[TowerTalk] Birds and the Leaning Tower

Thu Aug 4 12:14:35 EDT 2016

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 at casair.net>
> To: <towertalk at 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 at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk