STUPID DF TRICKS

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The tricks listed here are of the "yeah, I heard of that once!" variety.   You may find one or more of these tricks useful in the field someday.   Some of them may be exactly as advertised and sound pretty stupid, but they also might work.   Try one if you think you need it!   Experience can't be taught, but experiences can be shared.  These tricks weren't worth an entire "SAR WAR Story" so they were placed on this page. 

If you tune any FM radio to 100.1, you should be able to hear the ELT when you are very close to it.   This works especially well if you have a cheap FM radio!   The intermediate frequency (IF) of your commercial band FM broadcast radio is 10.7 MHz.   This means you can hear signals separated from the tuned frequency by multiples of the IF, i.e. 89.4, 100.1, 110.8, and 121.5 MHz if the front end of the receiver is broad band (cheap!) enough.   Since most commercial FM radios tune in odd decimal points (.1, .3, .5, .7, .9), 100.1 is the first available frequency that can be tuned. Hannu Ylioja, a Civilian Instructor with 2524 (Oakington) Squadron Air Training Corps in the United Kingdom, submitted a great deal of better and additional information on this topic.

You can DF a signal that is not audible!   Even when you can't hear the familiar ELT tone sweep, the ELT can be found!   Many ELTs are damaged in actual airplane accidents and that is one of the things that may happen to them.   All you need to do is compare the signal's deflection to the deflection on other frequencies (121.775 and/or 121.6 MHz).   If the deflection is the same on all three frequencies, it is probably noise and not a real signal.   If you don't receive deflection on those frequencies, you probably have a non-audible signal.  The Pointer 6000 practice beacon can be modified to transmit carrier-only to allow you to practice this.  See Practice Beacon Mods page.

If you are having trouble finding a null while body shielding, try wrapping a piece of cardboard in several layers of aluminum foil.   This will be a signal shield.   Continue to body shield the signal using your new "device."

You can also use a coffee can as a body shielding shield.   Although should we then call it simply "signal shielding?"   This has proved especially useful during a ramp search.   Body shielding may be just as effective, but there is at least the mental delusion that the coffee can works better.   It certainly will not find a distant signal, but its been used when the Tower called to complain about a signal on the airport.   The trick is actually a hand-me-down from Bill Burton, the Vice Wing Commander of Nebraska Wing.   He used it once when he was down here to find an EPIRB in a dock warehouse in Port Isabel.   The idea is that you point the open coffee can at the signal you hope to find.   You should tune the FM radio should be tuned all the way to the 108 end of the band.   ELT interference can work both ways--Ron describes a mission where the resident of the house didn't know the previous renter had left an ELT when he moved.   The Mom had knocked it off a shelf and they were suffering from interference on their TV.   When he described an ELT's sound and what it might look like, the son recognized that there was really one in the house.   This trick submitted by Ron Johnston of Brownsville, Texas.

If your L-Tronics LA-series aircraft DF isn't working, you can use a ground DF instead!  A future page is planned to detail the procedure.

One-way communication by DF.  If you can't communicate by radio to the ground team, transmit on 121.775 MHz (practice) or briefly on 121.5 MHz (actual).  If the ground team is listening to their DF unit, as they should, they can hear the aircrew's instructions and follow them.  You can regain communications or give critical instructions.

 

 

This page of the CAP Emergency Services Resources website was last updated 01/06/2009

1998 - 2007 Scott E. Lanis.  All Rights Reserved.