That was mostly pseudoscience. Sorry, it's really not that complicated. It's a matter of having a d@mn good (low loss) antenna system, knowing what your equipment is capable of, and optimizing it to capture long-term data collection. Then doing extensive analysis on the data (parsing it, and sorting by different categories to examine trends) and maintaining a detailed database with as much information as you can fit. If you have done that over an extended period of time, trends will emerge. And if you have done this over many years, you should be able to spot new hits immediately, and also see the many changes that occur as agencies change and evolve...or devolve (that happens...it's all about operations and maintenance costs, as well as federal funding). Capturing NACs and UIDs make identification much easier (in most cases). Then you get to observe trends to breakdown sub-departments within the various agencies themselves. Scanners, like the TRX-2, can deliver most all of the goods...ENC or not. Add a PSR-600 type scanner with WIN500 logging to the mix, and you will be able to capture NACs on data transmissions...which other scanners won't do. Many systems belch data even when no one is talking, so that greatly speeds up the data collection and identification process.
The golden age of coordination, when agencies had national frequency assignments, is just about gone. The bands have become one big cesspool of poorly coordinated frequency reuse. And from my many travels around the country, and observation of different densely populated areas of the U.S., every area agency district appears to do their own thing. National standards are falling away. It's a shame to see that happening.
Could a DEA agent take his/her radio across the country and talk to all the various districts along the way? I doubt it. Maybe he/she could if he/she had enough space in his or her radio, and it was programmed with different zones for every district. He/she would have to know how to, and when to, change zones. Good luck with that! From what I hear, many agents don't want to know anything about their radios. Then they complain about how they don't work. You're lucky if one Agent in Charge knows how the system was designed and what channels to use.
And then there is the push for DEA to return to VHF. That's another complication. Here in Florida the old analog Micor UHF system went way beyond "end of life", and was not being maintained (funding issue). For many years they relied on direct analog simplex with Flint air support relaying the traffic. Some areas, like Tampa, starting building new VHF repeaters that are now (finally) in steady use (first to migrate). New VHF repeaters were installed and tested in other parts of the state, but have been slow to catch on. North Florida agents have finally discovered the new VHF system, but central and south Florida agents still use UHF analog. Perhaps the other areas are not yet completed on buildout. I have noticed techs turning up new DEA and ATF...and occasionally new FBI RA and/or USMS P25 repeaters in batches. I assume they are doing all planned build projects one site at a time, and are handling all agencies under their area of responsibility. That's a logical approach to save money. As far as I can tell, this is still WIP. Funding must be slow.
Getting back to DEA...Observation of the N FL system indicates some sort of automatic repeater selection that activates/deactivates repeaters as a group moves around. Agents can go a long distance, and never talk about changing repeaters, so it must be automatic. When a group splits into two areas, both areas light up. But the agents mentioned two distinct N FL zones indicating different regions, so how the system works with borders like that is unknown (at this time). Does Tampa have the same setup? Not that I have observed. They select the VHF P25 repeater for each area they work. Once again, every district appears to do something different. The only common frequency I have observed is 170.6500 car to car. And I have only heard one UHF P25 simplex frequency used around Orlando. It must be a "one off".
Due to narrow rebranding efforts, and the doubling of channels now available, now is a great time to search for new frequency assignments. Many agencies are taking advantage of this opportunity, and if they can get funding are stamping out new repeaters along with new simplex assignments. Agencies like the IRS are even returning to VHF after a long period of UHF abandonment. Heck, they just came up on a new repeater pair and new simplex frequency around my city a few days ago. But you have to be searching all the time with the right equipment (programmed perfectly) to catch stuff like that when it happens. I may not hear those frequencies active again until someone knows that they have them at their disposal and knows how to access them. Stuff can sit dormant for months, if not years, at a time. Still, I add them to my "listening" scanners and wait for that day. Most of the time it pays off. There's not much I miss, and if it's ITC, I get to enjoy the fruits of my labor. Fun hobby!
Phil