Useful RF Help On the Net

When I started my RF Web site back in 1995, there were few with information on RF and TV broadcasting. Eight years later, almost any question about RF can be answered with a quick Google search.
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When I started my RF Web site back in 1995, there were few with information on RF and TV broadcasting. Eight years later, almost any question about RF can be answered with a quick Google search.

I took a few hours to poke around the Web looking for sites in which I thought you might be interested. Would you believe that there is free software you can download to receive, demodulate and decode ATSC 8-VSB signals on your PC? Longley-Rice TV propagation software tends to be expensive, but if you don't need features like population counts and interference analysis offered by commercial software, a free Longley-Rice program may work for you. Budget tight? How about building some of your own RF test gear? Need to know the latest FCC regulations? Check out eCFR, currently under development by the Government Printing Office. Finally, I found some sites that offer links to a wide range of tutorials on RF topics.

GNU RADIO

GNU Radio is open source digital signal processing software that runs under the GNU/Linux operating system on Intel-based PCs. According to its FAQ, the site gives "ordinary software people easy access to 'hack' the electromagnetic spectrum, that is, to understand the radio spectrum and think of clever ways to use it."

There are a number of GNU Radio projects underway, although most of the progress seems to be with the FM demodulator and the 8-VSB/ATSC demodulator. The "Howto HdTv" wiki offers a step-by-step procedure for setting up the hardware, optimizing the ATSC signal and displaying the transport stream.

The FAQ, wiki and software are available from the GNU Radio software Web site at www.gnu.org/software/gnuradio.

Of course, some extra hardware is needed. Most of the current software is based on the Measurement Computing PCI-DAS4020/12 analog-to-digital converter PCI card. The "ultra high-speed" 4-channel 12-bit A/D converter features sample rates up to 20 MHz and costs $1,299. The RF frontend used in the GNU Radio receiver is the Microtune 4937 RF Tuner module. It offers double conversion to an IF frequency of 5.75 MHz (7.125 MHz in Europe).

There is work underway to use lower-cost A/D converters that connect to a PC's USB2 port, but it isn't clear if this will work at the sample rates needed to decode 8-VSB signals. If you are having trouble justifying the $1,299 A/D board for the receiver, look at some of the screen shots on the GNU Radio Web site. In addition to serving as an HDTV receiver, the software provides a spectrum analyzer display. With some tweaking of the software, I would think it could be turned into a very affordable 8-VSB/ATSC test set.

Take some time to browse the GNU Radio Web site and if you have the expertise and time, consider joining the project!

BUILD YOUR OWN RF TEST GEAR

Be forewarned-Green Bay Packet Radio's Web site at www.qsl.net/n9zia/ has the potential to be an incredible time sink! The amount of information here is amazing. The "Interactive Wireless/RF Design Utilities" include some useful utilities such as an antenna up/down tilt calculator (required on FCC microwave applications), a U.S. elevation retriever, and numerous RF path loss calculators.

If you're interested in hardware, some of the projects on this page include a portable antenna mast system, microwave oven magnetron experiments (check FCC regulations before proceeding with the "Thumpmobile-Zapper") and a 0-1,000 MHz spectrum analyzer with tracking generator. A scalar RF network analyzer for the spectrum analyzer is listed as a future project. More test equipment projects are listed on the "Homebrew RF Test Equipment and Software" page at www.qsl.net/n9zia/wireless/appendixF.html. One particularly useful but not-too -- tough -- to-build piece of gear is a return loss bridge. There is also a simple pulse generator for TDR (time domain reflectometry) transmission line/antenna analysis.

Reading about these projects is interesting, even if you have no immediate plans to build any of them.

LONGLEY-RICE PROPAGATION

I had thought about trying to put together some free software based on the Irregular Terrain Model, commonly known as Longley-Rice ever since I found the code on the NTIA Web site. However, the commercial Longley-Rice software I have works great and since my time is very limited I never got around to it. I'm pleased to see someone has found the time to put together a very workable program to calculate field strength using Longley-Rice and display the results on a map.

Radio Mobile is freeware written by ham radio operator VE2DBE. It runs under Windows 95 or later versions and uses elevation data available for download a no cost from several sites. Radio Mobile can use the 1 arc-second (30m) resolution elevation data from the space shuttle radar topography mission.

I have't had a chance to download the program and play around with it, but looking at the files it appears the program does support entering both antenna azimuth and elevation patterns.

You can download the program from www.cplus.org/rmw/english1.html. Other ham radio operators and clubs have contributed files and documentation to the project and there is a Yahoo group for discussing the program and its use.

FREE UP-TO-DATE FCC REGULATIONS

FCC regulations require broadcast stations maintain a current copy of the FCC Rules and Regulations. The Government Printing Office offers FCC rules in paperback format once a year and several companies sell copies of the rules and subscriptions for regular updates to the rules as they change.

If you don't subscribe to one of these rules services but need to find the latest version of the FCC rules, a beta test Web site from the National Archives and Records Administration may help. The site, www.access.

gpo.gov/ecfr/ allows searching the current (within 48 hours) Code of Federal Regulations (CFR).

FCC Rules fall under Title 47 of the CFR. Using the drop down menu list at the top of the page under "To browse contents, choose a title from the list below", select Title 47-Telecommunications and click "Go." This will bring up a list of all volumes of the FCC regulations. Broadcasting is under Part 73, which is shown in Volume 4. Click on 70-79 under "Browse Parts" to see a list of the Parts. Clicking on "73" will take you to part 73, where you will see a list of the section and the areas they apply to. If you want to see all of part 73, perhaps to download or print, click on 73.1 and when it appears, click on the link at the top that says, "View part." Do not try this on a dial-up connection unless you have lots of time. After awhile all of Part 73 will appear in a Web page with a list of subparts and sections with hyperlinks. After the table of contents loads, the entire text of Part 73 is displayed.

Some tables and formulas have links to higher resolution, more detailed images in PDF format.

Save the Web page to your hard drive and you will have an up-to-date set of FCC rules you can refer to anytime.

RF TUTORIALS ON THE WEB

If you want to learn more about RF and electrical engineering, Michael Ellis has put together an excellent set of tutorials on a wide range of topics, many of which he wrote and many more from other Web sites. His Web page also has a listing of on-line engineering courses offered by U.S. universities, including links where available. Michael Ellis's home page is http://members.tripod.com/michaelgellis/. The link to the tutorials is in the top menu bar.

Agilent has information on their measurement products and how to use them at Agilent Application Central: http://www.measurement.tm.agilent.com/appcentral.html. Under "Instrument Fundamentals" you will find links for information on Network Analysis, Time Domain Reflectometry, Spectrum Analysis and more. For example, click on Network Analysis and under "Events" you will see listed an eSeminar: "Back to Basics-Learn RF Network Analysis Basics." Click on this and you will find links to order CD-ROMs of the course and links to archived eSeminars. You will have to register with NetSeminar services to view the archived eSeminars.

CAVEATS

Many of the Web sites and programs described above were created by individuals or groups to help other people interested in this technology and not for money or profit. Keep this in mind when viewing the sites and especially when e-mailing the authors for help or information. If you have expertise you can offer to support these projects, especially ones like GNU Radio, your assistance will be welcome.

Your comments are always welcome. Drop me a note at dlung@transmitter.com.