Studying the Tenna Dipper Deluxe

I saw an interesting new kit from Hendricks QRP Kits yesterday called the Tenna Dipper, (designed by KD1JV). It tells you the 50 ohm resonant frequency of an antenna. Basically, you scan the frequency from the Tenna Dipper until an LED goes out and the read the resonant frequency from the display.
What I thought was even cooler was learning how the kit worked. I’ve included the links I used for research below.

The schematic is available on the Hendricks site as a pdf.

The kit uses a Wheatstone Bridge to cause the LED to go out when the antenna resonates at 50 ohms. The bridge is the workhorse circuit that provides antenna match information. It’s actually fairly easy to understand, check out the explanation at:
Wikipedia Wheatstone Bridge article.

A voltage controlled oscillator, 74HC4046, is used to generate the square wave sent to the antenna.
74HC4046 datasheet [pdf]

A 74HC4017 decade counter is used as frequency counter to feed the kit’s frequency display.
74HC4017 datasheet [pdf]

The frequency display is driven by an Atmel ATTiny2313 microcontroller.
ATTiny2313 microcontroller datasheet [pdf]

NOTE: I’m not associated with Hendricks QRP kits, I just thought this was a cool design to learn about.

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