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6 Answers

VOT VOR Test Facility

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Flight Instructor, Private Pilot

When we are testing our VOR's on the ground to a VOR TEST FACILITY (VOT)  why does it not matter what position our airplane is on the airport in relation to the VOT?  I understand it only emits a radial beam on the 360 degree radial, and that we tune our OBS knob to 360 FROM or 180 TO for the indications.  


Is the VOT using the same facility as the VOR if the VOR is on the airport?  (i.e. KMKC)  Just a different frequency?

6 Answers

  1. John D. Collins on Mar 02, 2011

    This is not a precise detailed technical explanation, but hopefully you will get the idea.  The VOR transmits two signals, one is a reference signal and it is transmitted in all directions.  The second signal is encoded with the radial by using a phase shift. The phase shift signal is transmitted in only one direction for each radial with the direction and phase matching each other.  The aircraft receiver receives both signals, the reference and the radial phase signal.  The difference in degrees between the reference signal and the phase signal is the radial.


    In the case of a VOT, it transmits the reference signal and the phase signal for the 360 degree radial in all directions, so regardless where the receiver is, it will only detect being on the 360 degree radial.  Selecting 360 degrees as the VOT test radial makes sense because it means that both the reference signal and the radial phase signal are the same phase and it makes the VOT simple to construct.  I don’t know for sure, but I doubt the VOT would be housed close to an on field VOR, if for no other reason than to avoid interference.  I suspect it is a box in the communications equipment room somewhere on the airport.

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  2. Ben on Mar 03, 2011

    Awesome explanation of VOT here – with visuals, also if you prowl around the rest of the website you’ll find many other useful animations and explanations:

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  3. Curtis Ide on Mar 05, 2011

    John gave a great explanation of VOT’s for you I just wanted to make an add-on question/answer.  I don’t have access to the Airport Facility Directory for your area today but I wanted to make sure you are using a VOT versus a VOR Ground Checkpoint.  If it is a VOR Ground Checkpoint on the field it will be listed in the VOR Checkpoint tab of the AFD and you will find a circle with an arrow inside located on the field.  In that case you would also be testing for a specific radial for that location not just the 360 and that radial would be located in the AFD as well.  In addition, many avionics maintainence facilities have a VOT box they can use to test the equipment in the shop and we have used them before to get a check in when the aircraft hasn’t flown in a while (we don’t have any other ground points on the field).

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  4. Bill Dixon on Jun 08, 2011

    If you are identifying a VOR and hear T-E-S-T can you use that station?

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  5. Kent Shook on Jun 09, 2011

    No. Any navaid broadcasting T-E-S-T is undergoing maintenance and the signal may not be correct, even if you are receiving it. See AIM 1-1-12.

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  6. Timothy on Apr 25, 2015

    I’m trying find the nearest VOT test airports that are located here in NE Ohio. I know, check the AFD. I wonder if they are phasing them out. KCAK use to have one.

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