PSR-1 sensor

[gerard-sog]

Theory of Operation
The geophones have a resonant frequency around 5 to 20 Hz which for practical use is below human hearing. They pickup the sound of the earth shaking as caused by people walking, vehicles with engines, and most of all helicopters nearby. Inside the PSR-1 a circuit translates the subaudible frequencies into a range that can easily be heard.

The geophones can easily be hidden and the simplest way is to bury them underground along with the WD-1 phone wire that connects them to the main unit. Attaching a sensor under a suspended floor or bridge provides mechanical amplification of the sound. The poorest place to put a geophone is on concrete. Vertical orientation seems to work best for most things.

Unlike all the other systems that use geophones this one lets you hear the sounds. In the other systems there is an alarm, but when it goes off you don't know if it was an animal, one person, or a division. The benefit is that those systems can be set and left alone.

The label says:
AN/PSR-1
DETECTOR, SEISMIC INTRUSION
MODEL X-150A
STOCK NO. 6655-903-0932
PT NO. 87990-5133-000-0001-2
CONTR NOm-73280 SER. NO. T-17
MFR: 18667

An email from Mike M. says his data plate reads:
AN/PSR-1A
DETECTING SET, INTRUSION
STOCK NO. 6655-880-1997
CONTRACT NO M00027-68-C-0079
SERIAL NO. A16x
MFR 14056
U.S