Mathematically challenged

[Chuck Gehring]

I want to try and build an HF two Element Vertical Antenna for 20 meters.

While there are several java scripted web-sites that will calculate and provide the physical measurements for the Driven, Reflector elements and spacing.  

I would like to use my MJF-259 to complete the fine tuning during construction and given that the frequency of the Driven element will not be the resonant frequency of the reflector.  

What would a good equation be to determine the resonant frequency for the reflector based on the desired frequency for the Driven element?

Some references that I have found state the Reflector is approximately 4% longer than the Driven and the Director is 4% shorter, with element spacing 0.15 to 0.25 of the desired freq.  I would like something a little more specific.  Not that I can build it to spec or that the MFJ259 will be that accurate, I would still like to work with figures that provide something other than approximate.

73 K2CG
Chuck G.

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I am a little confused here as to what you want to build.  A two element beam or a two element vertical array.  Then you go on and site information about making a "beam."

These are two different animals.  

So, here are the calculations.....in feet

1/2 wave dipole - 468/F or 468/14.2 (20 meters) = 33.2 feet.  Now that is a half wave so to get a full wavelength just double the number of 66.4

According the all the books, the director should be 4%-5% longer.  So all you have to do is take 33.2 times 1.05 which comes out to 34.8

To figure the spacing...that the full wavelength number and take it time what you need....lets say .2  Then you get 13.28 feet.  Now there is a lot of wiggle room on the boom....you might want to model this before you actually build it, but that is a starting place.

So, now if you are looking on a vertical on 20 meters....well that is a different animal all together.  You could use a parasitic vertical but that would be hard to turn.  In fact, the two element vertical for 20 meters would be stationary or you would have to have a big wheel or something.  You could also use two quarter wave elements on 20 with some pretty good counterpoise wires under them and then space them a halfwave apart...33.2 feet.  Then you would feed them in the middle with a coax "T" connector.  That would give you a basic figure-8 pattern.  As you can see it would be stationary, unless you have some pretty good real estate....and some way of turning it.

So, I wonder if you could clarify what exactly you are looking for....

Lee - K0WA


In our day and age it seems that Common Sense is in short supply.  If you don't have any Common Sense - get some Common Sense and use it.  If you can't find any Common Sense, ask for help from somebody who has some Common Sense.  Is Common Sense divine?
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[N5GE]

On Fri, 16 Nov 2007 11:50:44 -0800, you wrote:

>I want to try and build an HF two Element Vertical Antenna for 20 meters.
>
>While there are several java scripted web-sites that will calculate and provide the physical measurements for the Driven, Reflector elements and spacing.  
>
>I would like to use my MJF-259 to complete the fine tuning during construction and given that the frequency of the Driven element will not be the resonant frequency of the reflector.  
>
>What would a good equation be to determine the resonant frequency for the reflector based on the desired frequency for the Driven element?
>
>Some references that I have found state the Reflector is approximately 4% longer than the Driven and the Director is 4% shorter, with element spacing 0.15 to 0.25 of the desired freq.  I would like something a little more specific.  Not that I can build it to spec or that the MFJ259 will be that accurate, I would still like to work with figures that provide something other than approximate.
>
>73 K2CG
>Chuck G.
>

[snip]

Back when I was a Novice I built a 15m 2 element Yagi using the information for
Yagi's in the ARRL antenna book.  I chose to build a driven/reflector style
beginning with a reflector length of (468/f in mc) X 1.05 and DE length of 468/f
in mc.  It worked very well.

 
Tom, N5GE

http://www.n5ge.com
http://www.eQSL.cc/Member.cfm?N5GE

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[Joe-aa4nn]

Here's something to think about and it is doable and a no-brainer.

Phase your two verticals.  Make each vertical a 1/4 wave and space
them 1/4 wave apart.  Tune each one independently for your favorite
frequency.  Get the ComtekSystems Phased vertical box with
associated feed lines and you are in business.
With the phased verticals you can selectively switch for end fire
in either direction in line with the verticals, plus you can switch
select to transmit broadside to the two elements.  Amazing results.
Excellent front-to-back as well.
de Joe, aa4nn
 
----- Original Message -----
From: <[hidden email]>
snip
>I want to try and build an HF two Element Vertical Antenna for 20 meters.

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[Dale Holloway-2]

Isn't it still a beam, whether vertical or horizontal, as long as it's got a
parasitic element? --Dale, K4EQ


> -----Original Message-----
> From: Lee Buller [mailto:[hidden email]]
> Sent: Friday, November 16, 2007 2:51 PM
> To: [hidden email]; Elecraft Reflector
> Subject: Re: [Elecraft] Mathematically challenged
>
>
> I am a little confused here as to what you want to build.  A two element
beam or a
> two element vertical array.  Then you go on and site information about
making a
> "beam."
>
> These are two different animals.
>
> Lee - K0WA

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[Chuck Gehring]

Joe,
Making and working with a Phased array is also on my to-do list but I plan on building the phase box.  For now I want to play with a vertical beam and using the planned operarting frequency times 1.05 gives me the resonant freq for the reflector provides me the information that I want to use when adjusting the reflector with my MFJ259.
My thanks to everyone that replied.  Being Mathematically Challenged (not really) I needed confirmation that I was on the correct path with my math :)

Chuck G.
---- Joe-aa4nn <[hidden email]> wrote:

> Here's something to think about and it is doable and a no-brainer.
>
> Phase your two verticals.  Make each vertical a 1/4 wave and space
> them 1/4 wave apart.  Tune each one independently for your favorite
> frequency.  Get the ComtekSystems Phased vertical box with
> associated feed lines and you are in business.
> With the phased verticals you can selectively switch for end fire
> in either direction in line with the verticals, plus you can switch
> select to transmit broadside to the two elements.  Amazing results.
> Excellent front-to-back as well.
> de Joe, aa4nn
>  
> ----- Original Message -----
> From: <[hidden email]>
> snip
> >I want to try and build an HF two Element Vertical Antenna for 20 meters.
>

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[Geoffrey Mackenzie-Kennedy]

Yes. The family of beam antennas also includes in addition to antennas using
parasitic elements such as the Yagi,  arrays of two or more driven phased
elements,  one or more radiating elements in front of  a plane reflector, a
termninated rhombic, a helix and many other types. . IIRC sometime in the
dim past many hams started to call yagis  'beams', which they are, but all
other types of antenna system which also exhibit unidirectional patterns and
are 'beams' by other names. I don't know why the Yagi, which is just a
member of  the 'beam' family of antennas, received this preferential
treatment.

73,
Geoff
GM4ESD

----- Original Message -----
Dale Holloway <[hidden email]> wrote:


> Isn't it still a beam, whether vertical or horizontal, as long as it's got
> a
> parasitic element? --Dale, K4EQ
>

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