Topband: Steeply Sloping Ground

[Guy Olinger K2AV]

Glad to have been of service.

The way you model an antenna on a slope, is to SLANT the ANTENNA the
same as the angle of the slope, if it's actually pulled true vertical,
and then print out the plot.  On the plot draw a line through center
at right angles to the antenna's vertical.  Anything below either the
printed base line or the one you drew is lost to dirt, whether near or
miles away, but you will see the effect on low angle vertical
polarized signal with a distant horizon.

Slanting the entire antenna is very easy in EZNEC... Main
panel:options:angle convention:compass bearing. Put your directivity
toward the Y axis. When done entering and have it right, do...  Wires
window:wire:rotate wires.  Enter the angle between your hillside slope
and the vertical construction axis.  Set axis to "X".

It is a royal PITA to do that, but probably the only way to see what
is going on.  Or use a protractor pressed to the screen of the EZNEC
display.

I will continue to urge that cross slope aiming on that most fortunate
location is wasting results.  Going flat just throws away a supreme
advantage which most people don't have.

Comparing your antennas will be a very difficult proposition with many
traps which can give you completely opposite results from true.

73, Guy,

On Thu, Jul 28, 2011 at 12:47 PM, Charlie Young <weeksmgr at hotmail.com> wrote:
> Guy, my major local noise sources are power lines, which are located below
> me.
>
> Your observation about the transmit antenna hearing better than the rx
> antenna is true to the NW and to the SW.  For the most part, these two
> inverted L's consistently hear better than any rx antenna we have tried.
> However, my beverages/flags for these particular directions were compromised
> by routing/placement and these are two directions we hope to improve this
> year.
>
> To the NE, which is one of my best directions, a 450' beverage running
> partially sideslope and partly downslope is a major improvement in RX over
> the NE inverted L.   Likewise, a 60 degree dual flag that was running
> sideslope was a major improvement over the L and nearly equal to the
> beverage.
>
> I think the dual flags offer the best chance for significant rx improvement,
> especially in my problem directions where running a good beverage is
> difficult to impossible.
>
> Let me be specific with this question.  I have modeled the dual flag
> in EZNEC 2+ over level ground, and see the elevation response pattern.  By
> installing the antenna over sloping ground in the target direction, do you
> think the modeled elevation response will in practice shift down toward the
> horizon and, if so, which configuration of the antenna will maximize this
> effect?  A level antenna at unequal height over the ground or an antenna
> tilted down from the horizon, but parallel with the earth surface.  My
> suspicion is the tilted antenna would have the lowest elevation response but
> I am not sure.
>
> Guy, I really appreciate your response to my question.  We have followed
> your postings over the years, and I have great respect for your experience.
>
> 73 Chas N8RR
>
>> Date: Thu, 28 Jul 2011 12:02:55 -0400
>> Subject: Re: Topband: Steeply Sloping Ground
>> From: olinger at bellsouth.net
>> To: weeksmgr at hotmail.com
>> CC: topband at contesting.com
>>
>> If you are in a quiet location, you may find it difficult to hear
>> better than your TX antennas, simply because they are not
>> disadvantaged by the normal issues over flat ground. Vertically
>> polarized signals do not bounce well off dirt. Essentially not at
>> all, even with the best dirt found around. For most people dirt and
>> clutter obscure the lowest angles, for ANY antenna.
>>
>> Your hearing well in a particular direction will have a lot to do with
>> NO CLUTTER or obstruction in your way at the lowest usable angle.
>> That is why aiming a direction sideways across the hill to have level
>> ground in front of it is not a good idea. If I understood your
>> terminology correctly, beverages aimed downhill did best. You will
>> find that to be true with ANY RX antenna, as the no obstruction
>> quality of looking in the clear at a very distant horizon will trump
>> any other consideration.
>>
>> Modeling beverages, flags, pennants, yada, yada, all of them
>> significantly improve pattern up 10 or 15 degrees vertical. This
>> angle is formed above the immediate ground slope.
>>
>> At your QTH, it may not be possible to improve over 280' downhill
>> beverages. Placing two of those (or two of anything) aimed downhill,
>> equal phased side by side for best horizontal pattern may be the best
>> possible.
>>
>> 73, Guy.
>>
>> On Thu, Jul 28, 2011 at 10:58 AM, Charlie Young <weeksmgr at hotmail.com>
>> wrote:
>> >
>> > I am about to configure antennas for my 3rd Topband season here in WV.
>> > The terrain is very irregular.  My house sits atop a conical shaped hill,
>> > with sides which slope off steeply in all directions.  All of my transmit
>> > antennas are on top of the hill, overlooking the steep slopes including the
>> > 160 inverted L's, which are configured with the vertical portion of the
>> > radiator right at or just over the cusp of the hill, with the ground falling
>> > away steeply in the desired direction.  Last year, I used four of these L's,
>> > each positioned to cover a direction favored by sloping ground.  Switching
>> > between them exhibited noticable directivity on rx and tx, so I am convinced
>> > we are on the right track with the tx antennas.
>> >
>> > I am not sure what to do about the rx antennas.  They can't be placed on
>> > the high ground, due to space and driveway constraints.  The first season,
>> > we tried several short beverages and last year we added four  dual flag
>> > antennas.  There are not many options for the beverages.  To cover desired
>> > directions with my property layout and the terrain, these must be placed on
>> > the sides of the hill, some running upslope, some downslope and some
>> > sideslope.  They seem to work OK, some directions better than others.
>> >  Generally, I found that an upslope beverage is the poorest performer.
>> >
>> > My real question regards the best way to orient the flags in relation to
>> > the sloping ground.  I have some choices.  In some cases, we can go
>> > sideslope, so the antenna is both level and parallel to the ground surface
>> > in the primary target direction.  In other cases, I am faced with the choice
>> > of either making the antenna array  level, which puts one end significantly
>> > higher above ground surface than the other or placing the antenna array
>> > parallel with the earth surface, which makes  the whole array tilt downhill
>> > in relation to the horizon.
>> >
>> > The  flags I am using are 21' high by 30' long, thus making the double
>> > flag array about 63' long.
>> >
>> > My intuition with these antennas says to avoid putting one upslope
>> > entirely, and when possible to make it sideslope.  However there are some
>> > directions where we must go downslope, and my instinct is to follow the
>> > earth surface and have the array tilt down in relation to the horizon.
>> >  Anyone got any experience with this, or any thoughts about it making any
>> > difference in the real world?
>> >
>> > 73 Chas N8RR
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > UR RST IS ... ... ..9 QSB QSB - hw? BK
>> >
>