanchors] Beam elements

[RAY FRIESS]

This is my theory from what I understand of antenna operation/theory...

 

An antenna that is resonant on 20 meters is resonant on 20 meters and it doesnt matter
what "components" it is made of?   In a tribander, the 20 meter resonant driven element is made up of the tubing with a combination of 15 and 20 meter traps in the circuit to physically shorten the length on 20 meters.   The 40 meter traps are added to make the beam driven element resonate on 40.  Electrically resonant, but physically shorter than a regular 40 meter dipole. 
 
A wire/tubing dipole is going to be just as resonant, only longer physically.  Antennas have many different designs to make them fit into different spaces, but electrically, they all resonate on a particular band ..  they're just differing lengths, depending on whether you use a certain type of trap or loading mechanism.
 
Therefore, a tribander driven element with the traps in the element is going to be just as resonant on 20 meters as a dipole cut for 20 meters ... whether the dipole is cut from wire or from tubing..  give or take a bit for the diameter of the tubing and other factors that affect the length of a wire or tubing element.
 
So .. If the tribander driven element is equal to the wire or tubing dipole, then the traps would have the same effect on the tribander driven element and the wire/tubing 20 meter dipole.    In other words, if the tribander driven element is "A" and the wire/tubing dipole is "B" and A equals B, then the traps will have the same effect on B as they would on A.
 
Ray


 
> From: k2gkk at hotmail.com
> To: rayfrijr at msn.com; boatanchors at mailman.qth.net; flboatanchors at yahoogroups.com; glowbugs at piobaire.mines.uidaho.edu
> Subject: RE: [Boatanchors] Beam elements
> Date: Tue, 12 May 2009 20:33:55 -0500
> 
> 
> Hy-Gain used to market a rotatable dipole for
> 40/30 meters. It was basically full half
> wave for 30 meters and used linear loading
> to "lengthen" it for 40 meters. I had one
> of these set on 30 meters 10 feet above my
> Mosley PRO-67 beam. It worked fine, but the
> whole deal, tower and all, went away along
> with the house when Mister Twister came
> calling on 3 May 99!
> 
> 73 - Mac, K2GKK/5
> Oklahoma City, OK
> 
> ________________________________
> > From: rayfrijr at msn.com
> > To: k2gkk at hotmail.com; boatanchors at mailman.qth.net; flboatanchors at yahoogroups.com; glowbugs at piobaire.mines.uidaho.edu
> > Subject: RE: [Boatanchors] Beam elements
> > Date: Tue, 12 May 2009 19:06:33 -0600
> >
> > Thanks.
> >
> > I am toying with a idea. I have the traps that were made to add 40 meters to the driven element of my triband beam.
> >
> > I never put the on because I thought it would be too unwieldly for my location, and I didnt want to add the extra guying that is usually added to the driven element.
> >
> > I was looking at them the other day and thought using them to construct a rotatable dipole for 40 meters might be worth experimenting with. That's why I wondered what the electrical wavelength of a triband beam element usually is.
> >
> > I was thinking that since the next band down from 20 meters, as far as the driven element of a tribander is concerned, is 15 meters, that if I made a 20 meter half wave antenna out of tubing or wire, and used these traps that maybe I could get the homebrew antenna to resonate on 40 meters, as it would do if I put them on the driven element of the tribander like they would do if I added them to the beam.
> >
> > If so, I could manage such a rotatable dipole, where it would be too unwieldly to add them to my tribander.
> >
> > What do you antenna experts here think?
> >
> > Ray WA7ITZ