Welcome to the N1IR Electronics Website. Totally off the cuff, one take, unrehearsed video projects for anyone interested in amateur radio, electronic design, makers, hardware hackers and science.

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Training the hand and mind since 1982.

Sunday, April 3, 2011

Video #6 TDA, RDF, WTF?

Hi I'm back, after being ill for a couple of weeks. Shout out to C Morgan my first follower.

Today we have my video on TDA Time Difference of Arrival Radio direction finding. A basic ciruit to turn your HT into a killer Fox hunting / ELT hunting piece of equipment. All you need is a few coat hangers, some coax, couple of diodes, resistors and caps and an audio square wave oscillator of your choice. There is an addition to the video I forgot to mention the inductor choke in the circuit, it to prevent R.F. getting into the audio oscillator circuit.

How it works:
Time Difference of Arrival RDF (DF) sets work by switching your receiver between two antennas at a rapid rate. When both antennas are the same distance from the transmitter, the RF phase received by both antennas will be identical, with the same impedance in both diodes. If the two antennas are different distances from the transmitter the RF will have a different phase at each antenna and one diode will conduct more than the other, like an analog OR gate. If we switch between the antennas 500-1000 times a second, this phase change will be detected by an FM receiver as a 500-1000 Hz tone. By turning the antennas for a null in the tone, your two antennas will be perpendicular to the transmitter. Additionally when a diode is conducting via switch and battery in forward biased mode the circuit operates in Yagi (Rec) mode and you can determine what general direction the signal is coming from. Eliminating the confusion between a front or rear signal of receiver signal that you would get in (DF) mode

Video 6 Part two, I go over what an ELT is and some basic RDF tricks.