KW7 performance compared to the 102" whip

Compliments of Firestik® Antenna Company Technical Support Team

Copyright © 1996 Firestik® Antenna Company

In most (but not all) cases, the KW7 will out perform the 102" whip because of its design. The 102" whip radiates along its entire length, but mostly performs as a wave base loaded antenna (works better than a loaded wave because of the height and relative capture surface). The xmit pattern of the 102" whip (on an ideal ground plane) is fairly spherical which means that a portion of the magnetic wave propagation is upward, versus outward along a horizontal direction.

The KW7 antenna, although eighteen (18) inches shorter than the 102" whip, has about 265 linear inches of wire. Like all Firestik wire-wound antennas, the design is so that the magnetic wave field strength is greatly heightened at the uppermost portion of the antenna where it is most beneficial. The voltage at the base of the antenna is relatively low while the current is relatively high. As the current moves up the antenna it finds that the windings become closer together, eventually fully compressed against one another. The increasing intensity of the magnetic field slows the current and causes the voltage to drastically increase along the upper reaches of the antenna. If you have ever studied induction coil principles, you will understand the current/voltage relationship properties that are utilized in the design of wire-wound top loaded antennas.

Aside from the benefits of coil design, the KW7, as a function of its design, has a lower angle of radiation than does the 102" whip. Accordingly, the radiation holds closer to ground level over longer distances. When it comes to "skip" it is difficult to determine what antenna might work better than the other when communicating with a fixed location. For the most part, most antenna designs have a different angle of radiation. If you have ever played billiards you know that changing the angle where the ball initially hits a rail will effect the exit angle and location that it strikes the opposing rail. Unlike billiards however, the ionosphere layer that the RF signal bounces off of is constantly changing. One day you might be able to talk to someone 500 miles away and the next day, only those that are 1,000 miles away. But, if you change the antenna on that day, the angle of radiation of the different antenna might now allow you to talk to the station that is 500 miles away. If you find out how to control the ionosphere, you will leave this earth a famous person.

The 102" whip is a classic and it will always have a home in the CB marketplace. As far as we are concerned there are two main advantages of the 102" whip -- 1) They are fairly forgiving when it comes to problems caused by odd mounting locations and, 2) You can bang it into just about anything without worrying about damaging it. On the downside is the xmit pattern, angle of radiation and inability to utilize induction principles to increase coupling voltage.

The Firestik KW7 antenna is available in black, red, white or blue. The bench center frequency is 27.430MHz. The sub 1.5:1 SWR bandwidth is 1.5MHz (341% of CB band) for coverage from 26.680MHz to 28.180MHz. The finished weight of the antenna is 13.4 oz (380 grams). The balance point is 41.8" above the bottom or 1% above physical center.


Firestik Antenna Company - 2614 E Adams St - Phoenix, AZ 85034 - (Tel) 602-273-7151 - www.firestik.com

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