Bob,
Given your unfriendly terrain, you might consider the Waller Flag
antenna. You could mount one on a short tower with a rotator. From what
I have read, these antennas are capable of very high RDFs with a
relatively small footprint. It consists of two terminated flag antennas
driven 180 degrees out-of-phase. The 180 degree phasing enhances the
front-to-side rejection of the array thereby raising the RDF, which
comes at the expense of output level. The very low output level
resulting from the 180 deg phase shift requires very high common-mode
rejection in the feed system to preserve the RDF and a very low-noise
high gain pre-amp to bring the signal levels up to a useful level. You
can read more here:
https://www.kkn.net/dayton2011/N4ISWallerFlag.pdf
Some variation of this antenna has been on my list of things to try at
my QTH. Hopefully ham radio will still exist when I finally find the time 🙁
73, Mike W4EF............
On 12/4/2021 3:09 PM, kq2m@kq2m.com 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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|