The March/April issue of QEX is coming soon, and it is full of theoretical and practical technical articles that you don't want to miss.

In this issue, Gary Steinbaugh, AF8L, introduces us to "A Cybernetic Sinusoidal Synthesizer." The initial part presents some interesting history and theory of feedback control. The system includes an oven-stabilized crystal-controlled oscillator, a PLL frequency synthesizer with a low phase noise sinusoidal output, a variable gain RF amplifier for automatic power level control and an RF power meter with a digital readout in dBm and an analog voltage output. Subsequent articles will describe these circuits in detail. Ron Skelton, W6WO, takes us "Exploring Near-End-Fed Wire Antennas" by modeling his design using EZNEC, and then building a 40 meter version to verify the modeled performance. Ken Grant, VE3FIT, describes "A Versatile Two-Tone Audio Generator for SSB Testing." This handy piece of test gear could be a valuable addition to your test bench.

Thomas Alldread, VA7TA, continues to describe his "NimbleSig III" dual output DDS RF generator. This circuit provides signals over a range from 100 kHz to 200 MHz, with 1 Hz resolution. In this part of the series we learn about the control software design, computer interface, MPU programming and initial testing. Rudy Severns, N6LF, presents more of his research in "Experimental Determination of Ground System Performance for HF Verticals." Part 3 compares the performance of antennas using ground-surface radials and those using elevated radials. If you use vertical antennas on HF, or have thought about using vertical antennas on HF, you will want to read all of the articles in this series. Roger Monroe, K7NTW, introduces the process of programming a microcontroller in "Some Assembly Required." As a practical application, he describes how he used a microcontroller in the design of a QSK amplifier keying interface for use between his Ten-Tec Omni IV+ radio and his Heath SB-220 amplifier.

Ray Mack, W5IFS, continues his software defined radio column. In this installment of "SDR: Simplified," Ray looks at signals in the time domain and the frequency domain, and introduces the concept of Fourier transforms. He also explains the Nyquist criterion for sampling signals in analog to digital conversions as well as the filtering requirements for digital to analog conversions. Mark Spencer, WA8SME, has been sending results of his further data collection based on his article, "SID: Study Cycle 24, Don't Just Use It" from the September/October 2008 issue of QEX. The "Tech Notes" column in this issue includes some graphs of Mark's data, as well as a re-designed SID receiver and interface. The "Reader's Page" includes photos of two different GPS-derived frequency standards. Readers are encouraged to submit photos of their projects, to show off their handiwork.

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QEX is edited by Larry Wolfgang, WR1B, and is published bimonthly. The subscription rate (6 issues) for ARRL members in the US is $24. For First Class US delivery, it's $37; in Canada and internationally by airmail it's $31. Nonmembers add $12 to these rates. Subscribe to QEX today.

Editor's Note: Due to production difficulties, the March/April issue of QEX will be arriving about two weeks later than normal. Readers should expect to see their copies in their mailboxes in mid March. We regret any inconvenience this may cause.