HANDI-Finder Information

d) --Off-Axis Nulling or No Null at all: With a known strong signal, if there is constant off-axis nulling or no null at all, check the continuity from the antenna wire to a circuit point on the board foil using an Ohmmeter. Flat washers are manufactured by stamping, and thus have a slight "cup" cross-section. Put the rounded side against the board foil. It was discovered that with the concave side against the board pad, it is often very difficult to tighten the hardware enough to compress the center of the washer so that it reliably contacts the board foil, which is sitting in a bit of a depression caused by the surrounding "solder mask" coating. Latest preferred method: Put the screw through from the component side, then on the non-component side, the washer with rounded side against the board foil pad, then the antenna eyelet, then the lockwasher, then the nut, and tighten. The HANDI-Finder® is a HANdheld DIrection Finder which can be used to localize both AM and FM carrier-based sources using a single connection to the antenna input of an FM receiver tuned to the frequency of interest in the range of 45 to 450 MHz. It has been designed for bare-bone functionality as well as low power consumption, simplicity, and economy! Because it is both an easy-to-build kit for the beginner and a convenient basis for further experimentation by those with more experience, it makes a great club project! Overall, it is a quick, inexpensive way to implement the concept of direction finding, and provides something relatively compact to keep readily available for locating sources of interference. Except for adding a handle, fabrication is minimal. Two open-loop antennas (not supplied) are made from coat hanger wire bent into halves of a "bow-tie" shape and mounted directly to the circuit board, as illustrated in the "layout" drawing. The 50-Ohm coax downlead (not supplied) is connected to an FM receiver and detects the carrier regardless of whether the transmission mode is AM or FM. The unit is switched on (UP) and rotated ...