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Top message:  850 downfall by 155n8th   Oct 29, 2003, 6:32 PM

Replying to:  Re: 850 downfall by Rich Brome   Nov 3, 2003, 11:32 PM

Re: 850 downfall

by wb    Nov 4, 2003, 12:22 AM

Interesting fuss with Nextel, considering that PS used Nextel almost exclusively until just recently, for their cell phone carrier. But they tried to slap the frequency restriction on all the cell phone companies- not just Nextel. This ploy failed.

I will beg to differ. The 800-850 issue is not simply a swath of spectrum but are very specifically assigned frequencies within a given band. Those specific frequencies are assigned to specific users. My knowledge of how this plays out in the cellular world is a bit limited.
Both the old AMPS system and what is still currently used for PS in many areas are actually Analog systems.
With the advent of Digital systems the environment changed. Many police outfits in metropolitan areas are going into the digital realm, and they seem intimidated by the presence of cell phones where they want to go. In my personal opinion this fear is unfounded.
The frequencies themselves are assigned and distributed. The Control Channels used by the towers distribute the assigned frequencies with very little chance of an overlap occurring. In PS systems a minor problem occurs because they allow sharing across the board. I can hear most of King County broadcasts on Seattle frequencies. But due to talk group ids it is unlikely for King County PD to talk to Seattle PD although they are often using the same exact frequencies. Most likely it is this sharing routine that may be causing them some concerns regarding digital systems. I don't think they got all the bugs work out yet. They are still looking at the Analog model.
From what I have seen cell phone towers also operate off of central Control Channels but they use a different (superior) technique. The talk group concept is applied to ownership notions. Thus it is possible to talk on your cell phone, on specific frequencies, which are being provided by the towers, without someone else butting into your conversation. CDMA has taken this notion to an extreme and is highly successful in tracking each specific call while assigning the call to a string of frequencies. Here the id code acts as a Fed Ex trace signature.
I would guess that cell phone companies also have a type of shared frequency activity going on, or it would be impossible for someone calling on one company's frequencies to talk to someone else on a different company's portion of the 1900 swath, but my knowledge on the specifics of this is void.
Rich?

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