Of Free Software
Back when personal computers were new to the world and Basic was the common man's programming language of necessity, there were hundreds of new little applets that kept popping up to solve specific calculation tasks. It was great sport, as well as a display of mental cunning, to develop such programs and then figure out a way to make them available to the public. Remember that at the time (early to mid 1980s) a TRS-80 or a Commodore 64 would set you back a couple hundred dollars, and the Internet was just a gleam in Al Gore's eye.
Eventually, new languages like Pascal, Fortran, and some really strange language known as simply "C" arrived for MS DOS, and even for Apple DOS. I personally latched onto Pascal simply because in the late 1980s when I was at the University of Vermont working on my EE degree, that was the language du jour. Our microprocessor lab consisted of an Intel 8088 proto board for machine language practice. One of our first Pascal programming exercises was to create a routine that would convert a base-10 number to a Roman numeral (not as straight-forward as you might think once you get above 48 - try converter). There was no such thing as an Integrated Development Environment (IDE) or visual development tools. Performing a divide-by-zero operation caused the entire computer to hang (however, rebooting took about 30 seconds due to the small OS size, with no anti virus software to load, maybe a printer driver, etc.). I was immediately smitten by the programming bug (no pun intended) and set about to write routines for every application I could - or might - use in my daily engineering chores.
Eventually, spreadsheet files with calculation functions began getting posted on bulletin boards along with the applets, but many people did not have access to spreadsheets because they were part of rather expensive office packages. A lot of the computers did not have the amount of memory required to load the spreadsheets, and even worse yet, the vast majority of users did not know how to dial into or use a bulletin board service. Even EasyCalc pushed the memory limits of early PCs. That put file sharing - programs and spreadsheets - out of the realm for all but the most technically savvy. Many people procured their non-commercially distributed software on 5-1/4" floppy disks either via the mail (ordering from computing magazines) or via the Sneakernet. Those were rough days to be a programming enthusiast.
Stored on a CD in my safe is a collection of many of those old DOS routines that I used regularly. A few years ago I transferred everything from 3-1/2" floppies onto CD. The downside of that is that due to migration in the plastic, most of that data will over time become too corrupted for even error correction to handle, so it will be lost forever. The upside (kind-of) is that by then, the 64-bit architectures of new PCs will not even emulate 16-bit DOS to run them. As recently as sometime around 2000-2001, I was still using a DOS program for designing transistor biasing circuits that plotted gain, noise, and stability circles. Only fairly recently did I replace a DOS-based Smith Chart program with a Windows version. Does anyone else out there remember using the ground-breaking Cascade program by Amplifonix (ported to Windows and improved by Spectrum Microwave), or HP's AppCAD (also ported to Windows and improved)? There was a program that Microwave Journal mailed out to subscribers in the early 1990s, but I cannot recall its name; does anyone remember the name?
Most of the popular old programs can still be located with a search engine, and there are many, many websites with extensive lists of links to other websites that host the programs. Of course, RF Cafe also maintains a list of its own - check out the Calculators and Software pages to see what I have. Since it would likely be considered a copyright violation to actually store and offer them for download on RF Cafe, there are links to other sites that either legally or illegally host the files. The RF Globalnet website has a huge collection of software that has been uploaded, supposedly, only by copyright holders, so that is another good source. You will find that most sites are replicas with a large percentage of dead links - especially for the DOS apps.
Throughout the years, hobbyists and professionals alike have continued the task of creating very useful programs and applets that have made the lives of fellow hobbyists and professionals much easier. Of course, the newer ones are written to run either in Windows or Linux (some MacOS), and there is a whole host of online apps that run in your Internet browser. One of the drawbacks of using the free programs is that they do not provide for saving configuration files so that you do not need to start over again every time you run the application. There is an advantage in looking for calculators and simulators based in a spreadsheet in that the spreadsheet program itself provides the ability to save your final configuration.
You do need to be aware of the fact that there are a lot of erroneous results produced by these programs. It is amazing to me that even the most expensive commercial applications get away with placing the onus of results on the user with a simple disclaimer statement to the effect of, "It is the responsibility of the user to verify that results meet the expectations, and shall not hold <company name> liable for any damages due to incorrect results." I do not recall having ever heard of a case where someone successfully sued over bad data produced from engineering software - do you?
RF Workbench, originally marketed commercially as "TxRx Designer," was and still is my only major foray into the formal engineering software world. When it debuted sometime around 1992-1993, RF Workbench was quite advanced insofar as features. I wrote every line of code from scratch for the moveable windows, drop-down menus, mouse driver, 2-D and 3-D graphical outputs, and even the printer driver. Extensive error trapping was coded in to prevent any possibility of the user entering data that would cause the system to hang or crash. Once the world went Windows, I changed the name to its current incarnation as RF Workbench, and began offering it as Shareware. The program has been included on countless disks and CD collections of engineering software. If you go to RF Globalnet, where I uploaded the program to their servers way back in 2000, you will see the following notice: "RF Workbench is the most frequently downloaded software on the site." Although I cannot prove it, I suspect it might be the most-used RF system design tool ever. Maybe the price of $0 has had something to do with the phenomenon.
Another item that I have made available free of charge from RF Cafe is the RF Cafe Calculator Workbook. It is an Excel spreadsheet that is chock full of useful calculators that electrical engineers will appreciate. Some of the more advanced programming features of Excel are employed to make the interface a little more user friendly, like pull-down option lists, range checking, etc. There is also a version that runs on the Calc spreadsheet that is part of the OpenOffice.org office suite (also free).
While not created by me, there is another file that can be downloaded for free called Transmission Link Planning Tool, by Mr. Alok K. Tiwari, of Idea Cellular Ltd. It is a very useful spreadsheet that runs in Excel. Alok has been continually adding features.
Matching Network Designer is an incredibly sophisticated Smith Chart spreadsheet provided graciously by Mr. Manfred Kanther. Chances are you have never seen such a high degree of functionality programmed into Excel.
Although not to the level of the aforementioned spreadsheet, I offer my own Smith Chart for Excel in two versions. One version takes complex impedance values as input, and the other takes S-parameters. It is a great tool for entering data from a product datasheet or from the output of a network analyzer.
Your suggestions for similar software or online calculators would be greatly appreciated both by me and by other RF Cafe visitors. Because of the large numbers of e-mail that I receive, it would be nice if you would look on the Calculators and Software pages to see whether the item you are thinking of is already listed.