Field Intensity-Measurements In the Nulls of a Directional Antenna Pattern

Field intensity measurements in the nulls of a directional antenna array can often be confusing particularly if one fails to observe the direction of wave arrival as being truly from the transmitter and desires to orient the loop antenna on the meter accordingly. In a deep null of the transmitted pattern, use of a field intensity meter as a direction finder can lead to gross bearing errors. Rotating the loop for a null indication will frequently result in an apparent bearing error closeito 90°when the instrument is viewed as a direction finder. The question arises as to whether the actual field intensity reading should be taken as per the instruction book, the loop oriented for maximum indication, or taken with the loop plane pointed at the transmitter irrespective of the direction of maximum indication. This paper will explain the basic D.F. bearing phenomenon, along with a unique experiment to confirm it, and will point out why the loop must be pointed strictly toward the transmitter regardless of the direction of maximum indication in the event the two bearing choices disagree.