[Fourlanders] 6 Meter Antenna Plans For 2008

Sat Feb 16 17:16:57 EST 2008

Great idea Dick.  I have heard of this software but I always thought that it
was primarily for HF but from your email I guess it works for 6 also.  I
will definately look into that.  What I would really like to do is what K8GP
does.  They have TWO sets of stacked beams on 6 with one set much lower that
the other if I recall correctly.  Dick, can you make us another pair of
those beams?  Just joking.

73
Jim, W4KXY 

-----Original Message-----
From: Dick Hanson [mailto:dick at dkhanson.com] 
Sent: Saturday, February 16, 2008 8:15 AM
To: wa4kxy at bellsouth.net; Fourlanders at contesting.com
Subject: RE: [Fourlanders] 6 Meter Antenna Plans For 2008

Good morning all....

Jim...all good thoughts and ideas, so here are a couple more.
If any of you have experience with Terrain Analyzer by Dean Straw, I would
highly recommend taking a look.
It is free software in one of the arrl books. The point of it is to plot
takeoff angles from your specific qth. Of course, you need some rough topo
data to do it, but not an impossible task..

The second part of the exercise is to then employ HFTA again, but this time
you input data like how many elements are on each ant, the direction you
wish to analyze and finally, the height of the ants.

When you push the calculate button, the software draws a graph of what your
lobes look like and over what takeoff angles you are getting max gain.

This is one of the main "tools" used by contesters and dxers. I was only
made aware of it about a year ago, and as a result, have plotted everything
imaginable from my new qth for all my towers and ants from 40-6 meters.

What is interesting is what happens on 6 when you start lowering the stack.
The takeoff angles go higher and change your lobe concentration from
long-haul dx angles of 1-5 degrees down to US 0ne and two hop angles.

For my qth, a pair of 5 ele ants like yours should play very well at 10' and
25'.

Anyhow, I'd sure get a copy soon and start playing.

Ciao,
Dick

-----Original Message-----
From: fourlanders-bounces at contesting.com
[mailto:fourlanders-bounces at contesting.com] On Behalf Of Jim Worsham
Sent: Friday, February 15, 2008 10:41 PM
To: Fourlanders at contesting.com
Subject: [Fourlanders] 6 Meter Antenna Plans For 2008

Hello everyone.  I have been chatting with my 6 meter partner in crime,
W4ATL, about the 6 meter antenna configuration for 2008.  I would like to
share some of our thinking with the group and hopefully get some helpful
feedback and ideas.

This all got started last year with the March/April 2007 issue of NCJ
(National Contest Journal).  That was the Special 6 Meter Contesting Issue
(a recommended read for everyone) and it contained a paper "Control of
Take-off Angles for 6 Meter Es" by K3LC.  In the paper he used EZNEC to
analyze two approaches to raising the take-off angle for six meter yagis.
One was to physically tilt a single yagi upwards and the other was to use
two stacked yagis and feed them 180 degrees out of phase (aka BOP).

Sherman and I have always felt that we aren't getting everything we would
like out of the stacked pair of beams we are using now.  They work great for
the long haul multiple hop stuff as you would expect but we believe that we
are missing contacts on the short single hop stuff closer in.

We did some experimentation last year with a loop antenna as well as a yagi
sitting on the ground and physically tilted upwards.  Frankly, the results
were not good for either approach.  Reading the article you will see why.
It turns out that tilting a yagi physically upwards does not "point" the
main lobe as you would expect.  Instead, it enhances existing vertical side
lobes in the pattern making them dominant but with much lower gain than the
main lobe when the beam is horizontal.  As the beam gets closer to the
ground the loss of gain gets worse!  My guess is that our tilted beam on the
ground had very little if any gain.

In contrast, the BOP approach worked well raising the take-off angle for a
stacked pair of beams from 5 degrees to 22 degrees with just a 3 dB loss of
gain.

The one thing that K3LC did not investigate is controlling the take-off
angle by varying the height of the beam.

So, were am I going with all of this?  For this year I would like to
continue our efforts in finding some way to obtain a higher take-off angle
on 6 meters when needed.  There are three approaches that Sherman and I have
discussed.

First, throw money at it.  There is a product called a stackmatch sold by
array solutions (http://www.arraysolutions.com/Products/stackmatch.htm).  It
would allow us to operate each beam in the stack individually as well as
feed both in phase (BIP) and out of phase (BOP).  Really slick but pricey.
I estimate around $500-600.

Second, have Robin, K4IDC build us a sidearm mount for the 6 meter tower and
mount a single, rotatable yagi at some relatively low height (15 - 20 feet).
I believe that we can scrounge the rotator, feedline and yagi so the only
cost would be the sidearm mount and I am sure that Robin will give us a good
deal on that.  I am not certain how well this will work though.  Intuition
tells me that the take-off angle will increase the closer to the ground the
beam is but I don't know what effects on sidelobs, gain, etc. will occur.
Is there someone on here who is comfortable with EZNEC who can investigate
that?

Third, make our own BIP/BOP switch.  It seems to me that all it would
require is a high power DPDT RF relay and a half wavelength of coax.  It
doesn't have to be pretty or particularly well made.  It only has to survive
the elements two weekends a year.  We could put the relay and coax rolled up
in a tupperware container for example.  A two conductor cable to a switch
and 12 VDC wallwart in the trailer finishes the setup.  Not as slick as the
array solutions stackmatch but the cost is potentially almost zero if we can
scrounge the relay, coax, etc.

So, what does everyone think of these three ideas?  Anyone, have any better
ideas?

73
Jim, W4KXY

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