****************************************************************** * ARD9410.TXT -- Ver 1.0, February 21, 1995 * * * * This file is most readable when viewed in a fixed-pitch * * type font, such as Courier or New Courier. * * * * Source: The American Radio Relay League (ARRL) * * 225 Main St * * Newington, CT 06111 * * USA * * tel 203-594-0200 * * e-mail: hq@arrl.org * * * * Subject: Overview of the features and capabilities of ARRL's * * radio-frequency (RF) computer-aided-design (CAD) software, * * ARRL Radio Designer. * ****************************************************************** For more information about ARRL Radio Designer, address an e-mail message to ARRL's automated Internet information server: info@arrl.org including as your message's sole text the four lines SEND ARD.TXT HELP INDEX QUIT You need not specify a subject unless your mailer requires it. The HELP line nets you the info server Help file; the INDEX line nets you the latest listing of all information files on the server. You can also download the latest ARD.TXT from the ARRL BBS at 203-594-0306. ****************************************************************** This article appeared on pages 21-26 of October 1994 QST(R) magazine, is copyright 1994 by the American Radio Relay League Inc, and is provided herein solely for the personal use of the recipient. (QST[R] is published monthly by the American Radio Relay League (ARRL), a membership organization of, by and for radio amateurs.) In the text to follow, \ / delimiters indicate \superscript/; / \ delimiters indicate /subscript\; and ** delimiters indicate *italic* type. ****************************************************************** Introducing ARRL Radio Designer: New Software for RF Circuit Simulation and Analysis If you've done any hobby computer-aided design at all, you've probably used CAD mainly for designing and enhancing your antenna system. Now you can put your PC to work modeling radio circuitry at the *station* end of your feed line! By David Newkirk, WJ1Z Senior Assistant Technical Editor A glance into just about any current Amateur Radio magazine or club bulletin confirms that computerized antenna modeling now qualifies as a standard ham activity. With program names like NEC, MiniNEC, MN, ELNEC and ARRL MicroSmith well-established as household words--in ham households, at least--we don't even blink when someone gloats over another computer-optimized Yagi or gulps when modeling unmasks a new skywire as more of a worm warmer than an ether buster. What, then, keeps so many of us from modeling radio *circuits* with our computers--designing, simulating and analyzing the innards of the "gray boxes" we connect to the antenna systems model with such enthusiasm? Availability, for starters. If versatile, affordable RF CAD software exists, how do we find it? Even the worthiest of the uncountable neat little (and not so little) utilities written by hams to solve or simulate or design particular radio-electronics problems or circuits rarely makes headlines.\Note1/ ******** \Note1/Did you catch Dean Straw's "So What's New in The ARRL Antenna Book?" (the lead article in last month's QST) or checked out the companion software available for The ARRL UHF/Microwave Experimenter's Manual? ******** Program suitability to the task of realistic RF modeling is perhaps the biggest hurdle. General-purpose simulators like *PSpice*(TM) and *MicroCAP*(TM) are well-established in college- level EE programs. They are offered as low-cost, general-purpose simulators, but the accuracy of their available active-device model libraries, especially in the important areas of noise (noise-correlation matrix calculations) and distributed parasitic reactances so important in RF modeling, significantly limits their usefulness above 100 MHz. What's more, these programs don't "speak RF"--they're not equipped to directly report circuit performance in RF-standard terms like S (scattering), Y (admittance), impedance (Z) and other network parameters. Now there's a new choice. Working in association with Compact Software of Paterson, New Jersey, ARRL is proud to unveil ARRL Radio Designer 1.0--realistic, affordable (price class, $150) RF CAD Windows(TM) software for radio amateurs!\Note2/ ******** \Note2/ARRL Radio Designer is available from Publication Sales at ARRL HQ for $150, plus $5 shipping/handling (UPS delivery). You can order by phone (203-594-0200) or use the order form in the ARRL Publications Catalog elsewhere in any issue of QST (the order number is 4882). ARRL Radio Designer software and example files are shipped on two high-density 3-1/2-inch IBM compatible diskettes. The instruction manual includes tutorial and reference information. See the article text for computer hardware requirements. ******** What is ARRL Radio Designer? ARRL Radio Designer, a derivative of Super-Compact(R), Compact Software's industry-standard linear circuit simulator, analyzes the performance of linear, small-signal active and passive dc, AF and RF circuitry, including amplifiers, filters, matching networks and power splitters and combiners. ARRL Radio Designer tools include * Analysis (prediction of circuit performance); Optimization (automatic adjustment of circuit performance to meet goals you specify); * Voltage Probe (predicts the signal level at any point in a simulated circuit); * Statistical Analysis (simulates the effect of component value variations [such as those attributable to tolerance or temperature coefficient] on circuit performance using Monte Carlo techniques); * Time Domain Analysis (simulates circuit performance in response to a steady-state time-domain signal using impulse, step, pulsed carrier or user-defined stimuli); * Manual matching-network synthesis via Circles, an interactive Smith Chart utility; and * Databanks (device-manufacturer-supplied S-parameter and noise data you can incorporate in your circuit simulations). ARRL Radio Designer reports the results of its simulations in graphical (rectangular and polar) and tabular form, onscreen and via any Windows (TM)-compatible printer, in terms of * S, Y, Z, group delay and voltage probe parameters for n-port networks; * Chain (ABCD), hybrid (H), inverse hybrid (G), gain, voltage gain, and stability parameters for two-port networks; * magnitude of reflection coefficient, phase of reflection coefficient, VSWR and return loss parameters for one-port networks; * gain, gain matching and noise parameters; and * complex S, Y, Z, H, G, chain (A), gain matching, noise matching and voltage probe parameters. Installing and running ARRL Radio Designer requires, at minimum: a 386, 486 or Pentium IBM PC or 100% compatible (math coprocessor not required, but strongly recommended); 8 Mbytes of RAM;\Note 3/ ******** \Note 3/For those who must ask: ARRL Radio Designer has been successfully installed and used on a coprocessorless 386SX-16 with 4 MB of RAM running in 386 enhanced mode. This required critical management of Windows resources, ARRL Radio Designer ran quite slowly because of the system's slow clock speed, 386 CPU (generally, 386s take two clock cycles to do what a 486 does in one) and lack of a coprocessor. ******** * a 3.5-inch, high-density floppy drive; a hard disk with at least 5 MB of free space; * Microsoft Windows (TM) 3.1 or higher; and * a mouse or equivalent pointing device. So much for the fact dump. You've got to see ARRL Radio Designer in action to appreciate it, so let's put it work! ARRL Radio Designer in Action We'll use the circuit shown in Figure 1--the post-mixer amplifier from Hayward and Lawson's Progressive Communications receiver (November 1981 QST)--as our first test case. Reduced to its essentials, the process involves just four steps: 1. Mark each of the circuit's *nodes*--points of interconnections between its components or *elements* (Table 1 lists ARRL Radio Designer's entire set) with an exclusive number between 0 and 999 (Figure 1); 2. Type the circuit's elements and node numbers into a *netlist* using ARRL Radio Designer's Circuit Editor (Figure 2); 3. Press ARRL Radio Designer's Analyze button; and 4. Graph, table, save and/or print the results to your heart's content (Figures 3, 4 and 5). A 6-dB attenuator follows this post-mixer stage in the Hayward/Lawson receiver. With it in line, they reported the amplifier's gain as "about 16 dB." Subtracting 6 dB from the MS/21\ trace in Figure 4 or Figure 5 reveals that our model's HF/VHF gain agrees quite closely with the findings of Hayward and Lawson. Circuit Tuning How does a double-tuned-circuit filter's response shift as you tune it with a two-section capacitor? Sure, you can *hear* the peak sweep by if the filter's in your receiver, but what does that effect *look* like? If you happen to own a spectrum analyzer and tracking generator, you can demonstrate it easily enough. Or you can let ARRL Radio Designer's Tune feature show you (Figure 6). Statistical Analysis, Monte Carlo Style Real components vary in value with temperature and tolerance. Using ARRL Radio Designer's statistical analysis feature, you can determine the effect of these variations on circuit performance, as I did for the op-amp audio filter described by Henry J. Perras, K1ZDI, in March 1994 Hints and Kinks. Figure 7 reports the happy news that 1000 out of 1000 K1ZDI filters built with 5%- tolerance capacitors and 1%-tolerance resistors should work acceptably well with *no post-construction tweaking whatsoever*, and Figure 8 shows how those 1000 filters' 2-kHz losses vary around the nominal value of –2.52 dB as result of component tolerances. Putting Optimization on the Case It's one thing to use "cut and try" techniques to nail down one variable component value in a circuit when you've got all the others under control, but you can just about kiss a weekend's worth of experimenting goodbye if you need to vary more than one. If the optimization job you want to do requires esoteric test equipment--say, a noise figure meter--or presents a "solution surface" so complex that one-dimensional tweak-and-measure investigation is doomed from the start, you and ARRL Radio Designer's Optimization engine stand to become fast friends. Figure 9 shows a simple example of such a challenge--an antenna matcher with one variable inductor and one variable capacitor. Your job: Find the L and C values that let that tuner turn a highly reactive antenna load (16 - j2256 ohms at 1.83 MHz) into 50 ohms, resistive. Your choice: Put ARRL Radio Designer on the case (Figure 10). Your reward: a match (Figure 11). Let the Fun and Learning Begin! That's all the space we can devote this month to QST's first look at ARRL Radio Designer. What happens next? For starters, you can expect to see more about ARRL Radio Designer in future QSTs-- whenever we can appropriately use it to confirm or improve a circuit design, or to illustrate a point, for instance. Our overriding hope, though, is that you will put ARRL Radio Designer to work, and share your experiences and findings with us and your fellow hams. The way we see it, it's only a matter of time before RF-accurate CAD becomes every bit as routine to radio amateurs as simulating an antenna with MiniNEC or cruising through a contest with CT or NA. We're pleased to offer ARRL Radio Designer as a doorway into that new phase of ham radio's growing computer tradition. [sidebar] Circuit Analysis, Circuit Synthesis--What's the Difference? ARRL Radio Designer concentrates on circuit analysis as opposed to circuit synthesis, but what does that mean? With a circuit synthesis program, you define a problem ("Build me a fifth-order Chebyshev low-pass filter with 50-ohm terminations, 0.1 dB of ripple and a 3-dB corner frequency of 230 MHz") and the program responds with appropriate component values. Circuit analysis capability, if present, is usually limited to relatively simple simulations of the program's own solutions. A circuit analysis program, on the other hand, predicts the performance of your solutions. You enter your circuit into the program in coded form (commonly, as in ARRL Radio Designer, this is a text file called a netlist, short for network list) and provide guidance for the program's simulation engine ("Calculate this circuit's behavior at 500 exponentially stepped frequencies from 100 kHz from to 100 MHz, and graph the real and imaginary components of its input impedance with its output terminals loaded by 1.5 kilohms in parallel with 3 pF"). The appearance, accuracy and quality of the results you get depend on how completely you specify (and how completely you the program lets you specify) your circuit's component characteristics and terminations, the accuracy of the program's mathematical component models, and the program's reporting capabilities. ARRL Radio Designer goes far beyond plain-vanilla analysis, however. Its Circles utility can help you synthesize matching network values, Smith Chart style. You can command its Tune function to step selected components' values through sequences or ranges of values as you watch the results onscreen. You can predict the effect of component tolerances on circuit performance using Statistical Analysis. Even more excitingly, you can put ARRL Radio Designer's Optimizer to work tweaking your circuit for peak performance--hand it your best cut at a low-noise 2-meter preamp, say, and walk away with a design that's a dB or two quieter. True to its name, ARRL Radio Designer doesn't do "just synthesis"--it helps you design radios.--WJ1Z [sidebar] ARRL Radio Designer Versus Professional Simulators Even circuit-simulation software costing tens of thousands of dollars or more--as the best such programs do--can't accurately model absolutely every circuit function in, say, a shortwave ham transceiver. Since even the best simulators can't do everything, what subset of "less than everything" can ARRL Radio Designer do? To put it another way, what do professional-grade simulators got that we ain't got? The answer has three parts: schematic capture, microwave/optical capability, and nonlinear simulation. Schematic Capture Schematic capture, standard with some high-end circuit simulators and optional in others, lets you draw a schematic onscreen and generate a netlist--the circuit's text equivalent in a form digestible by the simulator--from the drawing. Super-Compact, ARRL Radio Designer's big brother, doesn't include schematic capture (Compact's Serenade schematic editor is available as an option); its text-based netlist interface was designed for compatibility across platforms with widely variable graphics capabilities. ARRL Radio Designer therefore doesn't include schematic capture. For sprawling digital circuits, schematic capture, though tedious, is almost a necessity. For RF applications and simple circuits, however, manual entry is significantly faster and easier. Microwave/Optical Capability The lion's share of today's commercial and military radio R & D bucks flows into UHF/microwave and fiber-optics projects. At those frequencies, tuned circuits rarely consist of "lumped" inductances and capacitances--a tuned circuit consisting of 0.0001 pF in parallel with 0.0001 mH resonates at about 1592 GHz, but I dare you to actually build one!--so stripline, microstrip and other transmission-line and waveguidelike structures do the job instead. Professional-grade circuit simulators can model these structures using actual physical dimensions and the real characteristics of their conductors, dielectrics and substrates. In contrast to this, ARRL Radio Designer models tuned circuits in terms of lumped L and C. Its practical applicability therefore declines wherever radio physics dictates that you must switch from LC circuits to stripline, microstrip, YIGs, dielectric resonators or waveguides--typically above 1 GHz. Small- Versus Large-Signal Analysis Oscillators stabilize their amplitudes; mixers mix; modulators modulate; amplifiers distort; rectifiers rectify; frequency multipliers multiply; and AGCed stages "AGC" because amplitude- nonlinear device behavior. Because ARRL Radio Designer is a linear, small-signal simulator, it cannot simulate these large- signal effects. To get a handle on this, check out the bipolar junction transistor amplifier in Figure 1. That drawing includes no power supply connections--because the ARRL Radio Designer model doesn't need them! You can successfully analyze the circuit's performance, and plot its gain and frequency response, without connecting its bipolar junction transistor to V/CC\. How can this be? This can be because the Figure 1 circuit is a linear amplifier, and ARRL Radio Designer is a small-signal, linear simulator. When, working at your radio bench, you power a real transistor at a particular voltage and bias it just so, you also set its supply- and bias-dependent parameters (starting with a bipolar junction transistors alpha or a FET's transconductance) to particular values. Modeling in ARRL Radio Designer, you specify your devices' parameters according to the power-supply and bias levels you expect to exist in the modeled circuit, and ARRL Radio Designer then reports your circuit's performance with devices exhibiting those parameters. The distinction between small-signal and large-signal analysis pretty much boils down to this: A device operates in its small- signal region when its "operating" or "bias point" (which its power-supply and bias levels determine) doesn't shift in response to its input signal. Driving the device with a signal large enough to shift its bias point results in nonlinear, dynamically variable performance that the "hardwired" device parameters of a linear simulator's netlist don't reflect. ARRL Radio Designer therefore can't model nonlinear effects like frequency translation, intermodulation, AGC, and the results of subjecting good devices, or well-modeled designs, to absurd or greatly divergent bias, drive or power-supply levels. If, for instance, you want to see what happens when you power a 13.8-V amplifier design at 6 V, you can model its gain under the new conditions. Working carefully, you can even simulate the frequency- and phase-response shifts that may occur as a transistor's internal capacitances change in response to different terminal voltages and currents. But you won't be able to tell if your underpowered amplifier is any more or less linear because ARRL Radio Designer's active devices are crunchproof and distortion-free by definition! Nonlinear Analysis Professional-grade nonlinear simulators, including Compact's Microwave SCOPE and Microwave Harmonica, can do most types of nonlinear AF and RF simulation extremely well--beginning at roughly the cost of a new car. PSpice, largely intended for dc, digital and audio design, and available (in a limited-capability evaluation version) as freeware from computer bulletin boards, can usefully simulate some nonlinear effects--if you don't need accurate results at VHF/UHF frequencies. So where does that leave linear, small-signal ARRL Radio Designer? In good company, as it turns out. Compact Software gurus tell us that perhaps 90% of all professional microwave and RF circuit simulators sold are linear. Even though we stand on the threshold of the DSP age, our radios still consist largely of linear circuits. Because linear AF and RF design techniques will remain important in professional and Amateur Radio for the foreseeable future, an affordable RF-circuit simulator stands to be of significant use to hams interested in getting current and keeping current with modern RF techniques. That's why we're pleased and excited to bring ARRL Radio Designer to you.--WJ1Z Table 1 [page 23] ARRL Radio Designer Circuit Elements Passive Lumped Elements CAP Capacitor models DIOD Diode models DLY Time delay IND Inductor models MUI Coupled inductor models PLC Parallel connection of inductor and capacitor PRL Parallel connection of resistor and inductor PRC Parallel connection of resistor and capacitor PRX Parallel combination of resistor, inductor and capacitor RES Resistor models SHO Short circuit SLC Series connection of inductor and capacitor SRL Series connection of resistor and inductor SRC Series connection of resistor and capacitor SRX Series connection of resistor, inductor and capacitor TRF Transformer models (ideal two- and three-winding types) Black-Box Elements IMP Two-terminal impedance ONE Two-terminal element specified by admittance, impedance or reflection coefficient TWO Three-terminal two-port specified by admittance, impedance or S parameters Distributed Elements CAB Coaxial cable models TRL Transmission-line models Controlled Source and Active Elements CCG Current-controlled current source CVG Current-controlled voltage source BIP Bipolar transistor model FET Field-effect transistor model OPA Operational amplifier VCG Voltage-controlled current source VVG Voltage-controlled voltage source Figure 1--We'll simulate the post-mixer amplifier from the classic Progressive Communications Receiver described in November 1981 QST by Wes Hayward, W7ZOI, and John Lawson, K5IRK. The first step in readying this circuit for ARRL Radio Designer analysis merely involves marking its nodes--its points of component interconnection--with numbers, 0 being the default for circuit common (I circle mine to distinguish them from device pinouts, wire designators, and so on). How come no power supply connections? The "ARRL Radio Designer Versus Professional Simulators" sidebar tells why. Figure 2--Next, we use ARRL Radio Designer's Circuit Editor--just an ASCII word processor--to specify each of the amplifier's components in network list--netlist--form: FT:1.4E9 ; Hz (1.4 X 10\9/ Hz is 1.4 GHz) Ic:30 ; mA Rd:(26/Ic) B:49 BLK CAP 1 2 C=0.01UF RES 2 0 R=470 RES 2 3 R=1000 BIP 2 4 5 A=(B/(B+1)) RE=RD CE=(1/(FT*2*PI*RD)) RB1=7.5 MUI 4 3 3 0 L1=46UH L2=46UH K=.999 CAP 3 7 C=0.01UF RES 5 0 R=56 CAP 5 6 C=0.01UF RES 6 0 R=5.6 BJTAMP:2POR 1 7 END FREQ ESTP 1MHZ 200MHZ 100 END Highlights in this particular netlist: * The four lines after the file header contain data for use by the circuit's transistor model. They are FT (f/T\, current gain- bandwidth product), Ic (I/c\, collector current), Rd (r/d\, diffusion resistance) and B (beta, current amplification factor). * BLK marks the beginning of a netlist block. * The BIP line specifies a bipolar transistor intended to simulate a 2N5109 running at 30 mA of collector current, using equations to derive the transistor's alpha (A) from beta (B/(B+1)) and emitter capacitance (CE) from f/T\ and r/d\ (1/(FT*2*PI*RD)). The model's emitter resistance (RE) is set equal to R/d\. * The MUI line specifies mutually coupled 46-uH inductors with a coupling coefficient of 0.999 (the number 9s in effect sets the number of decades of frequency range); * The BJTAMP:2POR 1 7 line names the circuit BJTAMP and defines it as a two-port network with terminals at nodes 1 and 7; and * The FREQuency block tells ARRL Radio Designer to simulate BJTAMP's performance at 100 exponentially stepped frequencies from 1 to 200 MHz. Our netlist completed, we click on ARRL Radio Designer's Analyze button and go! Figure 3--The analysis done, we pop ARRL Radio Designer's Linear Reports dialog to specify the simulated performance parameters we want to see (the S parameters MS/21\ [magnitude of forward gain], MS/11\ [magnitude of input reflection] and MS/22\ [magnitude of output reflection], and NF [noise figure], and how we want them displayed. Figure 4--How ARRL Radio Designer delivers the goods onscreen. You can control the appearance of everything you see in an ARRL Radio Designer report--colors, fonts, titles, graph scaling, the works. Figure 5--Need hard copy? Here's how the Figure 4 report rolls out of a laser printer in portrait orientation. ARRL Radio Designer's gives you wide control over its printer output, including line weights, fonts and color. (We don't have a color printer, so I set all of the report traces' colors to black for this version.) Figure 6--Here's what happens when ARRL Radio Designer's Tune feature steps a double-tuned-circuit filter's two-section tuning capacitor through part of its range in 5-pF increments. The filter simulated (a bottom-coupled 80-meter design from Solid State Design for the Radio Amateur) uses a small inductor for coupling. The coupling inductor's reactance, and therefore the coupling between the filter's resonators, increases with frequency, and you can see the effect of this as a barely perceptible insertion-loss decrease as the filter sweeps from 3.5 to 4.0 MHz. When you activate Tune, ARRL Radio Designer switches into Accumulate mode to let you see up to 20 simulations at once. Figure 7--You can use ARRL Radio Designer's Statistics feature to explore the effects of component tolerances on circuit behavior. In this analysis, ARRL Radio Designer evaluated 1000 iterations of an audio filter design while varying its frequency-critical component values within specified tolerances, pass/fail-testing each trial on the basis of loss at 2 kHz. The target loss range was 0 to -5.52 dB. Figure 8--Clicking on Histogram charts how the filter's 2-kHz loss varies around the nominal value of -2.52 dB across a population of 1000. Figure 9--Ulrich L. Rohde, KA2WEU, described this antenna matching network in November 1992 QST's "Recent Advances in Shortwave Receiver Design." Finding the L and C values that let this network match a particular load--assuming that that the load is within the network's matching range--is a piece of cake for ARRL Radio Designer's Optimizer. Figure 10--ARRL Radio Designer's Optimization engine lets you use random and gradient techniques to zero in on complex circuit solutions you couldn't hope to achieve by cut and try. This screen dump catches ARRL Radio Designer in the act of adjusting the Figure 9 network to match a 16 - j2256 ohm load to 50 ohms at 1.83 MHz. (In practice, turning off the Optimizer's display feature greatly speeds a solution because the computer doesn't have to stop to calculate and redraw the graphs each time it tries new values.) The optimization goal: simultaneous achievement of tuner-input Z parameters of RZ/11\=50 (real part of impedance, 50 ohms) and IZ/11\=0 (imaginary--reactive--part of impedance, 0 ohms)--"50 ohms, resistive." Figure 11--We have a match! (About 1800 iterations later, ARRL Radio Designer had fought the error function down to a number on the order of 10E-5, so I declared the job done.) Now compare these traces' 1.83-MHz values with the optimization goal I stated in the Figure 10 caption.