[CQ-Contest] Stacking on separate towers, take off angles?

[Jukka Klemola]

2013/3/14 Pete Smith N4ZR <n4zr at contesting.com>:
> I think that someone did some work maybe 10 years ago on the theory (and
> practice) of feeding two antennas on different towers.  IIRC, the process

It was Eric K3NA.
Great analysis, showing by simulations the deep nulls do not come into reality.

I think parts of Eric's work might still be on NCJ website.

..googled a bit; you can sart for example here:
http://www.ncjweb.com/Ant_Interact_Part_6.pdf

...
> Jukka's solution sounds like it worked out very well for him, but I think
> that he was pretty lucky.  More years ago than I'll admit to, I had a
> college astronomy course where I had to manually calculate the broadside
> pattern of a 22 MHz interferometer that used two dissimilar yagis pointed
> perpendicular to a 1500-foot baseline.  Much trig later, I had a pattern of
> many very narrow beams with deep nulls in between.

Yes. Your calculations are correct.
It is to be noted, my system has some intentional dissimilarities plus
it sees a pretty uneven terrain to any direction .. yielding a sum of
the waves that does not really create these nulls on 40 nor 20.

I did not comment too much of 15 & 10.
My experience is the nulls seem to happen there.

I have not analyzed why that is - or seems.



> My point is that in
> terms of the phase of signals being emitted from two antennas on 20 meters,
> 65 feet is pretty near a full wavelength, and depending on the angle of that
> baseline to the desired direction, the signals will arrive at the target
> with very different phases, some reinforcing and some cancelling.

I cannot really see this.
I was expecting, but nope. Nothing major noticed on 40 nor 20.


> A final comment - in Europe I can see front-to-back and front to side being
> of major importance

Oh yes.
My 20m toy creates a silent EU when using to North America or JA directions.

Problem was I had to take a sample from the TX line and feed a little
to EU so they can hear me .. it reduced the amount of people coming to
call CQ on the same frequency I was already using.


> - I'm not sure that's quite so important in VE9.  I'd
> much rather have the broader vertical pattern and pattern options that a
> conventional stack affords, but you gotta run what you have.   And Mike, you
> might want to check the archives of the Towertalk reflector, an excellent
> source for smart practical antenna advice.
>
> 73, Pete N4ZR

Oh yes.
The factory-made antennas are sometimes OK as instructed.

More often you need to get some tips how to make them last longer or
perform better.

Have Fun moments building your setup.
Remember, every learning is Fun.
Those are the moments you have to re-do something.


73,
Jukka OH6LI