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Ok, so I'll take a stab at that question for you. The King County TRS (TRS = Trunked Radio System) has always fascinated me.

The entire system is really 3 seperate systems, but all linked together. The system architecture is something Motolola designed - really quite ingenious. The three systems are 1. Seattle system 2. EPSCA (eastside) 3. KC/VC (joint between King County, and Valley Com, VC is a really big PSAP for south king county).

Within these three systems are several sub systems. Each system has a "simulcast" system, and then several "IR" systems. The simulcast systems are the most well known in each system and carry the most radio traffic. They broadcast all radio traffic through all towers at the same time, and each simulcast system has it's own set of freqs (those three freqs, one each for Seattle, EPSCA, and KC/VC are very well known).

The "IR" systems (IntelliRepeater) systems are stand alone radio towers, that handle trunked traffic all on their own. They have their own set of freqs different from everyone else. They are used to fill in gaps of coverage where the simulcast system doesn't reach, or are also used to take a particular subsciber off another system (perhaps the simulcast system) and contain them to one geographic area (I'm just speculating there).

Now, the really cool thing about the system is everything is linked - according to radio and talkgroup that is associated with a particular system. I.E. when a Seattle Firefighter turns on his radio - it immediatly affiliates with a system (any system - probably the Seattle Simulcast system, but it could be any system depending on where he is). He then selects a talkgroup - and the system knows what talkgroup he's on. Then, when he transmits - everything he says is repeated on any other system that has somebody on it that happens to be tuned to the same talkgroup. And that's the case across the three main systems as well (all interlinked).

So - let's say someone is up on Snoqualmie Pass. There is a KC/VC IR site up there called Dodge Ridge. It's only used for just that area - because that area is so cut off from the rest of the county. When I scan that IR site, I mostly hear KCPD North (because, technically, that is their beat). That's about it - the site doesn't handle alot of traffic. BUT - say someone drove to Snoqualmie Pass with a radio, and tuned it to SFD Dispatch, and affiliated his radio with the Dodge Ridge site. Boom - all the SFD dispatch would now get transmitted through dodge ridge, and if you were scanning it, you would hear it too.

So - what you hear on each system depends on what users are affiliated with that system at any particular time. Seattle Apple Cove - I think SPD North Precint. ESPCA North - I'm thinking bothell PD? Kenmore stuff? EPSCA Ed Hill is Redmond PD. KC Dodge Ridge (already covered that!). Just listen to the sites in "open mode" on your scanner and you'll get a feel for what agencies use what sites. Most of the IR sites you need to be pretty close to receive them. You won't hear them far away. Ed Hill in Redmond was a perfect example. I actually had to physically drive to the exact site just to figure out what frequency it used (that was the only one that eluded me for some time. It was also using temp freqs that wern't in the FCC database).

There's an excellent write up on the system written by Wiz, who is the manager for the entire system for the City of Seattle. Take a look at it here: http://www.interceptradio.com/wiki/inde ... Monitoring
It's very well done.

So, I'll stop rambling now, that's probably way more info then you wanted. And I'm sure I got something above incorrect - so somebody jump in and correct me for any screwups! If anybody has anything to add, go for it!

--Andre...

Does IR have a control freq

Yep, all the IR sites have their own control channel freq, which is different from the Simulcast sites that also have their own control freq.

OK, thank you for the information. So to answer my question, putting in the North Seattle site does it help me listen to the Seattle site more clearly?

No, they are two different sites (when you say North Seattle - do you mean EPSCA North? Or Apple Cove? ) Those are different from the Seattle Simulcast system. Most scanners can only monitor control channel traffic from one site at a time. You will hear different stuff depending on what site you're listening too.