Over-the-air reception with an antenna can be a maddening affair. TV signal strength can vary dramatically with small position changes, especially indoors. Depending on your location and willingness to get up on the roof, it may take a great deal of tinkering to get an antenna system set up right.

My own TV antenna system is the product of a great deal of fiddling. The motivation is the start of baseball season in March. Oakland A's games are broadcast on channel 36 in the Bay Area, but channel 36 is not broadcast from the area's main TV tower. To bring in the additional channel, I needed to find out where to point the antenna, join it in to my existing antenna, and ensure that a good enough signal was available throughout the whole system. It required extensive experimentation, and it took quite a long time because of a demanding travel schedule.

Planning

To call my previous antenna a "system" is to give far too much credit to the single antenna I put in place as part of last year's TiVo project. I pointed it at Sutro Tower, the main TV broadcasting antenna in San Francisco. The single antenna served me well as long as it was connected to one receiver, but its shortcomings became apparent when baseball season started and I wanted to receive additional channels.

The first step in setting up a system is to find out how many antennas are necessary and where they need to point. In the United States, the best planning resource is antennaweb.org, a project of the Consumer Electronics Association. From a street address, AntennaWeb will use terrain maps and geographical information to show the direction to television transmitters, along with the distance. The calculations are based on relative altitudes and the terrain, and they will account for the differences in propagation between analog and digital stations, as well as the station's licensed transmission power.

After looking up the location, AntennaWeb will print out a table that has each station's call sign, channel, compass orientation, and distance. You can also get a street-level map that shows the direction to the transmitters in relation to local streets. Figure 1 is similar to the street-level map shown by AntennaWeb for the location of San Francisco City Hall.

Figure 1: Station map for San Francisco City Hall

For further information, you can use the use the FCC's TV query form to learn more about the transmitters. TV stations are licensed broadcasters, and must be granted the right to use a frequency. As part of that process, a great deal of information about the transmitter is made part of the public record, including the location of the transmitter, its power, and the direction its energy goes in.

Right away, I could tell I was in for a challenge. Table 1 shows the effective radiated power for the major stations in the Bay Area. The last two lines are for stations located on either Monument Peak or Mt. Allison, both of which are approximately 35 miles from my home.

*KNTV recently moved to a new transmitter; the values shown are from the construction permit for the new transmitter.
**The construction permit issued by the FCC was for 1,000 kW.

In addition to the close-in stations on Sutro Tower, I wanted to build an antenna that supported the digital transmissions of both channel 36 and channel 54. Luckily, both stations have digital transmissions that are close to each other: KTEH-DT uses channel 50, and KICU-DT uses channel 52. Both transmitters are close to each other, so a single long-range antenna should pick up both stations. The plan is quite simple: keep an antenna pointed at Sutro Tower, and join it to an antenna that points at Monument Peak.

The map printed out by AntennaWeb is most useful for pointing an outdoor antenna. With no obstructions, the directions indicated by the street map are relatively accurate. Indoor digital reception can be somewhat more difficult, and it often makes sense to point at a strong reflection. Directly at the source is not always the strongest signal indoors. I chose to keep my second antenna indoors because it is easier to tweak slightly, and I did not want to secure something to the roof. The penalty is that the house causes at least a 1 dB loss of signal, and probably more.

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