Elevated Radials for TriBand Beams

[aa5wg]

Hi to all:

A friend of mine is going to buy two TriBand beams and stack them.
His top soil is mostly sand, Michigan.

Will elevated radials under a triband beam help or is this a waist of time?

Chuck

[W4EWH]

A friend of mine is going to buy two TriBand beams and stack them.
His top soil is mostly sand, Michigan.

Will elevated radials under a triband beam help or is this a waste of time?

Tri-band beams are usually horizontally polarized, and having ground radials on the tower won't make enough difference to be worth the effort.

In any case, a tri-bander is a compromise design: the spacing and element lengths are not going to do well in "stacked" configuration. Your friend would do better to try a full-size beam for his favorite band.

Bill, W1AC

[K1JJ]

Chuck,

Bill is right on about the radials.  


A monobander for each band is a nice choice.  Optimized for F-B, gain and height above ground for each individual band is effective.

As an alternative, if he really wants to stack beams and make them multi-band, then a pair of  Tennadyne log periodics are a good choice.

Here's a pic of Chuck/ K1KW's quad-log installation.  Your friend could cut this in half and have a very FB multi-band system.

Also below is a pic of my own triple stacked homebrew 10M monobanders at 33' 66' 99' .

T

[KM1H]

Since a horizontal antenna obtains its ground gain from many wavelengths away the radials will do nothing.

Stacking tribanders has worked well for many, especially contesters. Its simple enough to model the stacking heights as simple monobanders and pick the compromise that gives the best pattern. Usually a half wave on 20M is used and Ive had excellent results using 40' with 40' boom 4el monobanders simply as that was the guy spacing and gave me minimal tower section twisting in high winds.
N6BV, who is the ARRL Antenna Book editor, had good results stacking 3 TH7's some years ago when he lived a few miles away and wrote about them in the NCJ and elsewhere. OTOH he could never beat my 4 stacks of 10-20M 4el monobanders

Carl

[aa5wg]

Bill, Tom, Carl and all:

Okay, the elevated radials are out. 

Are there any studies or test that show the comparisons, on paper,
of stacked monobanders compared to tribanders and log periodic antennas?

At present his tower has one log periodic multiband antenna.

Chuck

[KM1H]

If anybody would know its probably K1KW (WA1EKV), Chuck has tried just about everything and at one point had stacked very long HB LP's which created their own propagation. Unfortunately the big NE ice storm took them down in 2008 I think it was.

Id also look at the NCJ index for other possibilities.

Carl

[ke7trp]

I know guys that have stacked Moselys, TH7s, TH11s and stacked M2's. They sure seem to work well.  I think the guys are correct in that you will get higher gain stacking two mono banders.  

You can stack multiband beams, The key to this is to use the stack match.  This way you can steer the stack, and do BIP BOP.  Both in phase, Both out of phase.   These are designed to work with Multiband beams.

I have thought about stacking two moselys.  But its mainly just dreaming

http://www.arraysolutions.com/Products/stackmatch.htm

C

[KM1H]

Since ultimate gain is strictly a function of boom length the longer monobanders plus additional elements favored by most always win over a 14-24' tribander.

Trap and coil losses also come into play and their are continual arguments as to how much loss there is.

My own experience was a TH-6DX in the 60's against a 4el 10M monobander 90' away (a 40M Bobtail was between them) at the same height that was shorter but kicked ass and then here with a TH-6DXX against a slightly longer CC 4el 20M monobander on the same tower. There was no contest no matter which one was higher. Some felt the TH-6 was defective but in any case I sold the traps and used the aluminum to build more monobanders and the CC got stretched to 40' to match 4PV dimensions which I used on all bands.

[aa5wg]

Do you think two stacked average log periodics would outperform
two large stacked tribanders?  

Has anyone tried the WX0B StackMatch with stacked
tribanders or stacked log periodics?  If so how was
the performance?

Chuck

[aa5wg]

Tom:

Great looking 10 meter stacked antenna farm!

Chuck

[WA1GFZ]

as a LPDA driver (modified T12), I think once you go lpda you never go back

Chuck's stack is the balls.

[aa5wg]

Has anyone read the 1994 February QST article titled "Stacking Tribanders A Super Station Sorta" pages 38 - 44.

If so what do you think?

Chuck

[aa5wg]

Guys:

If there are two towers to work with (at present one Rohn 25) what would be a very good compromise design for 40- 10 meters?  Maybe only one antenna for 40 meters.

Chuck

[K1JJ]

Hi Chuck -

With two towers, I would use one for 40M and the other for 10-20M.

With Rohn 25, (torque limited)  I would put up a shorty 40, 2el Cushcraft 40 M Yagi at about 65'- 75' high.  

On the second tower, make it about 60' high and put a Tennadyne log at 60' and another one at 30'.  Use a side arm or ring rotator for the lower log.  Use equal feedlines and use a toroidal 0-180 phase switch system in the shack to cover high and low vertical angles.

For receiving, within reason, you will find that forward gain is not as important as front to back. And neither are as important as selecting the optimum incoming vertical angle.   For example, the difference between a 3el and 4el Yagi may be only 1db of forward gain. However, fading, as a result of having the incorrect vertical angle can vary as much as 20db, etc.   Having the optimum height for a single Yagi (or stacked Yagis) will suppress the higher angles as well as "fatten" the lowest optimum angles to keep fading to a minimum.

Generally we design the lowest lobe to match the desired band. For DX, (from the east coast to Europe) about 25-45 degrees is good for 75M.  40M is 25 degrees.  20M is 15 degrees  and 10M is 7 degrees take off angles.   Notice the angles roughly halve themselves as freq is doubled.   You can get these angles pretty close with modeling. Longer distances require lower angles and closer requires higher angles, of course. Optimum angles will also change with the solar cycle.

With a 40M Yagi at 70', you will get your optimum 25 degrees with little high angle.    The multi-band stack will be a compromise, optimized for 15M and the other bands will be off slightly, but not much.  10M will have some high angle but 20M will be very clean at 60' and 30' using small logs.  The bigger the booms, the wider the spacing required.

Your questions about traps can open a hornet's nest of debate, but generally, it is best to eliminate all traps, coils and others devices used to shorten and tune these low impedance Yagis. These can rob ~0.5 - 2 db from the overall forward gain depending on design and frequency. A 3el Yagi has only about 4.5db gain over a dipole, so there is not much to play with.  Remember that front to back is easy to get. Even a lossy loopstick has a good front to side. But getting forward gain over a dipole? Now THAT is difficult and separates the good antennas from the poor. Just cuz a Yagi turns and shows a big f-b and f-side means nothing about forward gain and losses. As Carl said, it requires two antennas that are A/B tested - at the same heights and spaced far enuff away from one another to prevent interaction. A reference dipole at the same height is a great antenna to determine forward gain and how well the Yagi is really working. I have been disappointed more than once after thinking a Yagi was tuned well and kicking ass when compared to a good dipole.

The most efficient system is a mono-band Yagi, followed by a log and then the various trap antennas. The interlaced, trapless Yagis are OK, but usually VERY complex and have wind/ice  loading and potential maintenance that scares me personally.

Simple is usually best and a monoband Yagi or log is hard to beat.

Good luck -

Tom, K1JJ


Below:   Yes, it's over the top, I know... :-)  Triple stacked, full-size 40M homebrew Yagis at 65', 125' and 190' fed in phase. This produces a single lobe on the horizon at about 11 degrees IIRC.  The angle is a little low for western Europe (UK) but when working Russia and Middle East areas, it is quite the antenna.  Built from scrap yard aluminum, cheap but strong.

[aa5wg]

Hi Tom and all:

Great information!  And, what a fantastic picture of the stacked 40 meter farm!!

I am going to study this material and get back to you and everyone.

By the way, do you know or anyone else know how much gain and take off angle
a two element and 4 element lazy-H hung vertically would have?  Or, should we
hang the lazy-h horizontally?

Please correct me if I am wrong.  For three band coverage the lazy-H would be cut for 10 meters
(at the double extended zepp length) to cover 10, 15 and 20 meters.  

My friends stacked antenna dream is in the middle of a dense forest.  The trees are 60 - 80 feet tall
and maybe a couple at 90 feet.  I was thinking of hanging the lazy-H and a dipole for reference.

Chuck

[K1JJ]

Chuck -

The double extended elements in the form of a 10M Lazy H is a great antenna. However, it will generally work better in the horizontal position IF you can get the proper elelment heights AND keep the elements reasonably straight. Inverted vee style Lazy H elements tend to degrade the gain and f-b from my modeling and actual experience in the field.

A vertical Lazy H would need an extensive ground screen system, just like any vertical system, but preferably even bigger to accomodate the far out ground reflections for the lower angles.  20-10M requirements are not as bad as 75M, of course.

The vertical H may be easier to support using trees vs: the horizontal, but every time I've tried vertical arrays like that I tore them down and went back to horizontal where there was no ground screen radial requirements. I must admit the ground conductivity here is poor. There was a time when I went thru 18,000 ft of #5 copper clad aluminum wire doing experiments. I tried everything I cud think of back in the mid 80's before I got any modeling software..

Check with TCI on the web. They make large shortwave broadcash arrays and always recommend an extensive ground screen with their vertical wire arrays of many kinds.

That said, even a simple mono-band 10M Lazy H with reflectors is a great antenna and not all that hard to support horizontally using trees.

One of the guys here could model it, but I would expect a lazy H with reflectors to have about 7-8 dbd gain or so. (over a dipole - 8 element array)    A bidirectional 4el w/o reflectors would be about 4-5dbd or so.   There is some wire loss in there on 10M, maybe a 1/2 db depending how sharply tuned the reflectors are resulting in a lower impedance.

The downside is it is not rotatable and the beamwidth is rather narrow. Probably about 35 degrees or so on 10M IIRC. So aim it well.  On 20M it would be about as wide as a dipole.

You COULD add reflectors for your favorite band (10M) for directional coverage and they wud be invisible on 15M and 20M giving a bi-directional pattern.


T

[WA1GFZ]

Tom,
I think my R25 is pretty maxed out with a single T12. Even with anti torque brackets every 17 feet. My modified one is much heavier with bigger elements.
My suggestion save your money and put up R45.

[KM1H]

Id suggest using TA (Terrain Analyzer) before settling on any particular antenna height if you have anything different than flat good conductivity ground.
It comes as part of the Antenna Manual software package.

BTW, Rohn 25G can take a lot of abuse when mounted on a pier pin, and using torque arms with 1/4" EHS instead of 3/16". The guy wires do most of the work when tensioned properly. Ive had a 100' loaded from the 25' level to the top of a 24' mast with stacked 4el yagis for 10-15M plus big  VHF/UHF arrays.

Carl

[aa5wg]

Tom, Carl and all:

Tom, again thank you for the great information.  And, Carl thank you for the tip on terrain
calculating.  

I was re-reading W8JI's site about the Lazy-H and he did not mention anything about radials with his vertical lazy-H.  How would one connect radials to a vertical orientated Lazy-H?

Would such an antenna have a lower take off angle that the tradition horizontal Lazy-H with the same gain?

I will ask some more questions regarding the Lazy-H with another post?

Chuck