Trunking and cell phones (same thing, almost)
Now that you guy's mention it - it all makes sense. I just cannot seem to wrap my head around "affiliations" as apposed to broadcast communications.
Next thing you know television signals won't be available on air to view until someone tunes their television to that channel and requests to view it.....This whole process is rather counter intuitive!!
Paul
Paul - I'm so proud of you!! A month or 2 ago you would not have been able to even ask such a question. Look at far you have come!! About your TV signal, that's not a bad idea! Why broadcast it if no one is tuned to it? I'm mostly joking, but your on the right track. (how would the tower know if anyone is watching that channel - your TV does not SEND any info back to the tower like radios and cell phones do.)
Lets say you, your wife and 3 kids all have cell phones. They are on vacation at disneyland. You could not go cause you are on a business trip in Chicago. You have another child away at college w/ a phone, and another at home. All your phones would be connected or 'affilliated' w/ at least 4 different cell sites, right? Otherwise when you call, how could the system find all those particular phones? I hope at this point you are seeing some similarity to public safety trunking.
There must be thousands of cell sites between Chicago and Disneyland. If you were to call your wife, would you expect that every tower between you and her would broadcast your phone call? Of course not, right?
Now you want to call all of them at the same time because you have urgent and exciting news. (like the police do all the time.) Imagine if the cell phone company made it possible for you to call a whole group of people (ie: your whole family) at the same time. That would be really cool, right? This is exactly what Nextel did w/ their service. Many businesses like construction companies jumped right on it and love it.
Nextel acts like a cell phone company, but is actually a huge trunking system available to the general public.
Now you have placed a call to your whole family at the same time, using the 'talkgroup' number assinged to your family's group. How many cell towers should broadcast your signal? All of them across most of the country? Of course not, and let's hope not. Only the sites that your family's phones are 'affiliated' with would broadcast the conversation, as it should be (probably 4). It should seem obvious at this point that all the towers can not carry all the traffic. Don't you agree? Same concept, same issues, same conclusions. Now imagine you are all home and all near the same tower, so you are all affiliated with it. Now if you made the same 'group' call, probably only 1 tower (in Utah) would broadcast it. All those other towers are now busy handling other people's phone calls, and do not know or care about your's, because your group's phones are no longer affiliated with them.
Our scanners only listen - they are passive. They do not affiliate with any tower and they don't transmit and tell the system 'hey, I want to hear this group xyz, please send me a copy on my closest tower'. That puts us at the mercy of someone with a Ucan radio being in our area and on our talkgroup of interest. Quite likely along the wasatch front. Less likely in remote areas.
When I think about it this way, it makes complete sense. Hope that helps you and others even more.
Brent Christensen
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