[Fourlanders] adjusting takeoff angle

Wed Jun 13 22:46:17 EDT 2007

I have a Yaesu 5400 AZ-EL rotor that ya'll can borrow.

Fred N4GER

-----Original Message-----
From: fourlanders-bounces at contesting.com
[mailto:fourlanders-bounces at contesting.com] On Behalf Of Rogers, Ron
Sent: Wednesday, June 13, 2007 12:18 PM
To: Paul Yeager, ABR(R), REALTOR(R); Fourlanders
Subject: Re: [Fourlanders] adjusting takeoff angle

Hi guys,

For those that weren't on the mountain to hear our discussions about
this 6 meter antenna experiment, here is some history.

This W4NH idea started between myself and NX9O a few weeks ago when I
was discussing a 6 meter experiment that we tried at W9ICE in EN60 with
our frustrations of not being able to score 6 meter contacts into
eastern PA and NY where some key population densities were. Brian picked
up on a fact real quickly and pointed out that the areas being targeted
by W9ICE were the same areas targeted by W4NH and, in fact, were about
the same distances.

A quick calculation of our W9ICE easterly take off angle and E-layer
reflective result showed our first touch-down point to be out in the
Atlantic ocean somewhere. So, one of the final W9ICE contests we simply
put a Cushcraft 5 element beam on the ground and pointed it in the
desired direction, then propped it up to about 45 degrees and had a coax
switch back at the station to switch between our 2 antennas. The result
was that we started harvesting more close in contacts (500 miles) using
the antenna pointing upward. It appeared that the 45 degree angle off
the E-Layer (un-enhanced) shortened the first touch down point to about
500 miles out. 

Now, if you add up what we use on Soco Bald on 6 meters (5500'
elevation, stacked 5 element beams, and tight vertical plane take-off)
theory says this is actually detrimental to our desire to put the 18,000
Watts ERP into the high population areas (or even hear the 100 watt
stations calling you) within 500 miles of our location. In fact, it
would suggest that the incident angle to the E-Layer would be even
further out, thus even a longer distance to first touch down point.

If you take a quick measurement of the shortened 500 mile radius from
W4NH desired by us, that would include New York, Philly, Cleveland,
Chicago, St. Louis, Jacksonville, etc. 

If you could view the 6 meter log Sunday evening when there really
wasn't any wild sporadic "E" openings taking place, the suggestion was
made to point the 6 meter beams to the W-NW after they had been pointing
to the N-NE, what did we see started happening ? 

We actually started scoring contacts in the DN & DM grid
areas.......yep, about 1200 miles out. That's why some of us suspicion
we may be overshooting the upper east coast population density using too
high of gain antennas at such a high altitude.

For the elevated antenna experiment we already have a beam lined
up......a Cushcraft 5 element beam not being used right now. We don't
need anything fancy, and certainly DON'T need a lot of gain and
directivity for this experiment.

It's light enough for the Yaesu 5400 AZ-EL rotor and we already have the
mounting figured out......IF we want to do it that way in Sept.

But, the initial plan in Sept. was to simply use the Cushcraft, set its
ass on the ground, point it toward FN21/31 (or EN51-61), then point up
toward 45 degrees, and held there by a inverted "V" wooden frame made
from 2X2 lumber or even wooden step ladder. I have 100' of Beldon 8214
coax and a 2 KW antenna switch to handle the power.

We just think it would make an interesting experiment for W4NH to try.
Who knows. If the theory pans out and validates a few assumptions to us,
it would make a nice case study to present at an upcoming VHF
conference.   

Anyhow, enough rambling about theories for now..........

Ron 
WW8RR

-----Original Message-----
From: fourlanders-bounces at contesting.com
[mailto:fourlanders-bounces at contesting.com] On Behalf Of Paul Yeager,
ABR(R), REALTOR(R)
Sent: Wednesday, June 13, 2007 1:28 AM
To: Fourlanders
Subject: [Fourlanders] adjusting takeoff angle

Ron WW8RR points out that our high-gain stacked beams are likely
striking the ionosphere quite some distance away, due to their low
takeoff angle.  Ron further suggests that this is causing us to miss
closer in stations that we might be able to work, if could arrange a
higher takeoff angle.  (Ron - please let me know if I have misstated
something here)

  I see two obvious ways to change the takeoff angle.

  1) Mount anntenna(s) on an az-el rotator.  This seems pretty simple,
but when one considers the details, it becomes a bit complex
mechanically.  How does one mount a horizontally-polarized yagi on an
az-el rotator?  The only way I can see is to mount it on a rather long
"boom", rotated by the elevation rotator.  The boom needs to be rather
long to avoid interaction between the antenna and the tower/rotator, and
may need to be fiberglass or other non-conductive material to avoid
degrading the performance of the antenna.   This will also place quite a
side load on the rotator and tower, unless the boom is extended to the
side opposite the rotator with a counterweight.

  Alternatively, we  might extend the antenna's boom, then add a right
angle to the rotator.  This increases the load on the elevation rotator
considerably, unless a counterweight is added.

  See what I mean about mechanical complexity?

  2) Using a similar antenna arrangement to the one we used for the
contest, adjust takeoff angle by adjusting the phase between the two
antennas.  Mechanically, this is no more complex than the current
arrangement.  Electrically, it's quite more complex.  Not rocket
science, but certainly more complex than a single feedline running to a
splitter feeding both antennas.

  We could do something as simple as selecting upper/lower/both yagis,
or get more complex and switch sections of feedline in and out to
actually change the phase.  Two switchable sections of feedline would
give us 4 choices of takeoff angle - in-phase pluse three different
phase delays.

  Anyone have any idea how to model phase vs. takeoff angle for out pair
of yagis?  Speaking of modeling...  how about takeoff angle vs. "skip
distance"?

  I suggest that we test the concept using a lightweight 6m yagi, like
the 4 element Comet I have, mounted on an az-el rotator, either during
the September contest or at some time between now and then.  This would
give us an idea of whether or not the concept is viable, and what sort
of adjustments to takeoff angle are necessary.  Once the concept is
validated, we could construct a "phasing system" to use with our pair of
yagis.

  So... what do y'all think?

  73 de W4SKI

Paul Yeager, ABR(r), REALTOR(r)/Broker
Accredited Buyer Representative
Mountain Fever Real Estate
828 400 9442 (cell)
828 926 2545
888 926 2545
828 926 3860 (fax)
paul at mtnlist.com
www.mtnlist.com

What is ABR(r)?  Find out at http://www.rebac.org
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