bruce@pixar.com (06/27/91)
A unity gain whip for 800 MHz cellular systems is three inches long, not counting the ground plane. This means that a small whip could be mounted INSIDE, on the rear deck of a sedan and give adequate performance for an auto alarm transponder in an urban area. I have one of those 27 MHz Mobile Alert systems, and I use a hidden piece of wire inside the car for its antenna so that it can't be defeated by breaking off an external whip. I've also noticed that the window mount cellular antennas go on working in urban areas even with the entire outside part missing. In these areas, multipath is more of a problem than signal strength. I use a Hirschman "stamp handle" antenna mounted on the center of my car's roof with my cellular telephone. Its length from the car's roof to the tip of the whip is three inches or a bit less. It looks like a chess pawn sitting on the roof of the car (they even come in black or white!). The car is the ground plane. The window mount antennas are so long because they have have gain to fight the loss of that lame through-window capacitive coupling. I have a 5 dB gain whip that screws into the same base as the unity gain antenna, but it has not yet been necessary to use it (using GTE in the S.F. Bay area). Most cellular connections don't use all of the power of the transmitter in your car, which can be commanded to transmit at different power levels by the cell. I don't know if the cell can also reduce its own transmit power level. Bruce Perens