[CQ-Contest] Two Towers, Two Tribanders - Coax Length for Stack Match?

[Jukka Klemola]

Hi all,
I cannot verify this theory in practice.

I have, on 20, 15 and 10 stacked yagis on two towers.
The towers are broadside to U.S East Coast and are in-line to JA.

If this pattern nulling theory would function in real life, I would
experience serious signa degradation when receiving stations in Florida and
I would turn my other tower to cover British Columbia or even further to
Alaska or Hawaii.

I am sorry to inform you that if I have my western tower pointing to 295,
which is a little left from the exact broadside direction, and I turn the
eastern tower to 340 degrees, while listening to VFO A on my left ear, to a
typical Maryland or any MidWest station, I hear no real QSB in the signal
when turning the eastern stack.
The only effect is, if I have a WL7 on the right ear, on the VFO B, the WL7
becomes audible.


The cause?
The cause at my location is the towers are 2 waves apart from each other on
20m.
There are all sorts of real-life phenomena coming into play.
The terrain is not exactly flat.
The antennas are not at equal heights.
The stack distances are not equal.
The elements droop a little .. and so on.

On 20, I have not found any measurable dipping or lack of signal when
pointing the two stacks to North America and rotating the other stack.

I have verified, however, the additional gain of running the stacks
broadside in parallel as compared to only single stack.
And, I have verified the case where other stack is turned away from North
America that the signal drops a little when I switch between combinations
of stacks .. beaming to, away, or both towers to North America.


About simulations:
any simulator I have seen support only the theoretical flat land cases.
The simulators show different results than real life produces.

What has been amazing in my experimentation, is the 20m stacks provide in
pattern cleanliness when pointing them in-line to Japan, Korea and Eastern
China direction.
Maybe also a little signal benefit, I have not really been able to verify
that, but receiving is better when the two stacks are together.


I have not done an extensive analysis on 15 or 10.
I know there have been some isolated cases a signal seems to drop much more
than 3dB when I switch into using both towers instead of only one tower.

In case anyone is interested in experimenting this in practice, please
contact me directly.



For anyone wanting to build these dual or triple .. or quadruple tower
systems ..
The eternal DX rule is for all of us. WFWL.
That is: work first worry later.

Keep on experimenting.


73,
Jukka OH6LI



2015-07-12 20:27 GMT+03:00 David Pruett <k8cc at comcast.net>:

> Rich,
>
> As I am sure you are aware, if the two antennas/arrays are in phase the
> field strengths add and if out of phase subtract.  Feed line length is only
> half of the question in regards to phase.  The distance between the towers,
> the direction of interest and relative positions of the towers in azimuth
> have just as much effect.
>
> If the antennas have good directivity and are pointed in different
> directions where the patterns don't overlap, then none of this really
> matters.
>
> I do a lot of multi-direction spraying at K8CC, but how I do it differs.
> I have a 2-stack on 20M plus a fixed SE yagi on another tower, a 3-stack on
> 15M plus a fixed SE yagi, but on 10M I just have  3-stack.  In a DX contest
> where I might try to spray towards different continents and I'm concerned
> about phase I just use the stack aimed in different directions.  But in SS
> where I like to spray everywhere I'll aim the stacks W/NW and SW and on
> 20M/15M I'll rig up an uneven power splitter with some coax and add the
> fixed SE into the system. (I use an uneven split to ensure most of the
> power goes to the stack, which is aimed in the primary direction of
> interest.). On 10M where I don't have a fixed SE yagi, I just spray the
> 3-stack NW/SW/SE.  It all works very well.
>
> 73, Dave/K8CC
>
> Sent from my iPhone
>
> > On Jul 12, 2015, at 8:14 AM, Richard Thorne <rthorne at rthorne.net> wrote:
> >
> > I'm in the process of putting up a second tower which will have stacked
> tribanders.  These 3 tribanders will be fed via a Stack Match with equal
> lengths of coax.
> >
> > My current tower also has a tribander.
> >
> > I plan on installing a stackmatch II switch between the two towers for
> quick direction changing or spraying my signal in 2 directions.
> >
> > Is it worth the trouble to use equal length feed lines?  If I use what I
> currently have one feed line will be 278' and the other will be 140'.
> >
> > Thanks
> >
> > Rich - N5ZC
> >
> >
> >
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