Signal Strength Detection: Pointing you to the Best Signal
Duncan Wisniewski and Santhosh Theunduna
As part of a Radio lab design project at Auburn my partner and I came up with a detection and pointing system for an AM radio antenna. We selected this project because we observed that the direction the antenna was facing could change our signal from clear to unintelligible. Our end goal was to create an antenna which could locate and turn to the strongest signal in a single button push. The first step we took was to assemble the full wave bridge rectifier seen in figure 1 below. We connected this to an analog micro-ammeter to get proof of concept that our plan would work. We then simulated the effects of the full wave bridge rectifier as seen in figures 1 and 2 to create a DC voltage at the end of our radio.​
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Figure 1: LTSpice simulation of the radio and rectifier
Figure 2: outputs from the radio and the rectifier
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The DC output from this rectifier was given to an Arduino which ran a motor connected to the bottom of the antenna as seen in the pin out diagram in figure 3. The Arduino used the code in listing 1 to rotate and sample signal strength in a loop. Each rotation produces a graph like the one in figure 4. In this particular graph the signal was blocked almost entirely at one point resulting in the large drop in signal strength.
Figure 3: Arduino Pinout Diagram
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Listing 1: Signal Strength Sampling
Figure 4: Signal Strength Graphed
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The next segment of code was used to rotate in the reverse direction back to the point where the strongest signal was read. This often was a function generator if one was on but in an area without FGens the antenna would usually select the window.
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Listing 2: Selecting the Best Signal
After combining all of these elements into a final product we successfully created a signal strength detector and antenna pointer seen in Figure 5 below. This video features the antenna rotating and successfully finding the function generator behind it three times in a row.
Figure 5: Demonstration
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The Detector worked most of the time as a signal strength detector, but variations in audio volume could cause issues. This system worked very well as a signal detector in an insulated room where the radio station was only receivable at one point in the rotation. You can try this project yourself using the code found on GitHub