But i am curious. What does a big city radio system need for high rise buildings like in NYC, LA, Chicago, etc.? Forget the encryption debate. Analog vs digital? More repeaters or in building repeaters? Didn't big city's used to require a in building repeater for big buildings?
Analog, digital, and encryption have nothing to do with it. That's just being used to push a specific agenda.
There are a LOT of variables, and the engineering involved is way beyond a hobby website, so take this as a view from 36,000 feet:
Two options:
1. Blast more power in from outside. This is an expensive approach as it requires a lot more radio sites for a repeated or trunked radio system. Even with that, it's difficult to penetrate modern buildings due to the nature of their construction. All building materials attenuate RF to some extent.
2. Boost signal from within the building. This does not rely on a super strong RF signal from outside. There are two ways to do this:
BDA (BiDirectional Amplifiers) or DAS (Distributed Antenna Systems).
BDA's are the cheap solution. It requires an antenna outside the building, usually a directional antenna, pointed at the radio site. That signal is fed into the building to an amplifier and the RF is distributed throughout the building. The "BiDirectional" part means it works in the opposite direction, too. The radios inside the building are picked up by the internal antennas, go back through another amplifier working in the opposite direction, and are sent back to the radio site by the antenna on the roof. Sounds easy? It is, on paper. In reality they are an RF nightmare. That RF that gets retransmitted inside the building can leak out and interfere with radio users outside. The RF can get back to the antenna on the roof and go into a feedback loop and not only break RF coverage inside the building, but take down the radio site completely. There are a lot of companies that will install these things. The designers are usually required to have a specific FCC issued GROL license, but that does not guarantee a good design. These systems can require a lot of maintenance and frequent adjustment. But they are relatively cheap (dollars per square foot of coverage). Problem is that the building owner is required to pay for installation and upkeep. So take one guess where the first place is the building owner tried to save money?
DAS systems can be designed so they tie into the radio system core directly. Much more expensive and not always suitable for a dense urban environment. Cost can be in the tens of dollars per square foot, they are much more complex and cost a lot more money. But they are also more reliable, less prone to interference issues, and generally perform better.
As above, the building owner has to pay for the system and upkeep.
NFPA requires that fire radio services have suitable coverage in buildings. Usually -95dB over 95% of the building plus the fire alarm/control areas. It is up to the local jurisdiction to actually make it a local requirement.
The NFPA requirements are well intended, but don't really do a good job of it. It's a very broad requirement that doesn't address the technology very well. It leaves too much up to the building owners and local agencies. Can be classified as "Great idea with the best of intentions.". Leaves out the "What could possibly go wrong?" part of the statement.
This technology is way behind where it needs to be. Almost like the technology is purposely being held back for the benefit of someone. (hint, hint, hint….).
There's better ways to do this, but the NFPA/local agencies haven't caught up.
Modern public safety grade LMR radios can link back to the radio system core via LTE or WiFi, which -can- remove the problematic BDA/DAS systems from the equation, and save building owners a lot of money.
There is NO easy answer to any of this. Anyone that tries to convince you there is has zero idea what they are talking about. It's not as easy as using a specific technology or avoiding using some feature on the radio.
