RF Column 42 - April 1995 Copyright (c) 1995 H. Douglas Lung ALL RIGHTS RESERVED TOPICS: Review of "The ARRL UHF/Microwave Experimenter's Handbook" Editorial - No future for analog TV? Competition from the 'Net How to find a company on the World Wide Web Big list of interesting Web Sites ----------------------------------------------- First, the column originally scheduled for this spot has been delayed. A combination of a bad cold which seems to be sweeping through Florida, two LPTV stations to build in the next two months, a new controller to design, build and test for those two station and a difficult subject matter made it impossible for me to finish up the path calculation spreadsheet as promised. Translating, converting to spreadsheet format and testing the formulas I found for distance / azimuth calculations on planets of various shapes (spherical, egg-shaped and FCC) turned out to be much more time consuming and much more difficult than I thought. If you want to forge ahead on your own, I'll tell you how to find some of the formulas using the book I referred to last month. Since I wrote my article on the future for over the air TV transmission several months ago in the year end TV Technology Buyers' Guide there have been several new developments that warrant an update. I'll cover some of the more important ones. Blue Earth Micro has a more advanced miniature controller than that I used in the Cheap Remote series last year. Its' the heart of my new LPTV remote controller and I'll give you an overview of some of the features. Finally, more companies and government agencies are showing up on the Internet. I'll tell you how to find some of the more interesting ones as well as pass along a tip on how to find companies' World Wide Web pages (WWW) even if you don't have their URL. The excellent, easy to follow and inexpensive book on UHF and microwave engineering I mentioned last month is "The ARRL UHF/Microwave Experimenter's Handbook - Antennas, Components and Design". It's published by The American Radio Relay League, 225 Main Street, Newington, CT 06111-1494 U.S.A. Email Ltardette@arrl.org, telephone 203-666-1541 or fax 203-665-1166. Although this book was copyrighted in 1990, I didn't discover it until recently. Chapters that broadcast RF engineers might find useful include A Brief History [of UHF and Microwaves experimentation], RF Safety, UHF and Microwave Propagation, Microwave Devices, Transmission Media, Design Techniques, Notes on UHF and Microwave Systems Design, Microwave Fabrication Techniques, Antennas and Feed Lines, Getting Started in Microwave Measurements and, finally, Tackling Microwaves with Microcomputers. Hmmm... I named all but one chapter in the book! The one I didn't name, by the way, was titled "Earth-Moon-Earth (EME) Communications". The chapter on UHF and Microwave Propagation alone is worth the price of the book -- US$20, US$10 additional for a disk of programs in Basic related to the book. If you enjoyed my columns on microwave path analysis and want to go deeper into the subject, this book is a good place to start. You'll find out how to calculate knife edge diffraction loss and how to calculate the actual K factor at any given time based on current weather data. I also found the section on distance and azimuth calculation to be the easiest to understand of the four references I've used so far. The chapter on microwave devices also presents a clear, concise explanation of how klystrons work. I found the section on traveling wave tubes (TWT) a little too concise, but overall the chapter gives a good overview of how the RF components in your microwave or satellite uplink work. If you've ever have to explain to someone whose experience is limited to coax how RF can travel through a waveguide, the transmission media chapter offers more than a good introduction -- it will show you how to use a slotted line for RF measurements and how to calculate critical waveguide dimensions. It also covers circular waveguide, although if you want to know about high power UHF circular waveguide I recommend the application note from Micro Communications in New Hampshire (603-624-4351). Earlier I left out the chapter on Earth-Moon-Earth communications. If you operate a satellite downlink or uplink, you won't want to skip this chapter. It describes how to calculate your operating system noise temperature by comparing the signal received when pointed at cold sky and when pointed at the sun. It also tells you how to use the sun to calculate antenna beamwidth, although using an off the air communications satellite signal is probably easier for broadcasters. If you have any interest in RF above 800 MHz., buy this book! (No, I wasn't paid for this recommendation -- just a satisfied customer!) I hope you had a chance to read my article in the TV Technology Buyers' Guide that came out the end of last year. In it I said that unless over the air TV broadcast moved into the digital age, the future didn't look bright. I have to repeat that I'm not implying over the air analog TV will go away soon. I am saying that new technologies will allow other industries to take away our audience and economic base. By moving over the air TV into the digital age I was not referring to HDTV. I was instead referring to the new methods of transmitting real time digital text, graphic, video and audio information over computer networks. The best and most hyped model of that now is the World Wide Web utilizing the Internet. The World Wide Web (or WWW for short) is not a computer service like America On-Line or Compuserve. Instead, it is more like a virtual TV dial with many independent servers (or, to match the analogy, "stations") contributing different material. Most of it is education or government related. More and more of it is becoming business and commerce related. Web servers already exist that can transmit video and audio. The video isn't pretty, but its a start. The audio isn't bad if you have a high speed ISDN or better connection. You don't need moving video for some things. A few weeks ago one of the most popular sites on the Web was Sport Illustrated's photos from the "Swimsuit Edition". Last year the during the impact of the Shoemaker-Levy 9 comet into Jupiter the site set up to distribute scientific photos of the impact was completely overloaded with people trying to see this event. There is a growing demand for information of all sorts using the Web.. What does this have to do with over the air TV? Here are a few recent items from the news. Several major companies are petitioning the F.C.C. to permit use of the 28 GHz. band for digital point to multipoint transmission (broadcasting). While the F.C.C. ruled out use of the new General Wireless Communications Service at 4.6 GHz. for broadcasting, it did request comment on whether this should be allowed. Also, unlike most other microwave services, the F.C.C. proposed allocations based on coverage area. It's possible to transmit good video at rates below 5 Mb/sec. using MPEG-2 compression. In San Francisco one station is supplying a news channel to cable companies using a T-1 carrier -- 1.54 Mb/sec. Today compressed digital video permits up to six channels per 36 MHz. transponder. Given a 500 MHz. band at 28 GHz. you could broadcast quite a few channels! Of course, this would require multiple transmitters connected together with fiber. I see cable and fiber as one of the most direct threats to over the air TV (note I didn't say TV stations - someone is still going to have to do the news and produce the programming). As I've said in previous columns, I believe the vast majority of HDTV sets will be hooked up to cable. They will be too big to carry around the house, so why use an antenna? No cable? Use your "video dial tone". Why would advertisers and programmers move to a digital computer network offered over phone line, cable, fiber or microwave and away from over the air TV? Pick up a computer magazine or thumb through Broadcasting Magazine and you'll see a list of companies putting new WWW pages on the Internet. New companies on the Web include CBS, Sony, Levi's and Time.. These are aimed at consumers rather than computer experts. Once the bandwidth is available, the still graphics, jerky small screen video and limited audio will change to video and audio indistinguishable from what you see over the air now. The next step will be to add some interesting feature or programming to get people to view the ads. There's one big problem with the scenario and the local broadcaster could offer the solution to that problem. Earlier I mentioned some Web pages had become so popular that it was difficult to connect to them. As more people become connected to the Internet or whatever it becomes, it will become difficult to offer customized services to hundreds of thousands of people simultaneously. My idea? Let the local TV broadcaster take that 20 Mbs of capacity on their new channel and use some or all of it to carry the localized and the most popular national "son of Web" programming. Equip the receiver with enough disk capacity to store 12 hours or so of transmission. That's over a 100 Gigabytes, but given the rate at which disk capacity is increasing we should be there in five years. Transmit the sitcoms and soap operas anytime and let people watch them whenever they want. An optional MO drive for recording favorite shows could be an option. Now, to take full advantage of the wireless aspect of over the air broadcasting, use some of the data stream to offer real time information with limited graphics for sports, weather, traffic reports, special sales, financial data and news. Of course, all this could be sold to a sponsor, with a logo or small ad appearing at the bottom of the screen with a "click for more information" option. Sorting out all the various information, programming and products will be difficult. Someone will have to program the links to permit the viewer, for example, to easily travel from news, to weather, to weather in a distant city, to news about that particular city and back to a travel agency to book a flight. Developing a tie in with the new Cellular Digital Packet Data (CDPD) AT&T and McCaw cellular are installing around the country would permit instant feedback -- order something, request info on something, complain about something. Getting back to 1995, here are some new sites of interest to broadcast engineers to check out on the World Wide Web. I received this info from John Neuhas: "I've posted a page on the World Wide Web to make it easier to find documents in the FCC server. Usually, I read the FCC Daily Digest and when I find something I think is interesting, I put it's address on this page to make it easy to get back to the document. The entries are those that relate to my own interest in radio communications. My FCC index is at the following URL: http://www.planet.net/fccindex " John also has links to other RF related pages on the Web in his page. To find out what AT&T is up to, check out their elaborate server at "http://www.att.com". I received a questionnaire from Tektronix asking for ideas on a Tektronix homepage. It appears they are working on something. Trying to connect to "http://www.tek.com" gave me "ERROR 403 - Forbidden - Server refuses to serve your IP address". It looks like something is in the works, just not ready for the public yet. Maybe it will be by the time you read this. Hewlett Packard is on the net and their test and measurements division is represented. Check out "http://www.hp.com". Satellite users should check out "http://itre.uncecs.edu/misc/sat.html" for interesting satellite links. Finally, I got some requests for the address of the people offering the Southern California Traffic report. It is "http://www.scubed.com/caltrans/transnet.html". That server suffers from the overload problem I mentioned earlier. Expect difficulty during rush hour! If you want information on a specific company or government agency and don't have their Web URL, try doing what I did to find the AT&T page. I simply added http://www. to the likely letter identifier for the company, ATT, then attached .com to the end, indicating a commercial site. (Educational would be .edu, Government is .gov, countries outside the U.S. use a two letter country code at the end: au is Australia, uk is United Kingdom, and so on.) Just for the heck of it I tried harris.com, comark.com and thomson.fr but got no connection. If you follow a link to a site that looks interesting and you want to see what else is there, click on the URL box of your Web browser and delete all the address after the .com or .gov or country name, press return and see what pops up. While I'm on the topic of computers, let me tell you about Blue Earth Research's new programmable controller, the BE-485. I'm using it in my next generation of LPTV controllers. It offers 27 digital I/O lines, a 4 channel 12 bit A/D converter, 128K bytes of RAM (with battery back up) and a real time clock. It can also be networked using an RS-485 buss. They sell an I/O module that brings all the BE-485 connections out to screw terminal connections, a DB-9 serial port and a 1/8" power jack. You could build a simple remote controller by adding a modem and perhaps a few pots to adjust the A/D input levels. The price of the BE-485 is $299. The ST-485 interface board is $59. You can get a hardware package include both of these items, a power supply, an RS-232 cable , user's manual and pocket reference guide for $399.00. Blue Earth Research is located at 165 West Lind Ct. Mankato, Minnesota, 56001-0400. Telephone 507-387-4001, Fax 507-387-4008, BBS 507-387-4007. Last month I mentioned there was an effort underway to add a news group (USENET) for TV broadcast engineers. It looks like it is going to happen. Here's the latest news, as received from sci.engr.advanced-tv: From: robgc@freenet.edmonton.ab.ca () Newsgroups: sci.engr.advanced-tv Subject: Re: RFD:Sci.engr.television.broadcast Date: 1 Mar 1995 08:25:37 GMT Organization: Rob Chambers at Edmonton Freenet I've been putting the final polish on my RFD for the broadcast television group and the renaming of this group to sci.engr.television.advanced. If you have been following this thread, a month ago I posted a primilary version. The RFD which I will be officially posting to news.announce.newgroups in the very near future is almost identicial to that previous posting. The only additions including mentioning Micheals proposal for the rec.video.professional group, creating the sci.engr.television heirarchy which advanced and broadcast would be under (instead of sci.engr.tv) and adding a charter and rationale section for the name change of sci.engr.advanced-tv Rob Chambers. If you access USENET (you can do it from AOL, Compuserve, BIX or several other on- line services) please keep an eye on sci.engr.advanced-tv so that you don't miss the vote on this important change. Meanwhile, I'm seeing more and more non- advanced-tv traffic on that group, so you might find something interesting there anyway! Well, that's it for this month. By next month I should have my "Cheap Remote III" up and running, although with the more expensive computer and expanded functions its not as cheap as it was! I'll pass on some interface tips for the BE485 in case you want to try using it in your projects. I won't promise a finished path calc spreadsheet, but I'll have at least two more additions to it next month. Finally, I've received a lot of info in the last few weeks about new products companies are showing at NAB. Unfortunately, the March issue was out before I received them and this issue won't be out until after NAB. I might as well wait for my report from NAB in the June TV Technology to discuss them. I'm collecting a list of resources for broadcast RF engineers. If you have some favorite reference books, Internet sources or technical magazines, please drop me a note. The usual ways to contact me are: Email to dlung@gate.net from all services except Compuserve. Use 70255,460 if you are sending from there. You can telephone me at work - 305-884-9664 after 6:30 PM Eastern or fax me anytime at 305-884-9661. ------------World Wide Web Sites Mentioned--------------- John Neuhas' FCC Index: http://www.planet.net/fccindex AT&T News, research and more: http://www.att.com Hewlett Packard - info on all products http://www.hp.com Satellite home page - lots of links http://itre.uncecs.edu/misc/sat.html S. California Traffic Report (interesting technology!) http://www.scubed.com/caltrans/transnet.html Future Tektronix web page? (see article) http://www.tek.com --------------------------------------------------------- Copyright (c) 1995 H. Douglas Lung ALL RIGHTS RESERVED