ComStudy 2.2 is a suite of RF study tools, the primary functions of which are the prediction coverage and interference, along with the study of AM and FM allocations. The software also supports TV and land mobile; however, my version does not support those functions. If I had to describe this software in just a few words, I'd have to say, “feature packed.

I can scarcely touch on every feature and facet of this program in a short space, but I will hit the high points of the most commonly used functions.

When it comes to FM coverage prediction, there are a number of variables to choose from. The first variable is the algorithm to be used: FCC 50/50 or 50/10 curves, Longley-Rice, or the yet-to-be-adopted point-to-point methodology, along with a few others that are less useful for FM propagation. Then choose the height of your receive antenna and the amount of environmental loss from foliage and urban clutter. You can also choose from a variety of terrain databases (30", 15" or 3") and even select the degree of detail that the program analyzes. Once the analysis is completed, you can assign a different color or hue to each of 36 different signal levels.

The FM Allocations Module is somewhat unique. When a set of coordinates is studied, the program analyzes all frequencies and all classes of stations each time. It takes the computer about three seconds to perform all this analysis. Once completed, you can quickly see which coordinates will fit. Channels that are fully spaced per FCC Rule 73.207 are highlighted in green, and those that can only fit using contour protection per FCC Rule 73.215 are highlighted in blue. This software is not a substitute for knowing FCC rules and policies, but if you have a good understanding and familiarity of Rules 73.201 through 73.215 and a little ingenuity, this software should be all you need to study and upgrade most existing channels and find new channels.

There are two ways to look at AM studies for daytime. The software can either produce a contour overlap map or a limits study.

For the contour overlap study, ComStudy searches the AM database for stations that are ±30kHz from the center frequency within a given distance, and then calculates all of the pertinent contours and displays them on a map. ComStudy assigns the same color for the service contour of your station and the contours of the interfering stations. You don't need to remember that the 0.5mV of your station and the 0.25mV contour for first adjacent stations shouldn't overlap. Instead, you simply look for overlapping contours of the same color.

The Daytime Limits study creates a file depicting the bearing and maximum inverse field allowable toward each co-channel and adjacent channel station, which can then be plotted on a polar map with the proposed pattern. Stations that are properly protected will show up in blue. Stations that are being interfered with will show up in red. With this same software module, you can get an indication of what would happen if the station operated with a different set of phase/power parameters and how that would affect nearby stations.

Conductivity information can be taken from the M3 data, or you can enter conductivity data from a previous proof, whichever is more accurate. Comstudy will recalculate the contours accordingly. You can even add towers, change their height and adjust the orientation of the array. This is certainly much easier than calculating several pages of vector math. Radio Soft even enables you to change parameters on the fly and see the results to the shape of the pattern in real time. With this tool, pattern design is less like engineering and more like a video game.

The AM allocations module is a very good tool, but should only be relied upon for daytime/groundwave studies. While there do not appear to be any errors in the nighttime/skywave study software, duplicate and erroneous entries in the AM database render it inaccurate in many cases, so those studies should be left to the consultants.

What if you needed to find a transmitter location that covers the city of license and the most populated areas, yet doesn't have prohibited overlap with other stations? There is an easy solution: use Drag and Drop, one of the most powerful tools ComStudy 2.2 offers. It allows an existing transmitter site to be moved to a new location by simply clicking on the site and sliding it to the new location. As the site is moved, all of the associated contours are updated in real time, allowing hundreds of sites to be analyzed in just a few moments.

The only knock about this program is documentation. Most of the functions and features within Comstudy 2.2 are either poorly documented or in some cases, not documented at all. This made it difficult to fully use all of the features at first. However, I did find the staff at Radio Soft willing to talk me through problems and functions over the phone. Better documentation is certainly needed; however, once you learn some of the secrets, it's a very powerful and useful tool. Not only does it provide most of the analysis tools that you need for AM and FM work, but it also gives you the ability to display them in a user-friendly fashion.

Jeff Littlejohn is vice president of engineering services for Clear Channel Communications, Cincinnati.

P 888-RADIO95
F 386-423-0821
W www.radiosoft.com
E pmoncure@radiosoft.com

Circle (204) on Free Info Card or go to www.beradio.com