AE5PH 'Tenna Dipper

I really wanted an antenna analyzer, but the cost of even the least expensive units was too much for my budget. I decided to look at a homebrew solution. While there are a number of homebrew antenna analyzers on the Internet, each had one or more shortcomings. Some had performance issues, others required parts that had become difficult to obtain, and many were tricky to calibrate once constructed. I decided to build something simple, just to have some minimal means of tuning antennas in the HF bands.

What caught my attention was the 'Tenna Dipper, developed by Steve "Melt Solder" Weber, KD1JV. Rather than using a meter to indicate SWR, the 'Tenna Dipper uses a light emitting diode (LED) to indicate when the impedance bridge has nulled. That is, when the LED has dimmed or extinguished, the impedance bridge is close to or matched to 50 ohms, respectively. This is a crude indicator, be it is effective when the goal is to only shown when a (close) match has been achieved.

The 'Tenna Dipper has evolved over the years, starting with his original, minimalist design, and yielded two commercial products. One version was once sold by the Four States QRP Group. The current commercial offering is sold by Hendricks QRP Kits. There used to be a Yahoo Group for support of the Hendricks product, but it disappeared with the reorganization of Yahoo Groups in 2013.

After looking at the different designs of the 'Tenna Dipper, I decided that I could easily homebrew one myself. I wanted to have a 'Tenna Dipper similar to the Hendirks version, but with improvements where practical. I did not want to use a frequency counter using an Atmel ATTINY2313, as I had no previsions for programming Atmel microcontrollers. I did have a Microchip PIC16F628 and I can program those chips. I decided to use a PIC-based frequency counter designed by Wolfang "Wolf" Buscher, DL4YHF. While the counter supports a programming mode, I elected to leave out the programming button, as my application had no need for supporting that feature. I also used a ten-turn, 50 Kohm pot to improve frequency selectivity.

I developed a printed circuit board using EagleCAD. Below are some pictures of the completed circuit board and the finished 'Tenna Dipper project.

The accuracy of the frequency counter is about +/-10 KHz. Using my Homebrew Buddipole as a test subject, I adjusted its whips over the 20-meter band and measured the frequencies of the LED "null points" using my 'Tenna Dipper. I also used an MFJ-269 to measure the frequencies of minimum SWR for the same antenna adjustments. The results compared well, given the accuracies of frequency measurement.

While testing has demonstrated that the 'Tenna Dipper works reasonably well on lower frequencies, I discovered that it became insensitive on the 12-meter and 10-meter bands. This appears to be related to the frequency performance of the FT37-43 toroid. It may be possible improve the situation by replacing the toroid.

I gave a presentation on my homebrew 'Tenna Dipper at the July 2013 Richardson Wireless Klub monthly meeting. An Adobe Acrobat (PDF) file of the presentation slides is available below. The presentation goes into more detail about the history of the 'Tenna Dipper and the implementation and testing of my version.