Secrets to Successful DFing
By Frank N. Haas, Major, CAP © Copyright 2002 – All Rights Reserved

Follow this checklist exactly and you will always find the target:
Assemble the unit properly. (Antenna attached to cable. Cable attached to receiver.)
Turn unit on to REC mode. (Do a battery test every once in a while.)
Set FREQUENCY control to correct frequency. (121.775 for training. 121.500 for ELTs.)
Set SENSITIVITY to FULL CLOCKWISE.
Set VOLUME to desired level.
In REC mode, turn 360° watching meter for highest reading.
Facing direction of highest REC mode meter indication, use SENSITIVITY control to set meter to mid-scale reading (if possible.)
Switch to DF Mode.
In DF mode, turn 360° watching meter for CENTER indication.
Determine which of the two center indications is the right one.
Note bearing of centered meter indication (looking through the antenna.)
Plot the bearing on a chart or map.

Remember these important rules:
(1) Trust your equipment. You will not SEE the target until the DF unit takes you to it.

(2) Set SENSITIVITY to a centered meter indication in REC Mode before switching to DF Mode. This is ESSENTIAL to success. As you get closer, less and less SENSITIVITY will be needed.

(3) Ignore environmental conditions like power lines, power poles, buildings, fences and so on. Don’t listen to the thousands of “old wives tales” and myths others tell about their DF adventures. Nearly all of them are UNTRUE and TOTALLY wrong. As your skill improves, you will understand better how the environment affects the performance of the DF unit.

FAQ (Frequently Asked Questions)

Q: Do all ELT signals have the sweep tone?
A: No. An ELT that is not working properly will transmit a QUIET signal known as a “dead carrier” that can be DF’ed easily. The sweep tone is included with the signal to make the signal easier to identify but the sweep tone is NOT needed to successfully DF an ELT. Extra care is needed to be able to identify a dead carrier ELT signal. Many DFers are fooled by the silent but still present signal.

Q: Someone told me that power lines can make it almost impossible to locate an ELT. Is this true?
A: Generally speaking, NO! Electrical noise emitted from power lines can make it more difficult to hear an ELT signal. The noise, a continuous buzzing sound, can sometimes be so strong that it covers up the ELT signal. To overcome this problem, you have to get closer to the location of the ELT in order to hear it well enough to DF it. This may require the assistance of an aircraft overhead to help guide you in closer. Note: You will hear the continuous buzzing sound in many locations when DFing in urban areas.

Q: How do buildings and large metal objects affect DFing? Someone told me that buildings can mislead the DF unit by creating something called Reflections.
A: ELT signals are just like other VHF radio signals. Signals are strongest when there are no obstructions between your receiver and the transmitter. Buildings, metal fences and other large metal structures can affect how signals radiate or bounce around. Radio signals of all sorts can bounce off or REFLECT off metal or other solid surfaces. These reflections can “fool” the DF unit temporarily. That is, the bearing to the signal might appear to be 90 degrees or more away from all the other bearings taken so far that point in a certain direction. Reflections can be dealt with easily by moving to another location that is on the other side of the obstruction and taking another reading. If the bearing continues to point in the odd direction, move again and verify your readings. You will likely find that the bearings start pointing in the original direction again.

Q: Why is the SENSITIVITY control so important?
A: This control, more than any other, affects the behavior of the DF unit. Improper use of the SENSITIVITY control has more effect on your success than anything else. Too much sensitivity will cause the DF unit to lie and point you in the wrong direction. Too much SENSITIVITY will overload the receiver with signal and the meter indications will be confusing and incorrect. As you get closer and closer to the transmitter, you will prevent OVERLOAD of the receiver by making sure the SENSITIVITY control is set so the meter reads mid-scale in REC mode.

Q: What about those Pizza ovens, toasters and other odd signal sources we hear about?
A: It’s true that some odd devices do generate signals that can be heard on DF equipment. These instances are VERY rare. Such signals are often dead carriers or buzzing sounds. They never have the sweep tone. Trust and believe only a known expert DFer who tells such a story.
Contact Major Frank N. Haas anytime at 386-677-7272 (voicemail #1) with any other questions or requests for assistance.

Secrets to Successful DFing by F. N. Haas, Major, CAP © Copyright 2002 – All Rights Reserved Page 2 of 2