Exploring RF - Conducted By David Newkirk, WJ1Z Senior...

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Now that ARRL Radio Designer is on the street, we’re hoping that ham interest in exploring radio-frequency (RF) technology through computer-based modeling will take off in a way that hasn’t been possible before. This column is part of taking that show on the road—a place for suggesting ARRL Radio Designer applications we hope will be interesting to many hams. But this column won’t stop there. Many useful electronic and RF circuit design programs have been with us for years in various forms, and new ones keep appearing. For starters, I’m thinking of the various commercial products based on the University of Cali- fornia at Berkeley’s SPICE (Simulation Program with Integrated Circuit Emphasis)—at least one of which, MicroSim Corp’s PSpice , is available free in a limited-function evaluation version, and other of which, MICRO-CAP , is available jointly from Addison-Wesley Publishing and Benjamin/Cummings Publishing in a low-cost student edition. Just sketching the abilities of the many SPICE derivatives would take several pages. A diskful of antenna, transmission-line and propagation software now ships with every new ARRL Antenna Book sold, and software is also available with The ARRL UHF/Microwave Experimenter’s Manual —what can those programs do? And what about the freeware and shareware that’s almost everywhere? There’s a lot to be excited about if you’re interested in using computer-aided de- sign (CAD) and computer-aided engineering (CAE) in Amateur Radio, and QST will share that excitement through Exploring RF. Optimizing Circuit Performance with ARRL Radio Designer One of the ARRL Radio Designer features we’re most excited about is the program’s ability to optimize circuits—to make cir- cuits work better, or to modify circuit performance according to specified goals. I suggested in October QST ’s ARRL Radio Designer article 1 that one use for this feature might be to tweak a 2-meter receiver preamp for a better noise figure, but that’s a pretty far-out example for many of us. Then I went on to describe an antenna-tuner optimization that’s a very nice example of optimiz- ing a circuit almost, but not exactly, like the one actually shown. 2 Elsewhere in this issue, Andy Griffith’s “Getting the Most Out of Your T -Network Antenna Tuner” includes some eye-opening findings on just how lossy a T network can be when transforming some impedances to 50 . ARRL Radio Designer , manipulated by yours truly, backed up Andy’s findings and even provided a few graphics. Here’s how I did it—and how you can use ARRL Radio Designer ’s optimizer to simulate adjustable T networks, too. Exploring RF Conducted By David Newkirk, WJ1Z Senior Assistant Technical Editor e-mail: dnewkirk@arrl.org The T Network in Schematic and Netlist Form Figure 1 shows Andy’s T net’s schematic with a few additions and changes. Here’s the corresponding ARD netlist block: BLK CAP 1 2 C=?20PF 82.1733PF 1000PF? Q=1000 ; C/IN\ IND 2 0 L=?0.1UH 30.2528UH 35UH? Q1=200 F=2.52MHZ;L
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Exploring RF - Conducted By David Newkirk, WJ1Z Senior...

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