Doug Lung's RF Column

Issue #49 - December 1995


When I'm talking to other broadcast engineers or vendors, the most common question isn't "What do you think about HDTV?" (that's number 2). Instead, it's "How do you find the time to write those articles?" It helps tying the articles to project I'm doing as part of my job. This month's column is a good example of that. Last week I was at Andrew Corporation's Broadcast Antenna facility in Orland Park Illinois to check out our new Andrew TRASAR(TM) antenna for KVEA-52 in Los Angeles. Andrew's Kerry Cozad showed me how they tested the antenna and verified its performance without an antenna range. We also discussed the various options available to people purchasing UHF antennas today. That got me thinking it would be a good time to do a series on UHF transmitting antennas. On another matter, I received a fax concerning my article on pulsing in the October TV Technology. From that fax it seems some of my comments might have been misunderstood. I'll attempt to correct that. Finally, I'll give you an update on ways to connect to the Internet and information on a new service I'm offering (free of course) on my web site starting in December.

Antenna Choices

When Mario Lazzari, KVEA's Director of Engineering, and I were considering antenna options for KVEA, we had three choices -- a set of panel antennas, a top mounted slot antenna or a side mounted slot antenna. You probably surmised from the comments in the previous paragraph that I selected a slot antenna. Next month I'll give you the details on that choice. This month I'll talk about one option that's getting more attention as stations begin to think about Advanced TV -- panel antennas. If you are considering the purchase of a UHF transmitting, take time to review all the options.

Panel antennas have long been popular in Europe, where transmitter powers tend to be lower than in the United States. UHF panel antennas can be designed to be broad-band enough to allow several transmitters to operate on multiple channels with the same antenna. Unlike slot antennas, an array of panel antennas offers inherent redundancy. One or more of the panels can fail and the rest of the array will keep a signal on the air. A group of panels can be isolated for repairs while the rest continue to operate. Panel antenna arrays offer a great deal of flexibility in setting patterns. It is possible to synthesize almost any desired pattern by adjusting panel spacing and phasing. Beam tilt can be set independently for different directions, depending on where the population is. The downside to panel antennas is a high wind loading compared to a tubular slot antenna. This may increase the size and cost of the supporting tower. While it is possible to arrange a series of panel antennas around a tower for omni- directional coverage, the nulls are usually worse than those from a top mounted slot antenna. Pattern nulls can be minimized in large panel arrays by staggering the panels around the tower, so the nulls from individual bays do not occur in the same place.

When do I suggest the use of panel antennas? When several stations on widely spaced channels have to share the same antenna, panel antennas are the only choice. If a tall tower isn't required (that is, wind loading isn't a problem) and the desired coverage area has an odd shape, a panel antenna array may offer just the pattern needed. The broad-band response of most panel arrays makes them an ideal choice for a combination HDTV and NTSC antenna. If you are considering panel antennas be sure to check the power ratings for both the panels and the power dividers. The individual elements of panel antennas are typically rated for much lower power than slot antennas. Panel antenna assemblies multiply their power handling capability by using power dividers that split the power between the various panels. It is important to make sure the ratings of the panels and the dividers are not exceeded anywhere in the system. While this usually isn't a problem for single channel operation, it could become one if more transmitters are added to the same antenna.

Here's a final note on panel antennas. If you are using more than one panel, the "system" parameters are extremely important. If the signals from the individual panels are to combine to produce the pattern you expect, two things have to take place. First, if you are not purchasing the panels already mounted on a mast, the panel to panel spacing has to be exactly what the antenna manufacturer designed for. You can't blame the manufacturer for poor coverage if they designed the antenna for a tower with a two foot face and your tower has a five foot face! Second, the antenna panels, cables and dividers must be installed properly. If the installers swap cables or do not position the panels exactly as designed the results are often disappointing. I recommend you ask the manufacturer to color code the ends of each cable and the connectors on the antennas and power dividers so there is no confusion. It will also make it easier for you to verify the installation from the ground with binoculars.

Next month I'll discuss slot antennas and describe how Andrew Corporation tests their TV broadcast antennas without a test range. In future columns I'll take a look at what antennas are available today. If you're in the transmit antenna manufacturing business be sure to keep me up to date on your new products.

Mail and Complaints

Two months ago I described a low voltage pulser installation at KVEA and passed along a few tips on pulser setup. Shortly after the column was published I received a fax from Donald Adams, President of Advanced Broadcast Systems complaining I had unfairly characterized his product. As most of my comments were very positive, I suspect he latched on to my note on the appearance of the product, which I said "looked like it was built in someone's garage" and went no further. I realized he, and other readers, may have read more into that comment than I intended. As Mr. Adams pointed out in his fax, the unit he supplied was a custom product for KVEA's installation. Its case shouldn't be considered representative of ABS's other products. He noted that ABS is close "to having a production type control head for all non-ITS units [pulsers] with a delay board" capable of handling the delay introduced by the SAW filter (up to about 4 microseconds.).

I want to point out that the ABS circuit boards were professionally etched, masked and silk screened. In addition, in the test that counts, the system (except for the minor wiring error noted in the previous article) has worked flawlessly since it was installed. Indeed, I've found a home for KVEA's Marconi exciter and ABS pulser controller after KVEA's RCA transmitter is removed and replaced with the new Comark IOX transmitter.

Mr. Adams had another comment in the fax. He accused me of slighting smaller manufacturers. To that charge I can only respond that, as I alluded to at the top of this column, I write about products I use as part of my real job or have direct knowledge of. If I have slighted any company, it wasn't intentional. I can't sample every product, nor do I intend to simply parrot press releases, whether they come from come from big or small manufacturers. I use products which have worked for me before and I tend to buy from companies I've done business with in the past whose management and staff I know. Advanced Broadcast Systems is one of them. That doesn't mean companies I don't write about aren't as good or better than the big guys I write about. There isn't a lot of support around for older UHF transmitters and smaller companies like Don Adams' Advanced Broadcast Systems fill an important role in keeping these transmitters on the air.

Barry Taylor phoned me after reading the article. He has a small company in Miami building complete TV and FM transmitters for export and UHF power amplifiers for use in the United States. I stated in the October issue that one of the common problems I found in pulser installations was a lack of sufficient, clean RF drive to the tubes. Barry's company sells amplifier assemblies with power levels ranging from 1 watt to 250 watts peak output. His company, Transmitter Warehouse, is at 7310 Biscayne Boulevard, Miami, Florida, 33128. Telephone 305-756-7536 or Fax 305-757-4473. Several other companies whose main business is transmitters will also sell solid state amplifiers. Check the ads in this magazine.

I don't have the space to comment on every press release that I receive, I try to post all of them on my Internet Web site, the R.F. Page (http://www.transmitter.com). I welcome releases from all companies, big and small. There is no charge for it, but, because it is something I do in my "spare time" (what little I have) there may be some delays in getting items posted. Items that aren't especially relevant to TV RF technology go to the bottom of the stack. If the copy is clean and easily scanned, or, better yet, delivered electronically (text and graphics too if possible), it will get posted faster. I can scan a photo to include with the release. For an example look at the one from MicroCommunications Inc. about their UHF combiner. Although no company has sent me an HTML press release yet, I'm willing to give it a try. I should be able to post an HTML formatted press release on the RF Page within an hour of receiving it.

Internet Options

Since I started writing about on-line access several years ago and the Internet more recently, I've noticed a huge increase in the number of readers corresponding with me via e-mail. I've also noticed a big jump in the number of people using my Web page, which has only been publicized here and linked to from a few other broadcast related sites. It doesn't show up under Yahoo, Lycos, or Webcrawler, the major Internet search engines. In October my R.F. Page web site showed around 2,000 "hits", up from 1,500 the month before.

Back in 1994 I outlined ways to get on the Internet. Here's an update. Netcom has greatly improved their software and it now works with major third party Internet software such as the Netscape (800-469-0397) web browser. At $19.95 for 40 prime time hours and unlimited time weekends and midnight to 7 AM weeknights it is still a good bargain. Most of the problems I noticed accessing their numbers in cities like Dallas and Los Angeles have disappeared. Netcom can be reached at 800-353-6600 or 408-983-5950. (UPDATE - Netcom's Netcruiser now includes unlimited access time all day as well a special link for downloading a free copy of Netscape Navigator. Space for a personal web page is also included.)

If $19.95 is too expensive and 40 hours is more than you need, America On Line's subsidiary GNN has launched its Internet service after several months of free Beta testing. I took part in the Beta testing and, at the end of the test, was happy with the performance, both service and speed. Like Netcom, they offer a complete software package if you don't want to piece together your own set of (usually) superior tools. GNN's Web Browser handles the Netscape specific formatting I and many others use in their Web sites far better than the browsers included with Netcom's or Compuserve's service. GNN costs $14.95 a month for 20 hours a month (no free hours) but, unlike Netcom, includes disk space for a personal FTP and/or Web site. GNN's phone number is 800-819-6112.

For occasional Internet use, both America On Line and Compuserve now offer Internet access. Use WINSOCK as a keyword on America On Line to go to an area where you can download a "winsock" which will allow you to use many third party Internet programs, including Netscape, through America On Line's dial in numbers. AOL hourly rates should kick in after five hours but I've been told by one AOL user that he's never gotten a bill for Internet time. Obviously this could change. I've found AOL's Internet transfer times to be much faster than those on Compuserve. America On Line (AOL) can be reached at 800-827-6364.

Compuserve has recently revised its pricing and it now competitive with AOL for people needing limited Internet access. Unfortunately, the last time I checked Compuserve was much slower than the other services. It took thirteen minutes to download my PS- Squared page on Compuserve during peak evening hours. On Netcom, using Netcom's software it took a bit over three minutes. On Netcom, using the Netscape browser, I had a recognizable image and text in less than a minute. Hopefully Compuserve will improve the speed by the time you read this. Compuserve is the only service I've mentioned so far that offers international access numbers. In the U.S. the number is 800-524-3388 or +1-614-529-1340, in Bristol, England +44-117-976-0681 and in Hong Kong +852-599-2788. Compuserve has other offices throughout Europe, the Middle East, Latin America and Asia.

I haven't used Prodigy's on-line service or its Internet option, but I've heard good reports about it. Prodigy recently licensed Netscape's web browser and is offering it free to users of its Internet service. Prodigy's number is 800-776-3449.

I should list some other Internet service providers which I haven't tried. I've heard MSN from Microsoft isn't quite up to the other on-line providers in speed and service, but most people expect great things from it. MSN does offer international access numbers. They suggest contacting the local Microsoft office for details. U.S. Sales can be reached at 800-936-3500. Performance Systems International also offers limited International access as well as an inexpensive, unlimited access time Pipeline account. PSI's numbers are 703-904-4100 and 800-827-7482. Many of these services offer free trials. An excellent source of information on on-line services, rates and comparisons can be found at http://www.barkers.org/online/. This is a very competitive field so rates change frequently, usually down. (UPDATE - The ISP field is changing rapidly and by the time you read this much of the information may be out of date. Follow the links to find out the current story.)

If you want help setting up your account and if you stay in one place, you should consider a local Internet provider. (I don't want to be accused of slighting small Internet providers too!) Most cities have several and their rates are often better than those of the nationwide firms. Furthermore, if you have problems you have a much better chance of reaching someone who can help you. Some will come to your house or office to set up the software! Check local computer magazines or user groups for phone numbers. Many local Internet service providers include disk space for a Web page with the basic offering. That's how my R.F. Page on the Web comes to you, although by the time you read the RF page's move to a new dedicated Web site with more disk space, more speed and more programming options for nifty interfaces should be underway.

Next Month...

I'm out of space again! Next month I'll finish my series on UHF transmitting antennas. I'll also cover some of the technology I saw at the Private Cable and Wireless show in Miami. I see a place in this developing area for the skills broadcast RF engineers have gathered through the years. In December look for the launch of a new service on my RF Page Internet web site. As part of my job I have to keep track of developments in the industry and at the F.C.C. One way I do that is by taking advantage of the material available on the `Net. I've decided it won't be that difficult to "cut and paste" the links, add a brief summary and comment and post it to the R.F. Page. That will also allow me to distribute it to all our network's stations at one time. Take time in December to visit my R.F. Page and click on the link to RF Current, for a collection of news, opinion and links to stories on the net affecting broadcasters. I plan to draw material from the F.C.C.'s web site and the web pages of RF and broadcast related companies. Although it will appear in as a weekly edition, I'll be adding items daily when my schedule permits. Check it out.

Here are all the addresses and info you'll need to contact me. The RF Page is at http://www.transmitter.com and contains, among other things, a complete listing and full text (some with graphics) of past TV Technology RF columns and software since January 1993. The same items are available from my FTP site at ftp.transmitter.com/pub/. You can E-mail me at dlung@transmitter.com or phone me after 6 PM eastern time (when things quiet down a bit) at 305-884-9664. Both numbers are at the Miami Telemundo office, so expect a delay in a response if I'm traveling.

My mail service address is 2265 Westwood Blvd., Suite 553, Los Angeles, CA 90064. Because I'm often traveling, if time is critical (response required in less then ten weeks) please contact me for a local address before sending items by mail. Also, here's a reminder that I'm no longer able to offer the software programs I've written and mentioned in these columns by disk. They are available for downloading at by FTP site or through the R.F. Page, my Web site. As before, the programs are free. Enjoy the holiday season and take some time to remember why we are celebrating it. Best wishes for a memorable one!


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Copyright 1995,1996 H. Douglas Lung. All rights reserved

(Link to comparison of on-line services updated Sept. 22, 1997)