Ultrasonic Pest Repellers

The microphones and mic preamp of a phone probably reduce frequencies above 4kHz then are poor ultrasound (>20kHz) detectors.

I took a picture from a shed which the pigeons nested in it. The arrows show the muster points of pigeons which are almost unreachable for us. For this reason we can use only ultrasonic as a repeller.

Experimenting with two ultrasonic transducers (38kHz), I discovered that the sound is strongest at a close distance, and along the center axis of the transducer.

I don't know if your transducers work in a similar fashion. Seeing the large area under your roof, I suspect they might repel pigeons within a few feet. Greater voltage ought to produce louder sounds but there's a risk of breaking it.

Was the idea of balloons mentioned yet? Float helium balloons shaped like owls up to the roof. Your shed appears open to breezes which would send the balloons bobbing about. The helium will need a recharge every few weeks. As an alternative, hang balloons from the joists, to bob in the breeze.

BradtheRad said:

Experimenting with two ultrasonic transducers (38kHz), I discovered that the sound is strongest at a close distance, and along the center axis of the transducer.

I don't know if your transducers work in a similar fashion. Seeing the large area under your roof, I suspect they might repel pigeons within a few feet. Greater voltage ought to produce louder sounds but there's a risk of breaking it.

Was the idea of balloons mentioned yet? Float helium balloons shaped like owls up to the roof. Your shed appears open to breezes which would send the balloons bobbing about. The helium will need a recharge every few weeks. As an alternative, hang balloons from the joists, to bob in the breeze.

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Thank you.
As friends said and after some Q&A, I think ultrasonic is not the only and best way for repelling the pigeons. As you see in the picture which I have taken, The trouble is that the muster points of the pigeons are not reachable for us!!!

Seeing your photograph, the barn is so large that birds have ample places to roost at a distance from 4 ultrasonic devices. Unless you install about 20 of them.

I imagine a ceiling joist blocks such sounds. So if a bird hears noise on one side, she finds a quiet spot on the other side.

There might be gases that rise upward and are noxious to pigeons. Ozone? Chlorine? A gas generator could operate on the floor while the gas rises to the ceiling. You'd need to install panels about a meter high at the top of openings in the structure.

A 'jacob's ladder' produces ozone from sparks and also creates repeating loud static.

Or odors? Example, peppermint, cinnamon, cayenne hot pepper. Seen at this website:

smithspestmanagement.com/blog/post/how-to-get-rid-of-pigeons/

An odor dispenser might be copied from room fresheners run by electricity which produce a fragrance from oil (essential oils or similar).

I think they are laughing at me

Quadcopters or drones...
They're always doing more fantastic things. A swarm of them can be programmed to fly in formation, avoid obstacles, disperse and regroup, etc.

Maybe one quadcopter is all you need in your shed. Do any of your team enjoy this sort of thing? New models keep coming out with unbelievable capabilities... Automatic decision-making, ability to sense surroundings, to chase moving things. To return to its charging base before the battery gets low.

One quadcopter might tour around pigeons' favorite roosts. Sensing a pigeon's presence, it flies near to flash a light, buzz ultrasound, squirt water.