First the software which used to be located at CPLUS.org is Radio Mobile Freeware by VE2DBE and is still at the site http://www.cplus.org/rmw/english1.html. It is different from the RadioSoft-RadioLink program mentioned in your follow up e-mail. The RadioLink program is a point to point software only. Second, the Radio Mobile Freeware program DOES NOT perform predictions just like dBPlanner or any other program with the exception of EDX now owned by Comarco. Radio Mobile and EDX both utilize the ITM model. A bit of history here... the ITM (Irregular Terrain Model) is basically Longley-Rice with some modifactions made by George Hufford at the ITS in Boulder, CO. For those not up on propagation models, this was the de-facto standard in propagation modeling reccomended by the FCC until a few years ago. It predicts with a typical standard deviation of 10-14 dB. Longley Rice is a semi-empirical model and does not require feeding in drive test data to "calibrate" it. Most other tools on the market use a completely impiracal slope-intercept model like Cost231, Hata, Lee, Okumura, or derviations of these. These models are simply far-field, straight line models that are "tuned" by going out and setting up test transmitters, driving around and collecting signal strengths, then inputting these into a tuning algorithm which makes adjustments to the slope and intercept points until the line "best-fits" the collection of data. Lump sum losses can also be added in "post-prediction" to try to make up for things like clutter losses. These models, depending on the engineer who tunes them, can have accuracies as low as 7 dB, but this is rare. Typically, standard deviations are from 9-14 dB. To achieve lower, it requires extreme care in setting up and conducting the drive test, and to be accurate for every site in a system, a seperate drive test must be conducted for each site. In my opinion, if you are going to drive every site, why do you then want to go and approximate what you already know is there. It doesn't make much sense, but then most people who use these models obviously are not too concerned with accuracy or simply don't know any better.
Now, I'm no dBPlanner fan, and in fact am a direct competitor to them, but I feel that I must defend them on this matter. dBPlanner, in its infancy, used only one model, the CRC-PREDICT created by Dr. James Whittaker of the Communications Research Center in Canada. This model is a truly predictive model based on the theories of physical optics (Freznell-Kirchoff wave front base on Huygens Pricliple for those who care). It predicts with typical accuracies of 5dB standard deviation or better when used with high resoution (30m) terrain and clutter databases. It requires no drive testing for "calibration". There are only two tools in the world which currently use this model, dBPlanner and our tool Athena. dBPlanner has since sold themselves short, and inspite of hiring Dr. Whitaker away from the CRC to help them, they went ahead and implemented several slope-intercept models as well. They still call the CRC-PREDICT their "flag ship" model, but the others are available if one chooses to use them. Now, if you are still reading, you may be wondering why others have not implemented the CRC model if it is truly superior. There are several reasons. First, most of the RF tools on the market were written by programmers and not engineers. It is doubtful that there are even people within these organizations who even understand the true nature of propagation modeling or could explain what the differences are in modeling techniques. Second, it is expensive to reprogram a tool to use such a model. It requires knowing what the model is doing which brings us back to the first point. Third, everyone sells their tool as the most accurate (especailly if the client buys some additional engineering services to drive test and tune the models). If these companies start selling a tool which doesn't require drive testing, they are going to loose a lot of revenue. Fourth, if they admit the CRC is a better solution, their clients may jump to one of the tools who already implements it instead of waiting around for them to implement it. Fifth, and perhaps most important, Marconi has arranged an exclusive licencing arrangement with the CRC so nobody else can license source code. Since our license predates their license and we have a sub-licensalbe source code license, we are currently the only source in the world to obtain the model. We don't give it away and most of these companies won't pay for a model despite the accuracy. So, to say the freeware provided in the previously mentioned links predicts just like the "expensive" tools is incorrect. However, if I didn't have a tool and were looking to run some predictions on one or two sites, the Radio Mobile Freeware would not be a bad choice. I would trust its results over an uncalibrated slope intercept model any day. My suggestion would be to use as high a resulotion terrain as it allows...currently the SRTM data which itself is quite expensive outside the US. Also, the program does not account for clutter which can have dramatic effects on the propagation attenuation. So, my advise is....be careful in depending on these results for any high level engineering. Cameron Crum [EMAIL PROTECTED] wrote: > There used to be a freeware utility @ CPLUS.Org I went there today and it >looks like a different company. This program lets you bring in DEM files and performs >radio predictions just like the expensive programs like dB Planner. Luckily I saved >the program and the website for future reference. I can upload it to my FTP server if >you would like to try it out. > > Jerry > > -----Original Message----- > From: Juanse [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, February 18, 2003 12:19 AM > To: MapInfo; [EMAIL PROTECTED]; > [EMAIL PROTECTED]; [EMAIL PROTECTED] > Subject: MI-L Off Topic: ham radio modeling over open source > > Hi every one and sorry before hand for this off topic requirement > > Under a non profit organization sponsoring we are developing an internet access >system for isolated school based on ham radio data transmition. On this effort we are >looking for any info regarding the siting of antenas /repeater. We would like to >explore the modeling of the signal taking care of topography to define the best >arquitecture to supply all school at least cost. > > We have 1:50.000 digital topographic maps of the study area, and it available either >through mapinfo/vertical mapper or postgis/mapserver. > > Under our preliminary research there are a couple of comertial software on the range >of US$500 to US$5000, and some basic possibilities under opensource (like splat >http://www.qsl.net/kd2bd/splat.html). > SPLAT! imports topographic data in the form of SPLAT Data Files (SDFs) that may be >generated from a > > number of information sources. In the United States, SPLAT Data Files are most often >derived from U.S. > > Geological Survey Digital Elevation Models (DEMs) using the usgs2sdf utility >included with SPLAT!. > > Any one know of tools to derive DEM like the ones need by splat SDF from contour >lines? > > Any one knows of other open source tool that could be usefull for our purposes? > > Sincerely > > Juanse > > temuko-Chile > > --- > Outgoing mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.449 / Virus Database: 251 - Release Date: 27/01/03 > > --------------------------------------------------------------------- > List hosting provided by Directions Magazine | www.directionsmag.com | > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > Message number: 5572 --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 5579
