flydream777 said:
***Trunking systems aside***
What is the advantage of having a conventional 800 mghz system?? From my scanning experience, they are weaker signals, harder to pick up, shorter range... and not to mention the interference/rebanding issues...
Is this one of those "hey, it's new so I have to get it" fads, or is there a real substantial reason for using conv 800 mghz systems?
The advantages of 7/800 MHz are not about scanning. In fact, the things that make scanning good for other bands, such as VHF are exactly what ruins its use.
I'm sure there are a lot of people who are going 'WTF?' right now because what I said is sacreligious for scanning, and maybe a handful of people who actually get it. I like monitoring, and it's been my hobby for over 30 years, but this is my profession, too. From the professional side, it's not about scanners. In fact, telecommunications technology may whiz past scanner technology. The market is not so great that Uniden and GRE make tons of money on research and development for the latest and greatest. It's about responders first, scale of economy second (most people leave that out, but I'm only being honest - money matters). Some people will also insert security, but that's a different can of worms.
So, "what's the advantage?"
Here goes:
Frequencies below 512 MHz are "shared use." The four public safety frequency coordinators (APCO, IMSA, FCCA and AASHTO) for the most part try to do their best to minimize interference, but as far as the FCC is concerned, all licenses below 512 have absolutely no regional exclusivity. You may, someday, get someone up on your frequency and have no recourse but to share it. The Rules and Regulations tell you to monitor before transmitting to make sure the channel is clear. That *always* happens, right?
VHF High Band has a legacy of haphazard assignment. There are inputs on outputs. Outputs on simplex channels. Many agencies have a legacy of putting the biggest tower on top of the highest mountain in their area and cranking the power to cover their 10 or so square miles. Recently, I saw a request for a system for 350 Watts effective radiated power to cover 3 square miles! To scannerists' delight, these systems can be heard for MILES, but they create tremendous interference and preclude the frequencies for reuse within 100 miles or so.
The 7 and 800 MHz band (you should consider them as one contiguous band from this point forward), is EXCLUSIVE to the one licensee within the service area. There is absolutely no way that the FCC will allow another system to be constructed over another. Elaborate engineering models (Longley - Rice formula) must be constructed to validate that there will be no interference. NPSPAC frequencies (currently 866 - 869, but moving down 15 MHz to 851 - 854 MHz) are even more restrictive. They allow for re-use within a certain area and are administered by a peer review committee, not the FCC. The FCC merely approves the plan. In most NPSPAC plans, the 40 dBu coverage contour must fall within three (rural) to five (urban) miles. This is important because signals are directed in toward the served jurisdiction AND NOT out to the horizon. This is why these systems typically don't get heard as far as the 'top of the mountain repeater' systems. Bad for scanners, but good for responders. 700 MHz assignment is even more restrictive (with the exception of several analog channels, the entire band MUST be digital... they DON'T have to be P25, only mutual aid channels must be P25; along with a greater mandate for channel efficiency pushing toward 1 voice path in a 6.25 kHz channelspace equivalent) and encourages regionalized deployment.
These other bands also mandate spectrum efficiency. VHF conventional is tremendously inefficient. Whenever another agency within city, county or state government needs a radio system to use, it must find a frequency (trust me, that's impossible in many areas), get concurrence from others who use it, and then must build a complete radio system just for themselves. If they work 9 - 5, like a building department may, that channel is idle for 16 hours of the day, but can't be used by anyone else. In a trunked environment (and you can have trunked VHF, but a public safety trunked system on VHF is highly unlikely in any populated areas) on a higher frequency band, the new user would procure radios, program them and the system manager would assign a talkgroup and priority. They'd share the handful of frequencies used by the system. It's tremendously more economical, although it seems more expensive up front. The decentralization of VHF and non-trunked UHF add up actually to more money spent for less efficiency.
So, that's why. When I build a system, the thing that's on my mind is not the people who listen - even though that's been my hobby for a long time - it's the people who use. It doesn't really matter if the system can be heard 10 miles out of town, as long as in town it is as close to 100% (on subscriber equipment, not scanners) as economically possible. These days that will mean that higher-technology initiatives will no longer be received on the old Bearcat. While that's unfortunate, needs for better coverage, better efficiency and better capacity demand their use.