A report by Doug Moran..with his updated Map of Proposed Towers (July 2012)
https://maps.google.com/maps/ms?msid=209482381320120716761.0004a3aa50f14ecb36fa0&msa=0
Report from the AT&T Open House June 20 on proposed DAS cell phone antennas for Barron Park (and elsewhere). Barron Park attendees included me, Art Liberman and Bob Moss (and possibly others).
AT&T had two engineers there who could answer the sorts of questions mentioned in the earlier messages (one that we had asked over a year ago). The engineer we were talking to said that this was the first time anyone had asked him about these sort of details, so apparently Barron Park _is_ different. Below is the info gathered.
1. The City’s database of cell towers had multiple errors. The relevant one was that it didn’t show AT&T using the tower at the VA Hospital (I have updated my map to reflect this). This tower provides coverage for much of western Barron Park. The proposed DAS antennas in BP follow the contour of the limits of the coverage of that antenna. EXCEPT, the antenna at the top of Matadero is intended to provide coverage for the nearby section of the Research Park. For the small coverage areas that DAS is intended for, AT&T prefers to put the antennas on telephone poles because those poles already have the high capacity link (optical fiber) to their network node, whereas adding an antenna to the roof of a commercial building involves significant costs for the additional cabling. I didn’t get an explanation for the Chimalus site (because we had already monopolized the engineer too much).
2. Although the AT&T presentations characterize DAS as having an effective coverage radius of 2km, the existing installations in Palo Alto (in the north) typically are about 1500 feet (0.46 km). This is based both on obstructions — trees and buildings — and anticipated usage levels. Separation between antennas is less than this, partly because coverage is not a circle (obstructions) and because eliminating coverage gaps means that some areas will be covered by multiple antennas. The separation for the proposed sites in BP is about 1300-1500 feet.
3. There is no dead zone (a “null”) underneath the antennas. This is a misunderstanding by the non-techies who give the presentations. The signal under the antennas is very weak _relative_ to the primary beam,but because underneath is so much closer, a weak signal is more than enough to provide a solid connection.
Aside: most diagrams of the signal strength from an antenna are highly idealized — there are “hot” and “cold” spots resulting from the antenna not being the idealized “point source”. According to the engineer, the DAS antennas do have these effects, but not over the thresholds that affect cell reception.
4. Summarizing from much earlier: DAS antennas have pros and cons. Because they are intended to provide coverage for only a small area, they operate at much lower power than conventional cell towers. Because the towers are closer, your cell phone does not have to use as much power to make and maintain a connection. It has been argued (by AT&T) that the benefits of having your cell phone radiating at a lower level during calls more than offset the effects of having the tower closer to you (which is always on). This is an argument I would tend to believe. Also, lower power usage during calls and data transfers translates into longer battery life for your phone/device. Additionally, since the area to be covered is smaller, it is argued that service can be more reliable because it is easier to predict demand.
— Doug Moran