Keeping birds away from antennas is similar to keeping them from
perching on boats and "messing" on the decks or ditto in outdoor retail
building material sales. Our Lowes uses recordings of bird screeches
of, I believe, predator birds. Yachties down at the yacht club or
marina use rubber snakes and or plastic owls. My observation is that
snakes and owls work for a while but the effect wears off and eventually
the owls will be perched on and pooped on. I have used ultrasonic
emitters to keep pests away but you might have a problem with cats and
dogs who hear the ultrasonic signals. Of the commercial units I have
purchased (some good ones from "The Sharper Image") some have a
selection switch that has a "PET FRIENDLY" position. Some units can
select for random emissions which work better over time as the culprits
don't get used to the sound.
DIY is pretty simple. You need some tweeters/projectors that will get
into the ultrasonic range efficiently and an oscillator running
sufficiently above human hearing so no one (except the birds) is
annoyed. No need for linear amplification, Hi Fi is not required.
In the olden days when 555 and 556 chips were popular some simple timer
ckts would provide an ultrasonic oscillator that is swept in freq to
give an ultrasonic "yelper." Feed this to a high output buffer (or amp)
and that into the speakers.
When I lived on Point Loma in San Diego I used to have folks walking
their dogs in the early A.M. that would let their pet go a leash length
into my yard to leave a "love note." An IR motion detector to switch the
ultra sound on solved the problem. One morning along came Mr.
Unsuspecting with his German Shepard. The IR was adjusted to see
targets off the sidewalk into my front yard. The dog got a BIG Blast of
ultrasound and recoiled from it so forcefully it spun the owner around
dropping him to one knee and nearly dragging him into the street. The
guy just thought his dog was having a fit (I guess he was, just not
without a little help.)
I think ultrasound properly administered would keep birds away from an
antenna. The lab where I worked had a problem with seagulls "messing"
all over above water instruments on an oceanographic tower. They
(working within the limits set by SPCA) recorded the cries of a
distressed gull and played them repetitively over a PA system. The
local gull population was freaked out for a while and avoided the tower
for a while but over time just got used to hearing one of their cousins
"tortured" and effectivity went down.
Enter ultrasound... Sufficiently loud noises makes birds want to be
somewhere else. Ultrasound doesn't bother people, just animals who can
hear it. If it is sufficiently above human high freq hearing limits but
not out of the hearing range of the intended targets it can be very
effective. In my 20's I could hear 20,500 Hz in one ear and 21,500 in
the other. I could hear bats feeding, ultrasonic burglar alarms, left
turn sonar detectors for traffic light controls. I would recommend
going up higher, maybe around 25000Hz if there are any young folks
around. Mount the projectors well above ground and aimed up to minimize
field strength where people and pets would get ensonified. With
sufficient volume the birds will just not want to get in the sound
field. Since a large bird can cause damage as soon as it lands, random
emissions are not advised. You need continuous coverage to prevent
birds from landing.
There are other deterrents but the legal status of LASERs that would
cause uncomfortable heating and or visual disturbance might give me
pause to recommend any specific approach. You can buy LASERs on-line
that will pop dark colored balloons from several yards away.
Good luck,
Patrick NJ5G
On 8/2/2016 11:51 PM, Jim Thomson wrote:
Date: Tue, 02 Aug 2016 10:31:34 -0400
From: Dave Leisman <w8qwdave@casair.net>
To: <towertalk@contesting.com>
Subject: [TowerTalk] Birds and the Leaning Tower
Got a very different question for the group. I have a couple of very large
antennas, one a 3 element 40 meter yagi and the other a 3
element full size 30 meter yagi. My problem is the birds which hang around
these antennas. I realize the antennas are a great place
for birds to land and scope out prey below, but the other day a rather large
bird tried to land on the end of one of the elements of
my 40 meter beam and bent it down almost to a 90 degree angle. Now I can either
take the antenna down (no small job), fix it and re-
raise it, or I can hire a manlift (no small expense) and do it mid-air myself.
Does anyone have any suggestions how I might keep the birds away from my
antennas so I can avoid this kind of hassle in the future?
Thanks in advance.
Dave, W8QW
## did the entire 40m ele rotate on the boom.... or is the tip permanently
bent down 90 degs ??
If the tip is bent down permanently, the tip is not strong enough. If designed
right, you should be able to load
the eles and tips with ice. The worse that will happen is the tip will deflect
straight down at a 90 deg angle. When the
ice falls off /melts, the tip will spring back up. If the tips are made from
something like .375 inch OD x .035 wall,
replacing the tips with .058 wall should do the trick. But you would also
have to look at the next inboard section of
tubing as well. By using thicker wall tubing / and /or doublers inserted
into the weak sections, you can substantially
increase the strength of an ele, without adding a lot of weight.
## I noticed that birds sitting on the tips of els are not fazed in the
least... when 1-2 kw cxr applied to the yagi. One would
think with the extreme high RF voltages on the tips of a yagi, that the birds
would fly off, they dont. Years ago, I had a
204BA sitting on wooden sawhorses..and applied a 600 w cxr to the yagi. I
could light up a florescent light tube full tilt,
when the 4 ft tube held parallel to either tip of the DE..and several inches
away.
## http://www.k6jrf.com/k6jrf_BS_Repair.html here K6JRF uses bird
spikes to get rid of the bird problem.
click on any of the pix to see a close up of what bird spikes look like. he
used em end to end, across his 75m rotary dipole.
End of problem. It’s another option.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|