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[OH4JFN]

I'm planning to stack 4-tribanders together. Now I'm asking information about impedance matching. I have planned to do it with ferrite toroids. Does anybody knows where can I find some information about impedance match when stacking tribanders?

73's OH4JFN

[W4AN]

I'm not sure where you find this information.  But I do know that Jay, WX0B, sells complete kits to do what you want.  You can see Jay's stuff at http://www.arraysolutions.com.

73

Bill

[N9CO]

I'm planning a modest 2 stack of tribanders, TH6 over KT34.
I know that one needs to keep the driven elements in phase.
This would be pretty easy if the stack was built from identical tribanders, but what do you do to insure proper phasing if one of the tribanders uses a dual driven element, like the KT34, KT34XA, TH7, etc., and the other tribander doesn't?

73,
Charlie  N9CO

[N6BZA]

It's hard to stack non-identical antennas.

The bottom line is that if you want to realize stacking gain (as opposed to simply being able to beam in two directions, or to pick the right antenna height for prevailing conditions) then you need to keep the antennas in phase on each of the three bands.  The key seems to be the feed system.  Assuming one driven element per antenna (not like the TET HB43SP for example, which is an HB9CV type antenna) you can deal with the geometry issues by aligning the driven elements one above the other (this may require some mechanical work, since the antenna's natural mounting locations may well not align the DE's).  You must actually align the DE's physically, you can't use delay lines unless you cut one line per band and use relay's to switch the right ones in.

I'm not familiar with the two antennas you are going to stack, but matching schemes frequently introduce phase changes that can vary depending on the band.  I strongly suggest that you:

1) Model the stack using a computerized modeling program.  This will let you study the phase issues without having to climb the tower.  You must model the actual feed system, which may or may not be possible.

2) Check the phase on the physical antennas.  I did this using a 500 Mhz dual input 'scope.  See my article at http://my.ispchannel.com/~djl .  Reality may not match the model...

Good luck!  Even if you don't get the phase right, you will see benefits just from having two antennas.

                   ***dan, N6BZA

[WX0B]

Thanks for the mention  Bill,

2,3,4,and 6 tri-banders can be stacked and have been stacked using the StackMatch line of products.

I am currently helping on a very large array of 6 Log-Periodics on a 200 foot tower as well.  

Jay, WX0B
www.arraysolutions.com is the site

[WX0B]

Stacking dissimilar antennas or tribanders, can be accomplished.

See my website for some customers that have done it succesfully.

In general,  I agree with Dan, N6BZA.  You must bring the driven elements into phase with each other.

Sometimes this can be done by  flipping the balun 180 degrees, most of the time it can be accomplished by adjusting one of the feedline lengths to accomplish the 0 phase relationship.  An O-scope is a good way to do this.

But it can also be done with an S -meter and some calculations of driven element compensation, and some trial and error.

It is not neccessary to have 3 different lengths of phase lines switched out from band to band.  Usually the driven element(s) are close enouph together that the distances are all the same or very close to being the same.  So a single delay line is all that is neccessary for all 3 bands.  What we are doing is compensating for a time mis-aliengnent with distance that is not dependant of the frequency.  The speed of light is the same on different bands.

I have found computer modelling to be not up to the task of actually giving us a good model of a matching device, unless its very simple like a split feed.  Aluminum tubes of different lengths and diameters, close together, with right angle bends just do not model well.

Now for a little different twist:

It may be actually to the benifit of the stacker to create a phase difference in a stack of antennas to broaden the forward projected lobe.  This will take advantage of all the angles of propogation vs making a small very narrow lobe.  The sacrifice is a little gain, but by filling in a null in the pattern you can see 10-20 db or more of "recovered gain" for this particular take off angle.  Its good to be able to switch the antennas around to change the angles, but its also may be of advantage for some skip conditions to actually "slur" the pattern into wider lobes by introducting phase delay into one of the beams.

I am gratefull for WA2VJN for pointing this out to me, and plan on putting it into my Stacking presentations as well as an application note on my web-site.  

I hope this helps someone to not throw out the baby with the bath water.  

Jay, WX0B