Tower / Frequency Affiliation Explanation

Short explanation:

H= Home    D = Denied   A = Affiliation Allowed  ( "A+" at least 50%  or more of traffic compared to Home, "A-" less then 50%).

Long Explanation:

As explained in the How It All Works FAQ, ARMER is made up of several different radio systems operating together within the same shared protocol and network.  Each system may use from one to a dozen radio towers to cover a geographic area.    The key thing is that each tower is broadcasting the exact same information, on the same frequencies, at the same time, called a "simulcast system".   In some cases a governing agency may have multiple systems, for example Hennepin East and Hennepin West.   These are two distinct and separate systems, even though they are operated by the same agency.   Each one has it's own group of towers, operating on the same frequencies.

Also, every radio in the network is identified by a six digit address.   This address is broadcast every time a radio is turned on, transmits, changes channels, or tries to log on to a different system.   A master computer keeps track of every radio that is signed in, what system is is operating in, and what talkgroup it is tuned to.  

Generally speaking, every radio is assigned a "Home" system where it expects to do the majority of it's business.   The home system is fairly intuitive, a Minneapolis user (PD, FD, dog catcher, etc) would have the Minneapolis system (T109) as it's "home".    An Anoka County user would be on the Anoka system (T102).   Because of the size of Hennepin County, they have split their system into two, so a west metro department like Mound would be on the West system (T202), while a east metro department, say Edina, would be on the East system (T201).    State agencies and regional agencies like State Patrol, MnDOT, Metro Transit, and EMS providers, are usually assigned to the MN Metro site (T01).    From a consumer scanning perspective, programming the correct Home system for the talkgroup to be monitored is very important if you want to catch all of the radio traffic.

What happens if a user travels beyond their Home system's coverage area?   Some talkgroups are allowed to "roam" on to other systems.   Not only does this mean that the user is able to communicate on their resource, but all traffic on that talkgroup is also simulcast on the guest system until that user signs off.   While this is all may be seamless to the user, it can cause problems with the guest network.   

The whole concept of trunking depends on the fact that not everyone is talking at the same time, so by using a central computer to control access and share a pool of frequencies, it's possible to maximize efficient use.  But if too many roaming users are logged into a guest system at a time, and each one is bringing it's talkgroup baggage, the pool of frequencies can be used up quick, and legitimate users may not be able to transmit.

So, for that reason roaming is discouraged as much as possible without causing harm to the safety or effectiveness of the user.   Some users have no choice, their areas may cover such a large geographic area that they cannot operate without roaming.   State Patrol and metro EMS agencies are examples.     In other cases however, there may not be a legitimate need for a user to still have access to their channels while outside their area.  For example, a Minnetonka public works supervisor commutes to his home in Woodbury.   His "home" channel Henn East would provide effective coverage for his work area.  But if he carries his radio home, he would be out of radio range of Henn East.  His radio would have to roam onto MN Metro, and then Washington County.   While this is technically possible within the system, it doesn't make much sense to take up a valuable frequency slot on two other systems for a low priority user simply so he can still "be in touch".    In this case, the master computer will be programmed to deny affiliation of this radio and this talkgroup on the MN Metro and Washington County sites.    Because he is still within the ARMER network, he can still access a 911 Hail talkgroup in case of emergency or the A-TAC series if it's a major incident, but he will not be able to transmit or receive the public works talkgroup until he gets back in range of Henn East.

It can be also a matter where multiple systems may be operating within the same geographic area.   Each users radio is constantly scanning and comparing the received signal strength of all the data channels it recognizes as part of the overall network.   The user may enter a hole where another system's data channel has a stronger signal then their home.   It is up to the system administrators to balance the safety needs of the user in the hole vs. the safety needs and channel load of guest system.    If this roaming occurs too often and results in a home user not being able to transmit then limits may be placed on roaming.    For example, both the MN Metro and Henn East systems have towers in Downtown Minneapolis.   A security guard at the main jail should expect to be on the Henn East system, however if due to a fluke of radio reception, at one particular spot the MN Metro system might have a slightly stronger signal her radio will try to affiliate on to that system.   There isn't a urgent safety need for this to happen, the Henn East system still provides adequate coverage and the MN Metro system is extremely busy, so that master computer is programmed to deny affiliation of radios on the jail talkgroup on MN Metro.   From a consumer scanning perspective, it would be useless to program the jail talkgroup on the MN Metro system - you will not hear traffic on this group of frequencies, it would have to be programmed as part of the Henn East system.

In some cases the decision might be "to split the difference".   Mpls PD channels 1 & 3 are allowed to affiliate on T101 but denied on T201, but Mpls PD channel 2 is denied on T101 but allowed on T201.   This allows a system back up for a busy user but splits up the call load between two other systems. 

"Scanning" vs. "scanning"  - Scanning other talkgroups is allowed to some extent with a digital radio, most allow a scan bank of up to 10 other talkgroups.  Unlike a consumer scanner however, digital radios don't allow users the ability to scan outside the system they are currently signed onto, usually their home system.   If this was allowed to happen, the digital radio would have to disconnect from it's Current system to sample the data on another, this disconnection time opens the potential to miss traffic on their primary channel.    Referring to the previous paragraph, this means that a State Trooper, logged in on MN Metro T101, could scan Mpls PD 1 & 3, but not 2.   They could still have MPD 2 in their scan bank, but they'd never hear any traffic since that talkgroup is not allowed to affiliate on to the T101 system.   It is possible for the Trooper to talk on MPD 2 by "Forcing" an affiliation of MPD 2 onto T101.   Whether their radio is allowed to Force affiliations is a privilege that is assigned to their radio ID.    

X-TAC talkgroups (ATAC, ETAC, PTAC, STAC, etc)  -As far as I can tell, the X-TAC channels are allowed to affiliate on whatever system the radio user is currently logged on to.   Because the TAC channels are designed for events only, very few portable or mobile users keep their radio on a TAC channel.   This means that there is no guaranteed system to listen to to get all of the TAC channels.    The T101 system does seem a good bet for the E-TAC series because most of the Metro EMS users are on MN Metro has their home.    The best bet for a scanner listener is to program the X-TACS and Statewide mutual aid patch channels (MINSEF, MIMS, etc) into EVERY system they monitor.   This results in a fair amount of duplication, but it seems to be the only way to not miss radio traffic.

General rules - Some general assumptions can be made in what groups are allowed rights to roam, mind you these are just guesses.

Public Safety Dispatch (PD/FD) - Restricted roaming rights (high priority, but high also high usage).   Decision to allow roaming based on call load of guest system vs. necessity of allowing roaming.   If roaming is required due to poor signal coverage vs. slight drops in coverage.

Regional Safety Dispatch (State Patrol & EMS) - Allowed to affiliate on any system with little limitations.   Traffic frequently carried on multiple systems.

Police car to car & tactical - Restricted roaming rights for day-to-day "chat" channels (assumed low priority traffic, moderate usage).   SWAT and high priority tactical talkgroups allowed to affiliate (higher priority and less usage)

Fire tactical - Generally allowed to affiliate on nearby systems (high priority, little usage).   Mpls Fire is an exception, most likely due to the high traffic load and the assumption that the Mpls T109 tower should provided adequate signal coverage for the area of responsiblity.

Public Works - Restricted roaming rights (low priority, moderate to high usage).

Statewide TAC & Patch channels - Generally allowed free affiliation (high priority, low usage).

Copyright & Use Notice:  Information contained on this website is protected by copyright law.  Copying this information to your own website is STEALING!   And charging $20 for it in book form is just downright pathetic.  This information is presented for personal use only and may not be reposted, reprinted, or retransmitted without permission from the Website author.  Small sections of text may be reposed under FAIR USE laws if  appropriate attribution is given.   In other words, please respect the amount of work it takes to gather, organize, analyze, and post all this stuff!  Don't pass it off as your own work please.

Back to Home

Corrections, additions, questions, comments?  Drop a line: [email protected]