KCBS Transmitter

We're off on the road to Morocco*...uh.. the transmitter. The KCBS transmitter site is in Novato, California. Novato is located in Marin County in the north bay. It is about a two mile drive on a dirt road out to the site. In the summer, cattle graze in the fields and have a tendency to walk on the road and slow you down. You can just make them out in the picture, they are on the right side under the big arrow with the word COWS floating above it. You can see all four towers and the transmitter building in this shot. From left to right are, towers one, two, four and three. The transmitter building is just to the right of tower 4.

Why do you have four towers? Good question. KCBS is a 50,000 watt, DA2. This means we broadcast with a power of 50,000 watts and use two different directional patterns. What is a directional pattern. You'll be sorry you asked but here goes. There are two types of AM radio stations. Omni-directional, a station that broadcasts its power equally in all directions from its antenna, or directional, a station that concentrates its power from the antenna in one or more directions and minimizes the power in another direction or directions. AM radio stations use directional antennas to maximize their coverage in a certain area or to protect another AM station on the same frequency or nearby frequency. In order to do this, a directional radio station uses two or more towers. We then use a device called a phasor (no relation to Star Trek Phasers) to vary the amount of power and phase relationship of the signal to each tower. The phase of the signal means the difference in time that one signal arrives at a certain tower compared to another tower called the reference tower. The vector relationships of the signals going to the towers add power in one direction and reduce power in another. Got all that? Good. There will be a quiz at the end of this page. Because of the fact that AM signals travel farther at night, a lot of stations use directional antennas to protect other stations by minimizing their power in one direction at night with a directional antenna. KCBS is a DA2. We use one pattern during the day with most of our power going South. In fact, because we re-direct the power that would be going to the North-East to the South, we actually end up with about 200,000 watts going South (major lobe is 148 degrees true). At the same time, we have about 12,500 watts going North-East to Santa Rosa. At night we use another pattern that reduces the power to the North-East to about 7,500 watts and protects radio station CBL in Toronto, Canada, which is also on 740 Khz. The fact that we re-direct power to the south and end up with more than 50,000 watts in that direction is the reason you can hear KCBS in Southern California and Arizona at night almost as well you can in the Bay Area (well almost as well).

OK. Now that you know all about directional AM radio stations and their components, let's go look at the actual hardware.

*Bing Crosby, Bob Hope, Dorothy Lamour--- 1942 Paramount Pictures--- Run Time 83 minutes. Check it out.

Updated 10/4/98