Expert: Marc Ebelini - 4/18/2005

Question
Dear Sir:
Would you please explain me the following abbreviations and introduce me some sources especially internet resources on these topics:
1- ECCM
2- VOR
3- IFF
4- FDR
Thank you very much!


Answer
There are numerous abbreviations and fortunately I know the first three. It started out as ECM, which means “electronic counter measures” that are used for countering electronic devices like a Radar lock on a target. The ECCM is for “electronic counter counter measures” this device is to counter the counter measure. Every time someone comes up with a system to counter a device then another system is devised to negate it. This classified information.

VOR “ Vhf Omni Range” some times called visual omni range because the navigation information is visual instead of aural. This was because prior to the VOR system navigation was accomplished aurally using the Adcock range system. That should give you a clue that I am an old timer. The signal consists of AM and FM modulated signals. The reference signal is FM and the AM is used for the radial information. Using a goniometer the AM signal rotated at 1800 RPM getting a reference signal each time the AM signal was started at “0” degrees. By timing the AM signal the aircraft indicator will display what radial it was on. The phase comparison will determine the To/From indication because the left/right needle will center on the reciprocal. Flying the course backward will cause the needle to move further away from center as you fly to it. Basic accuracy is +/- 2 degrees. The military used TACAN that was more accurate but used a more complex system. Many VOR stations  later incorporated the DME portion of TACAN. “Distance Measuring System.”
A simple way to explain the VOR. There is a rotating beacon that turns once a minute. When the beacon faces north a smaller omni directional light flashes. If the beacon is seen fifteen seconds later then you will be at ninety degrees. Thirty seconds, one hundred eighty degrees. Each second equals one degree.

IFF “ Identification Friend or Foe” started out as a military device. It is now called a transponder. The IFF unit had only 64 codes the current transponders have 4096. It's an octal numerical system having four digit windows each going from 0 to 7. Traffic control centers interrogate the aircraft with its radar signal requesting a response. Aircraft having a transponder will respond with the code number given them. Aircraft in distress will dial in 7700 that will set off alarms at the center advising them of the aircraft's condition. When there are several aircraft in the area using the same code the center will request each one to identify themselves. Each device has an ID button that will then transmit an addition code after the first code is sent. The controller then sees that aircrafts response to flash on the screen.

You got me with the FDR. I will have to look into this. Is it an airport identifier? They are not always logical like Los Angeles is LAX. Only JFK matches the name that comes to mind. Not an airport, give me a clue.

To learn more about the above subjects a library would be of help. There are books on these subjects.