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Summary: Phasing 2 tribanders - coax length

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Subject: Summary: Phasing 2 tribanders - coax length
From: (Lynn D. Osterbur)
Date: Mon, 14 Oct 1996 19:18:03 -0500 (CDT)

Here is the summary of comments regarding phasing 2 tribanders.  THanks to

all you have replied.  I will use a KT34XA at 103 FT and a Cushcraft A4 @

75 Ft. I did this once before with unequal (also unknown) feedlines.  It is

very convient when antennas are aimed in different directions. 73 to all

de Lynn

Lynn; If ur going to use all three bands, use 1/4w (246/f (MHz)X VF 

lines to each 3 bander.



I am thinking of phasing 2 tribanders.  Approximately 28 feet vertical

>seperation.   What would be the optimum spacing and length of the

>transimssion lines.

Before I can comment on this, you must first tell me what the height of the

lower tribander will be with reference to ground. If you are dealing with

low tower heights (<70 feet) you will be forced to move the spacing between

the two antennas tighter, since the ground reinforcement will cause a

resulting high angle addition with the summing of the lower tribander. In

theory, and in practice, the OPTIMUM stacking of .35 wavelength boom yagis,

is about 5/8 wave seperation. If you only have a short tower, this is not

possible. If you do have the tower resources, go with 5/8 wave spacing.

>I will use a remote coax switch to select : either or both antennnas.

>I am coming up with about 28 feet of 9913 (flexible).  How critical is

>this lenght other than the fact they must be equal?

Shown 32%, press <SPACE> for more, 'q' to quit, or 'h' for help>Comments 
welcome..   73  Lynn

As far as the phasing lines are concerned, you may go with either 1/4 wave

transformers, or is you please, go with 3/4 wave transformers. Cut these

lines as close to 1/4 or 3/4 as you can, as this will affect your SWR

directly. Nextly, and just as important, make sure that any 50 ohm lines

included in the phasing lines are the same length also. It does not matter

what the length is, as long as they are both the same. You can also put the

75 ohmn transformer wherever you like in the system, provided that the 50

coax lines are connected properly, and adjusted for the same length.

The spacing of the yagis is extremely important, as it will affect

impedance, F/B ratio, and  broadness of elevation angle gain maxima. This

is not easy to calculate, and is best simulated using a good yagi analying

program for your PC.

Again, all of the above specs change dramatically with yagi spacing with

regard to each other, and also with respect to ground. You also try to

increase yagi spacing, since if the spacing is too small, when you try the

lower yagi by itself, it will fall victim to the 'umbrella' effect of the

upper yagi.

It is important to note this fact when designing the stacked system, as the

Shown 67%, press <SPACE> for more, 'q' to quit, or 'h' for helpupper antenna is 
not really affected to a great degree by the presence of

the lower antenna, but the reciprocal does not hold hold true. The F/B and

gain, and elevation angle of gain maxima is affected dramatically in the

presence of the upper antenna. You can also adjust to any desired radiation

angle HIGHER than that which you can achieve with the upper antenna alone,

by altering the phasing between the yagis. For example, by shifting the

phasing of the yagis 180 degrees, you can lift the elevation angle gain

maxima by about 18 degrees, which can be useful in close in contesting


In stacking of yagis, I would stronly reccomend reading anything by the

late Jim Lawson W2PV. Among the best of his articles - is one that appeared

in Ham Radio Magazine in November of 1980- based on stacking and stacking

design. It is worth hunting down.

Hope I was of help.

73 de Shawn


dit dit

Shown 94%, press <SPACE> for more, 'q' to quit, or 'h' for help

Shawn Lightfoot




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Hi Lynn,

Have you thought about using LMR 400 which is made by Times Microwave.

If you look up Times Microwave on a search engine you may find some of

the answers you are searching for.

I think you may find that LMR 400 may be a better choice for your

climate than the 9913.

GL es 73

Dan Keefe  KS6Z

Lynn --

    Since you have to have phasing lines for each band, it is a complicated

and expensive job.  The best thing to do is get the Dunestar WX0B switch box

and make it a simple job.  Send Ron, AA7EA, a message at or

give him a call.  He's got the answers and the products.  Web page at

Shown 85%, press <SPACE> for more, 'q' to quit, or 'h' for help

     Don't use 9913 if the antennas will be rotated; the solid center

conductor will eventually break after flexing during rotation.

73,  Steve  K7LXC

Equal is critical. Length is always a compromise. -- Fred

Hello Lynn,

Interested in what you find out as will be putting up a tower with a

tribander and forty meter beam on top and later another tribander at about

the same spacing as yours.

Sorry don't have an answer.  


        Mike, K4GMH

From: (Tyler Stewart)

I assume you intend to use a stackmatch or some other matching xfmr system?

Cutting the feedlines to an odd quarterwavelength (electrically) can help

with even power division and matching to some extent, but that'll only

work on 1 band with tribanders.  Main thing is for the lines to be even 

lengths of the same material and may as well make them as short as possible.

73, Tyler KF3P



From: (Tony Brock-Fisher)


Any length can be used as long as they are electrically identical. Take a piece

of coax long enough to reach from on antenna to the other, with spare, and

cut it exactly in half - voila! phasing lines... Of coarse, you want to

use a transformer at the remote coax switch to correct the impedance.

There was a schematic in the K1VR/N6BV QST article back a few years ago,

but it contained errors. You can check the W2FMI book, or reply to me

for more details.

On the other hand, unless the antennas are both higher than 70 feet, I wouldn't

bother with this until the sunspots come back. It won't be worth the effort

until the elevation angles get higher...


From: (Jay Terleski)

Take a look at the Dunestar web page and save yourself a nightmare.    The Stackmatch is designed to precisely do what you

want and with equal legths of 50 ohm coax.  Seperate them 1/2 wave apart 

at the lowest freq. 


From: (Rod Fitz-Randolph)

Lynn, the length of each line from your relay/switch to

each of the tribanders is not critical and you are correct,

the lines must be of equal length IF you want the two beams

to be in phase with each other.  There was an excellent

article, not too long ago, in The National Contest Journal

(I think) about how one could phase shift the beams to give

a lower angle of radiation... but that is in an area of

which I know little.

I would strongly suggest you get a DX Engineering Phase Box

that will allow you to select either or both of the antennas

and will allow you to use 50 ohm coax in all cases.

Otherwise, you are going to run into difficulties with the

two leads going to the tribanders when you attempt to use

both at the same time.  You will reflect a 25 ohm to 50 ohm

mismatch at the junction where they come together and attach

to your main feedline.  With the DX Engineering Phase Box,

it is 50 ohms in and 50 ohms out in all cases.

73 es best DX.  Rod, W5HVV


                                  GL es DX   Lynn


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