RFBM's Radio Tower

RFBM's 60-foot radio tower is a big part of the operation. First installed as a 50-footer in 1995, this tower has been used in various configurations to hold the station's antenna array as well as serving several years as Black Rock City Communications antenna farm. From 1998 through 2000, the tower was installed in the Ranger Communications camp. In 1997, the tower was set up in only a 30-foot configuration. In 2001 ESDR Communications acquired its own crank-up tower, and RFBM has operated its own tower since.

A tall tower is necessary for effective FM broadcast coverage. Line-of-site operation is only one aspect of trying to place an antenna as high as possible. Line-of-site states that what you can see from the tower without land obstruction well receive a transmitted VHF signal. For a 60-foot tower, the line-of-site rule translates into an expected range of about 12-miles over perfectly flat terrain which exhibits the true curvature of the earth.

Elevation of the antenna is only one part of engineering radio coverage. The antenna system used can greatly enhance the receiver's perception of how the signal is being transmitted. Circular polarization has been used in the FM broadcast industry for decades. In real-world FM licensing, the transmitter's power is calculated to radiate a given amount of signal through a given antenna and a given transmission line connecting the transmitter to the antenna to achieve a specified signal strength away from the antenna. If the antenna is constructed in such a way as to radiate an expected horizontal signal and also an equal vertical signal, phased 90-degrees from the incident horizontal, then the antenna is said to be circular-polarized. The advantage to having the vertical component is that when the horizontal one reflects of an object or terrain, the vertical won't reflect the same way and will help to cancel the interference caused by the reflected signal at the receiver antenna. There are numerous designs for balancing the vertical and horizontal components and radiating them evenly around the antenna.

One antenna element is not enough, and several bays are stacked to improve the overall system gain. Adjacent bays are spaced a half-wavelength vertically from each other, which is not as good for system gain as full-wave spacing, but reduces the downward radiation near the site. The photo on the right shows a rare 1999 four-bay arrangement, although, in the end, only two bays were connected in this one. The standard RFBM antenna is a two-bay array connected with a 75-ohm, 3-quartrer-wavelength, coaxial phasing set; the simplest method available.

1999, ESDR camp is 90-deg from RFBM on the Center Camp Circle and so is the tower. The guying was strong and tight.

2002, BM Org-supplied tower, when BMIR and RFBM shared space. When powered lifting equipment is available, a maximum number of antennas and hardware are applied while it is on the ground. This minimizes the climbing work needed when the tower is up.

2003, The tower is a pretty versatile structure, allowing its height to be changed from 60-feet to 40-feet on site. This one was lifted by hand by station staff members.

This 40-foot configuration was cobbled together at the last minute to accommodate space restrictions for 2003.