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Old 20-Apr-2011, 7:58 PM   #1
newbobbyc44
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Smile Request for help with YAGI Calculator

Hi!
I downloaded the software for "Yagi Calculator", an item I have searched for on the Internet for some time now.....SO I am grateful for THAT!

QUESTION:
I have a manufactured 5 element YAGI cut for Channel 13. I want to extend the boom and add FIVE more directors to increase the gain, directionality and front-to-back ratio.
Can someone help me to get the numbers right before I start cutting and screwing the aluminum tubing I will be using? I will use materials similar to the original antenna (salvaged from an unused Channel 5 antenna)
Will all of this WORK for me and will the effort increase the GAIN much for me?

Would I be better to duplicate the 5-element YAGI and use stacking bars? What length would the stacking bars be? How do I calculate that? Is it 1/2 wavelength between the antennas, and reverse phase on one or something?

"See how CONFUSED I am???"
Sincerely,
Bob (NEW member)
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Old 20-Apr-2011, 9:04 PM   #2
GroundUrMast
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I would be reluctant to destroy a good factory built antenna. You can build a few inexpensive test / trial antennas using wood or plastic boom and wire elements. That would leave you a working antenna as a reference to compare performance against. You could then answer the question, "Will all of this WORK for me and will the effort increase the GAIN much for me?" for yourself. In theory, adding five more directors could yield 3 dB of forward gain... if you get it right.

450 ohm ladder line is a great stacking harness material, if you can find some. Open wire twin lead is easy to build, and Wikipedia has the formulas needed to calculate characteristic impedance.

Wavelength = Speed of light / Frequency

Channel 13's band center is 213 MHz, therefor 299792458 M/s divided by 213 MHz is about 1.4 Meters. Half of that is about 0.7 Meters.
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Last edited by GroundUrMast; 21-Apr-2011 at 4:54 AM.
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Old 20-Apr-2011, 9:10 PM   #3
GroundUrMast
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Quote:
Would I be better to duplicate the 5-element YAGI and use stacking bars?
That depends on what you are trying to accomplish. If you simply need more forward gain, stacking may not be the best choice. Stacking can produce more gain, but it can also be useful when you need to produce a tighter directional pattern. For example, you may need to reject co-channel or adjacent channel interference.

Stacking is almost always done with identical antennas, and offers an increase in forward gain of 3 dB minus the losses due to combining. Combining losses can easily exceed 3 dB depending on the method used.
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Last edited by GroundUrMast; 20-Apr-2011 at 9:19 PM.
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Old 20-Apr-2011, 10:21 PM   #4
newbobbyc44
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Thanks for your HELPFUL replies! (Rapidfire too!)

hi!
WOW!
You must visit here OFTEN to reply so quckly!
THANK YOU very much!

YEARS ago (about 1965?) at my parents' home I stacked FOUR 10-element wide-spaced YAGI's for channel 7! They worked great! I was pulling in COLOUR from WWNY-TV Watertown, NY from Ottawa, Ontario Canada about 120 miles away!

I wish I knew NOW what I knew today! I have a very nice photo of that array including tower and two FINCO FM-5 10 element YAGIs stacked on a rotor to scan the "heavens" for FM stations in Ontario, Quebec and NY State!!!

It is amazing to me that when only 21 years old I KNEW the spacing and got the phasing right for those Channel 7's!

THOSE were the days!

My TODAY project is so "minor" by comparison and I'm not sure of what to do!

My understanding was that as you increase the number of directors, you "squeeze" the front lobe making distance LONGER and the antenna aiming is more critical due to the narrow lobe!

Sound right?

Sincerely,
Bob
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Old 20-Apr-2011, 10:46 PM   #5
GroundUrMast
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Quote:
My understanding was that as you increase the number of directors, you "squeeze" the front lobe making distance LONGER and the antenna aiming is more critical due to the narrow lobe!
True.

Have you seen this info yet? http://forum.tvfool.com/showthread.php?t=1024
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Old 20-Apr-2011, 11:02 PM   #6
newbobbyc44
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Red face Yes! I DID read that post.....NEW request????

Hi!
I even printed out the 5 pages of the last item offered...."Stagger Stacking" by Bill Thompson!

NEW Request:
I have lots of old antennas so lots of salvage "raw" material to construct a NEWLY fabricated (by "me") 10 element Channel 13 YAGI.

IF I give you the diameters of the boom and elements, would you have the time and patience to run the "Calculator" and tell me the length and spacing of all the elements?

I wish I could find an old antenna somewhere and just COPY it!!!

Is there SOMEWHERE on the Internet that would give me these necessary measurements already DONE?

Sincerely,
Bob
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Old 21-Apr-2011, 12:14 AM   #7
GroundUrMast
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Here are two options, one uses insulation between the boom and elements, the other does not.

I presumed 1" square boom and 3/8" diameter element stock.
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