Digital Communications
Guys:
It's a reality check time here. The APCO-25 digital systems, along with your cell phone, are digital voice. It's the nature of the beast that it is never going to be 100% reliable. If you are up north in the middle of the Huron National Forest, or smack dab in the middle of Detroit, under the shadow of a cell or MSP site, just like your cellphone, it will always be flaky. It's digital voice. This is reality. Digital is great for data communications. If a byte get's messed up, the system sees a parity error, and simply sends it again.
Soon there will be fax machines on fire trucks that will have a blueprint and other info in the hands of every fireman as they roll to the call. Another system already being marketed is an optical reader that will mount on the side of a patrol car. The car will drive down the parking aisles on a shopping center, automatically reading 100 plates a minute, checking NCIC for stolen vehicles, expired plates, etc.
Many in-car video systems are now totally digital. A flash drive in the trunk of the car automatically downloads video data via rf to a hard drive the station when it is near by. (within 1/4 mile, according to an article I read in Mission Critical Communicaitons) No more changing vcr tapes in the trunk.
Digital data applications for first repaonders being developed will be amazing. Some of the stuff that FedEx and UPS are doing now is just as amazing, using handheld data terminals. I read a magazine article where UPS has a handheld data terminal that will automatically choose between which cell phone provider is closest, and use it's network to pass data.
But digital voice is not so forgiving. The data handshake misses a byte or two, and the voice is garbled up. And the system can't go back and retrieve it. It's real-time speech. And as frequencies approach 1 ghz, they will always be spotty. Just like your cell phone. How may people have laid two nextels together on a table, and had one with a green light and one with a red? It's the nature of communications as you approach 1 Ghz. Anything will absorb or reflect the signal, no matter how close to the site you are.
It's just the nature of the beast, guys. Digital voice, combined with using frequencies near or above 1 ghz.