The Philadelphia Experiment


U.S.S. Eldridge, July 25, 1943



U.S.S. Eldridge at sea in 1944

U.S.S. Eldridge at sea in 1944



U.S.S. Eldridge at sea April 25th, 1944



U.S.S. Eldridge at sea in 1944



U.S.S. Eldridge at sea in 1944

U.S.S. Eldridge at sea April 25th, 1944




U.S.S. Eldridge at sea April 25th, 1944




Philadelphia Naval Yard, November 1947



Newport News Shipyard, October 17th, 1944

Norfolk Naval Yard – Helena Annex, December 12th, 1944



Norfolk Naval Yard – Portsmouth, December 12th, 1944


Let’s talk about RADAR

Figure 1: radar principle

The electronics principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for a return echo can be roughly converted to distance if the speed of sound is known.

Radar uses electromagnetic energy pulses in much the same way, as shown in figure 1. The radio-frequency (rf) energy is transmitted to and reflects from the reflecting object. A small portion of the energy is reflected and returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object.

Radar is an acronym for

Radio (Aim) Detecting And Ranging
The word „Aim” was inserted during the time of the World War II approximately. Later, it was left out again since RADAR doesn’t concern only aims, however.


The basic principle of operation of primary radar is very easy to understand, however, the theory can be quite complex. An understanding of the theory is essential to correctly specify and operate primary radar systems. Implementation and operation of primary radars systems involves a wide range of disciplines including building works, heavy mechanical and electrical engineering, high power microwave engineering and advanced high speed signal and data processing techniques. Some laws of nature have a greater importance here, though.

Radar measurement of range, or distance, is made possible because of the properties of radiated electromagnetic energy.

  • This energy normally travels through space in a straight line, at a constant speed, and will vary only slightly because of atmospheric and weather conditions. (The effects atmosphere and weather have on this energy will be discussed later; however, for this discussion on determining range, these effects will be temporarily ignored.)
  • Electromagnetic energy travels through air at approximately the speed of light,
    • 300,000 kilometers per second or
    • 186,000 statute miles per second or
    • 162,000 nautical miles per second.


  • Reflection of electromagnetic waves
    The electromagnetic waves waves are reflected if they meet an electrically leading surface. If this reflected wave is registered again at the place of the origin, this is a proof of this that an obstacle is in the propagation direction.


Radar Basic Principles

The following figure shows the operating principle of a primary radar. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal delivered by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

Figure 1: Block diagram of a primary radar

All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays.

Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin which indicates the pointing direction of the antenna and hence the bearing of targets.

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