Cellular Towers - Interesting Facts

[Bird]

I just read a book about wireless technologies and I learned a few things about the cellular towers. Some of it I already knew. Maybe some other people are interested in knowing.......

Do you remember when cellular first came out you would see all those towers that were a triangle on top of a tower with two antenna poles pointing down and one pointing up? Turns out those are omnidirectional towers meant to cover a large area and the two pointing down are the tower's receive antennas. The one pointing up is for transmitting to phones.

As more towers went up those were replaced (at least in non-rural areas like mine) with the ones with three vertical bars on each face of a triangle. The are called sectorized and cover smaller, better defined areas.
On that type with the 3 bars the center bar is the transmit antenna while the end ones are receive antennas. Also the distance between the two outside bars is set at roughly 20 times the wavelength of the frequency in use. For example the approx. wavelength for 1900MHz PCS is 6 in. so on a PCS tower the outside bars will be 120 in. or 6 feet apart. That means the receive antennas on a 800MHz tower will be even farther apart.
If there are only two bars, one is for trans. and rec. while the other is only receive.

Right now near my house there is a crew putting an antenna on an electrical tower. It has 2 bars on each or FOUR sides. Go figure??

Anyway, I thought it was interesting knowledge.

[larry]

Thanks for the info. I've noticed here in Los Angeles that Sprint, Nextel, and Verizon often use four vertical bars on each face of the triangle. Cingular usually only has two on each. AT&T will vary.