The July/August issue of QEX is coming soon, and it is full of theoretical and practical technical articles that you won't want to miss. QEX is the ARRL’s “Forum for Communications Experimenters.” Published bimonthly, it features technical articles, columns and other items of interest to radio amateurs and communications professionals. The mission of QEX is threefold: To provide a medium for the exchange of ideas and information among Amateur Radio experimenters; to document advanced technical work in the Amateur Radio field, and to support efforts to advance the state of the Amateur Radio art.

Craig Johnson, AA0ZZ, presents a “Programmable PLL Local Oscillator for HF Receivers, Transmitters and Transceivers.” Johnson chose the Silicon Labs Si570 DSPLL programmable PLL synthesizer IC and custom software to build a local oscillator that produces a stable 10 to 157 MHz output signal. The oscillator can provide the local oscillator signals for quadrature sampling detector receivers and quadrature sampling encoder transmitters on the 80-10 meter amateur bands.

James Hontoria, W1JGH, describes “A 10 MHz to 6 GHz Power Meter.” Based on a Mini-Circuits ZX47 power detector, this meter uses an LCD to give a direct readout of power levels from –55 dBm to +10 dBm. Gary Appel, WA0TFB, describes software he wrote for “Filter Synthesis Using Equal Ripple Optimization” techniques. As he explains, the Newton-Raphson method is a way to use an initial approximation and then to arrive at a better approximation of the value. In this case the goal is a filter design with equal ripple across the passband.

Robert Zimmerman, NP4B/VE3RKZ, describes five years of research at McMaster University in “Transmission and Reception of Longitudinally-Polarized Momentum Waves.” James Clerk Maxwell’s famous equations of electromagnetic radiation predict an alternative form of radiation, which Zimmerman refers to as vector potential radiation. He was involved in research that results in a demonstration of the communications potential of what was previously considered to be only a theoretical curiosity. David Gordon-Smith, G3UUR, presents a filter design article in “Extended Bandwidth Crystal Ladder Filters With Almost Symmetrical Responses.” Gordon-Smith uses inductors in parallel with the crystals to build hybrid ladder filters and restore symmetry to the filter response.

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