Making Sense of What You Hear- Part 2, by Hal2000

It would take thousands of words and dozens of illustrations to explain trunked radio systems. So, we will look at the thirty thousand foot level.

What the communications industry did was to take lots of frequencies, lots of transmitters and receivers, and lots of computers to allow lots of users access to communications. They did what the cell phone industry did. For a large metropolitan area, they would build a dozen or so transmitter and receiver sites and connect them together with fiber optics and computers. This system would consist of anywhere from 5 to 35 frequencies, depending on the size of the area and the expected number of users.

By using a hierarchical structure, assigning priorities to users, and lots of software they could pack hundreds of users onto a trunked system using the minimum number of frequencies. It is truly mind boggling how it all works, and it is really cool. But we don’t need to know how it works to take advantage of it. The thing you need to know about and remember is something called a talk group.

In order to monitor a trunked system, you need a new scanner. Unfortunately, this scanner will cost you a lot of money– generally in the area of $400 to $600. To make it easy on yourself, you will need software to program it with. Gone are the days of punching in a few frequencies and hearing everything that is going on.

The reason this scanner is so expensive is that in the transition from repeaters to trunked systems digital came into being. Gone is the old analog mode. Analog is what you hear on the old AM radio band. Analog voice is now converted to digital bits that are transmitted via radio. Almost all trunked systems are digital now using a mode referred to as P25. There are still trunked systems across the country that are not digital, but they are few and far between. Do your research.

Gone are the old scrambled transmissions. Since analog speech is converted to digital bits these bits can be transmitted as is or rearranged before being transmitted. If they are transmitted as is, it is known as an unencrypted transmission. If they are rearranged before being transmitted, it is known as an encrypted transmission. The way the bits are rearranged before being transmitted is done by a software key. This key is kept very secret and without it there is absolutely no way of unencrypting the transmission. The new digital scanners don’t have a way to use the key even if you knew what it was. Search the Internet for digital scanners.

However, we still have the same problem we had in the old days. The powers that be can encrypt all their transmissions and if you bought that very expensive scanner all you will have will be a very expensive paper weight, right? Wrong!

Remember when I said that hundreds of users are packed onto a trunked system? Since a trunked system costs millions of dollars, most law enforcement agencies can’t afford them. So they partner with all the businesses and anyone else who needs communications to help defray the costs. All the old individual repeaters go away, and everyone ends up on one trunked system. The simplex and repeater frequencies are repurposed for trunked systems.

What this means for us is that all the unscrambled people we used to listen to are still there, unencrypted, but on the new trunked system. But something else has happened that makes scanning better.

Remember our new phrase we learned earlier: the talk group? A talk group is just what the name implies. It is a group of people who share the same characteristics grouped together and given a number. This number is referred to as a talk group.

Talk groups are neat things. Law enforcement has used talk groups to further define their departments. Now everybody has a talk group. The dog catcher, the narcs, the beat cop, EMS, fire, and sheriff all have their own talk groups. One talk group cannot hear or talk to another talk group, so each individual talk group thinks they have their own private radio system. It really is pretty cool how it all works.

Another neat thing about talk groups is that they can either be encrypted or unencrypted. Where I live, only the narcs and a few other specialized talk groups are encrypted. This leaves all the other talk groups unencrypted, providing lots of things to listen to. All the non public safety users are unencrypted so you can still hear all the people you used to hear.

There is one caveat at this point. Different areas of the country look at things differently. There are five trunked systems in my area. One encrypts almost everything, one encrypts sensitive talk groups (narcs, special ops, et cetera), and the other three encrypt almost nothing. So you need to do your research before buying a digital trunking scanner to make sure there is something to listen to.

Remember I said your old analog scanner was ready for the trash heap? That’s not necessarily so. Generally speaking, only major metropolitan areas can pony up the money for a trunked system. Usually what happens is that a private or government entity will fund and build the system and then sell users air time on it. It’s similar to what your cell phone provider does.

But what about the small towns around where you live? They probably can’t afford to buy time on the new trunked system or the necessary equipment, so what do they do? They keep their existing repeater system. So you end up with two scanners– your old analog scanner programmed to the repeaters in the region around where you live and your new digital scanner set up to monitor the trunked systems in your metropolitan area. Lots of good information can be obtained using this method.

Okay, we have our scanners and we have searched and found stuff to listen to. Generally you can determine the agency you are listening to by the content of the conversations. It may sound like law enforcement or fire but for what city? There is a fairly simple way to determine who you are listening to on an analog system.

The FCC requires all transmitters to identify themselves at regular intervals. This can be done by voice or morse code. A lot of dispatchers will include the callsign of the repeater as part of their normal dispatching. But the identification of analog systems is mostly done using morse code. All preppers should be familiar with morse code and how numbers and letters are formed. You don’t need to be able to copy morse code in your head, but you do need to be able to understand the dots and dashes used to make up numbers and letters. Write down the dots and dashes you hear, and then look them up in a morse code chart to see what characters you have.

All local law enforcement and commercial transmitters have a call sign assigned by the FCC. These usually consist of two or three letters followed by three or four numbers. So all you need to do is copy down the call sign and look it up on the FCC website. From there you can see the reference copy of the authorization issued by the FCC. This document shows the actual licensee, call sign, type of radio service, issuing and expiration dates, the coverage area, and the frequencies being used by that system. It is a wealth of information and will tell you all you need to know about who you are hearing. (Go to, then select Licensing & Databases, then select ULS, then select search licenses, then select advanced license search. For searching, it is not necessary to register or log in.)

I need to stress that all of this information is public. You are not breaking any laws or doing anything surreptitious by viewing this information. Everything in the FCC database is public information. But before getting too excited, you will not find any information on the FCC website about government or military stations.

Morse code identifiers apply to analog systems. Digital systems are identified in a different manor in a way that is much too difficult to describe here. Don’t worry, because trunked systems are much easier to identify. Simply visit the radio reference dot com website and look up your city and state to find all you need to know about local trunked systems. You can also find information about your regional analog systems on radio reference. However, please always verify for yourself the information you find there.

In addition to your public and non public service agencies, there are several other things you need programmed in your analog scanner. These are FRS, GMRS, MURS, Citizens Band (CB), aircraft, and Ham radio frequencies. The basic nature of FRS and CB frequencies are short range transmissions. That generally means that if you hear someone on them, you can expect them to be very close by. Act accordingly. You can get skip communications on CB frequencies but with the sunspot cycle heading toward minimum, skip will be less and less likely. Search FRS, GMRS, MURS, and CB frequencies.

There is one more thing you need to know for your scanners. Ever since 9/11 there has been a great effort expended towards something known as interoperability. Whenever there is a large emergency event, resources are pulled in from surrounding areas to help. This caused a major communication problem, because there were only a few frequencies set aside for mutual aid use. Everyone had their own systems back home, but when they all got together they couldn’t talk to each other.

There are now a lot of frequencies set aside for mutual aid or interoperability use. These are known as NPSPAC (pronounced nips pack), VTAC, UTAC, ITAC, and 8TAC frequencies and are designed for multiple agencies to talk with each other. Activity on these can be analog or P25 digital, but they will not be scrambled or encrypted. Please be sure you have these in your scanner. Don’t be disappointed if you don’t hear much on these frequencies. You can be assured there will be lots of activity in an emergency situation.

Search the Internet for NPSPAC, VTAC frequencies, UTAC frequencies, ITAC frequencies, and 8TAC frequencies. Also search for NIFOG. This is the National Interoperability Field Operations Guide produced by the Department of Homeland Security. This is a booklet you need to have on your bookshelf. It has a list of all these frequencies and how they are to be used. It also lists the incident command frequencies and how they are used.

One more warning about listening to a scanner. You have to do it on a regular basis. You can’t buy one, stick it in a Faraday cage, pull it out after SHTF, and expect it to be of any value. You need to find what is in your area, program it into your scanner, then turn it on, and listen to it. Listen daily! You will hear things you don’t understand at first, but the more you listen the more you will understand.