902
Member
I'm not sure about the first part of your statement. The only problem I'm aware of is data collision during multiple unit transmission. In my system, I programmed radios so that they are inhibited if another user is talking. They can be overridden with a keypress, but the possibility of destruction is much greater than keeping transmissions brief and not talking over others. This is a training issue. If there is an emergency, Deputies press the emergency button and the signal will be sent until it is acknowledged and the dispatcher is alerted, then all traffic is held.mondaro said:
The utility of P25 is in range recovery when narrowbanding. I can recover comparable distance to a 25 kHz channel (20K0) using 12.5 kHz (11K2) P25. I would not have chosen FDMA, and I think the standard is largely obsolete now, even as parts of it have only recently been finalized, but a 2 or 4 slot TDMA P25 Phase 2 may look more like OpenSky. That would be two or four SIMULTANEOUS conversations passing through ONE repeater! TETRA has been used in European law enforcement for years and is considered to be reliable and cost effective.
As for subscriber equipment and fixed network equipment, prices have become competitive across the various manufacturers. I was given an Icom portable to try recently, which was fully P25 at $1,000. I see no need to have a $4,000 radio for conventional applications. The initial procurement in our system consisted of XTS-3000 portables and Astro Spectra W4 mobiles. We now do some XTS-2500 and some XTS-1500 portables. I do not like what Motorola has done with mobiles requiring an XTL-5000 mobile to use a W4 head. That is a waste, except that personnel are trained on the one type of equipment already. Continuous duty public safety grade base stations cost about the same for analog or digital. There are also proprietary derivatives of P25 that some manufacturers can marry you into. Those have nothing to do with standards, just exploitations of loopholes. Those include "ADP encryption" (which Motorola was shamelessly offering as an $8 dollar option on each radio) and "Wide Pulse ASTRO" which has absolutely no spectrum efficiency gain. One particular manufacturer also likes to short-cycle equipment and firmware revisions (wonder who). Yet, there are other manufacturers and there are competent radio shops (and if an area doesn't have one, most manufacturers will bring their own for the configuration and optimization).
Poor system engineering and an inadequate commitment to supporting a communications system is what is apt to get people killed. That goes for the most complex digital system to a Motrac bolted to a desk.
Please tell me where these P25 problems are documented.
What's coming:
You have heard about all of the geniuses saying we are too much like little children to be trusted to operate our own radio systems, right? The inability to operate a relatively simple radio system pretty much proves that. In very short order, radio as we know it will be gone in a big sweep to implement CyrenCall (which has not died), or several other proposals that will create a 700 MHz broadband system that will be virtually unmonitorable. In fact, voice communications will be an application layer on that system. Somebody somewhere wants to make recurring revenue off your agency, and they are counting on Congress to create the environment for them to do so. You'll have NO control over that system. No input on coverage without buying more coverage, which that benevolent entity can use to sell airtime to other (non public safety) subscribers on a secondary basis. You won't even know when something on the network end affecting your operations is broken or when it will be repaired. There are many lobbyists working over special interest groups to get their buy-in. You'll see it very soon, if not already.
