W3LPL has a lot of Beverage information in his low band presentation.
http://www.k3lr.com/Dayton/Dayton2016/w3lpl.pdf
John KK9A
kq2m wrote:
I want to supplement my transmitting antennas with the most useful
low-noise low-band receiving antennas possible that I can put up in
dense forest and with extremely challenging topography.
My qth and surrounding woods are on a hilltop with extensive and steeply
angled jagged ledge, many ridgelines, ravines and wetlands and areas of
standing water and marsh, varying in height from ~ 750' - 820' ASL.
Past where I would be able to put receiving antennas, there are very
sharp dropoffs to South and West of several hundred feet. It is
beautiful but NIGHTMARISH to walk through the woods under the best of
cndx (like today) but it is a true HORROW SHOW when all the thorns
bushes and dense vegetation is growing rapidly and the Deer Ticks and
mosquitos are everywhere. It's even worse in snow as the ledge and rock
slopes become exponentially more dangerous to access and there is ledge
EVERYWHERE.
Complicating matters are areas of the woods that resemble the moguls on
a ski slope only more spread out. Some of these moguls can approach 30'
high with the ridgelines even taller than that. While they somewhat run
in the same direction ENE to WSW others run on steeply sloping hills
like a series of "steps". One ridge runs North to South on the side of
a hill; drops 15' feet then there is a another ridge then another drop
of 15' or so to a ravine and standing water and muck pond about 20'
across. And there are flatter areas of ledge that have what appears to
be a boulder on it about 5' high and 30' long right in the middle of a
flat spot. There are a few formations like this in other areas as well.
The result is that there are very few areas open for more than 100' in
any direction without running into these rock formations and steep hills
and dropoffs.
Now that I have described the terrain, my questions will make more
sense:
1) Is that a formula specific to beverage antennas for determining
length? Or should I used the standard dipole formula 1/2 wavelength =
468/ f?
2) What is the effect on a terminated directional beverage (terminated
at the back end that runs downhill at an 8% slope? If the maximum of
the lobe is at say 15 degrees on flat ground, does the lobe maximum drop
to an even lower angle? Or does the lobe change? or both?
3) Same question but with the beverage now running uphill at a 5% slope.
4) Same question but with a 20' high "Hump" in the middle? as the
beverage starts and is terminated on a flat spot, runs to the top of a
ridge and then back down again on the other side.
5) If you put a phased array of verticals NW to SE (with pattern
broadside to the direction of the elements - receiving NE) in a flat
spot that then points directly into a 30' high ridge to the Northeast
50' from the front of the array, have you essentially turned a low angle
receiving array into a created a high angle receiving array?
6) What happens when you have 4 ground mounted receive verticals with
that large 5' boulder taking up of the space in the middle of them?
What does that do to the pattern?
7) Let's say that you have a 6 L array of receive verticals in 2 rows of
three with each line pointing NW to SE (pattern broadside NE) and they
are phased. But instead of being on flat ground However, they are on
the side of a steeply sloping hill so that the first row is at 820' asl
and the 2nd row is in the same direction but at 800' asl. How might
that affect the pattern? (for purposes of this question ignore the
impact of ground being "ledge" rather than soil.
8) Now lets say that you have transmitting antennas for 160, 80 and 40
nearby. How far do the receive verticals and beverages have to
physically be from the radials of the 160 Inv L, 80 M 4-square and from
the 40 meter wire beam before the performance of either the transmitting
antennas or receiving antennas starts to degrade? A formula for
distance in wavelengths would be most helpful.
9) How far apart fractions of a wavelength do the beverages have to be
from each other before their performance starts to degrade?
10) What is the impact on beverage receive performance if the RG6 Quad
Shield coax to the shack instead of running along the forest floor,
instead runs horizontal and parallel to the beverage? I am thinking of
keeping it elevated to greatly reduce the opportunity of critters to
chew on it but I don't want to impact the performance of the beverage.
11) Is there any performance advantage if I were to terminate the
beverage with a ground rod and radials in that standing water on the
hilltop? Or does it not make a difference?
Finally, I have read about many preferred beverage lengths for 40, 80
and 160 but few if any seem to be based on an established formula to
calculate their lengths. What formulas and multiple of wavelengths
would you use and why?
12) How many wavelengths on 40 is too long and how many is too short?
Same question for 80? Same question for 160. I know that these answers
vary by band which is why I am asking.
They are challenging questions that are not really covered in anything
that I have read. I would appreciate all of your thoughts and insights!
Tnx & 73
Bob, KQ2M
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