Are Philadelphia’s 2 P25 sites actually simulcast?

[jdm1]

I’ve been logging activity across all talkgroups in both of the Philadelphia P25 systems labeled as simulcast on RadioReference.

Site 1 doesn’t seem to pick up any police dispatch talkgroups, but does pick up a few talkgroups that Site 2 doesn’t pick up at all (PPA, PHL Emergency). Both sites pick up some activity on Fire and Medic channels.

Is RR wrong? And if so, what are each of the sites used for?

 

[u2brent]

I’ve been logging activity across all talkgroups in both of the Philadelphia P25 systems labeled as simulcast on RadioReference.

Site 1 doesn’t seem to pick up any police dispatch talkgroups, but does pick up a few talkgroups that Site 2 doesn’t pick up at all (PPA, PHL Emergency). Both sites pick up some activity on Fire and Medic channels.

Is RR wrong? And if so, what are each of the sites used for?

Each site carries different traffic.
1.3 NAC 3B3 EMS-Zone1
1.4 NAC 3B4 Law Enforcement-Zone2
1.5 NAC 3B5? Underground1
1.6 NAC 3B6? Underground2

Simulcast in this case simply means multiple towers making up each site, Each site (Zone) does not carry all traffic.
Zone 1 is EMS/Fire
Zone 2 is Law Enforcement
The "Zones" cover the same geographic area. Not like a north site and south site in this case..
Almost like two separate systems that co-exist, an overlay.

That's how I look at it anyway.. If that's of any help...

 

[jdm1]

Thanks, that makes a lot more sense. Still, there are a few oddities I've seen as I've listened into the two zones this weekend. Sometimes certain things come across one zone but not the other.

E.g. for PHL Police – occasionally (rarely) I'll hear a transmission come across Zone 2, but they always come across Zone 1 (which seems to be primary for this talkgroup). Also seeing this the other way around. Occasionally a PPD district transmission will come across on Zone 1, but it's rare.

Why aren't the talkgroups clearly split between zones?

 

[GTR8000]

Setting the system up so that talkgroups are only permitted on one simulcast cell (i.e. site) or the other without exceptions wouldn't be very wise. If one cell goes down, you want to ensure that everyone can operate off of the remaining cell, even if it means a lot of system congestion. That is why P25 systems have the ability to prioritize access at both the talkgroup and even subscriber (radio) level.

Simply put, if a radio happens to wind up on the Zone 2 cell, taking with it a talkgroup that normally is found on the Zone 1 cell, that talkgroup is going to be active on Zone 2 for as long as the radio is affiliated with that cell. As long as the talkgroups are not absolutely restricted to either cell, the possibility exists for that to happen from time to time.

 

[trentbob]

I listen to Philadelphia everyday Zone 2 with police and Zone 1 is fire EMS and city services. Citywide like J band, M band, T Band can be heard on both.

The database is incorrect and always has been, it is phase 1 not 2 simulcast and is very affected by LSM. It's best to program two different systems splitting the police and fire/ EMS so that you only have to scan one system at a time as it goes faster that way.

If you're using an SDS there are two different NAC numbers.

 

[trentbob]

I just want to add as I see the other 3 post are very informative. You didn't say exactly where you are in the city?

I never had good luck with the x 36 radios and the GRE Whistler radios didn't work well at all on the P1 simulcast systems.

I ended up using an apx 7000 which works terrific all over the city including Underground Transportation tunnels.

I also use an SDS 100 now for Philly. I focus on the far Northeast police district 7 and 8 programmed on Zone 2 and Central Police district 6 and 9. Also on Zone 2. Sometimes I listen to North fire on Zone 1 but it is programmed on a different system.

If you want to hear J band or sometimes called administrative band or emergency band the SEPTA UHF T police frequency simulcast J band.

An interesting note, on the far Northeast and Central Zone 2 site normal filter which is global works fine but on the North fire band which is Zone 1 site works better on wide normal. Who knows? I will say this. The SDS 100 picks up as well as the apx 7000 but of course it doesn't have the loud volume. Hope this helps.

 

[phillydjdan]

Bob is correct: Simulcast in this instance means several tower sites transmitting the same signal simultaneously. As for talkgroup simulcasting, PPD's J, T & M Bands are broadcast over both "sites" as well as North and South Fire and North and South Medic. I believe this is for interop purposes. The fire admins can monitor the citywide police chatter while affiliated with their own site, while the police admins can do the same with the fire channels.

 

[trentbob]

Hey Dan, nobody knows more about Philly's system than you do. Happy Father's Day to you, I'll be with my daughter too.

A quick note, that UHF frequency that was simulcasting that agency north of Philly threw the switch again and is off... apparently they had forgotten and left the switch on after that multi-state Pursuit. Rats. Talk soon.

 

[CqDx]

Here are some background on Site 5 and Site 6 700MHz underground channels, below is an excerpt from public bid documents three years ago.

Pro96com shows Site 5 (774.91875) and Site 6 (774.49375) are both connected to 3B2 zone core.

 

[IAmSixNine]

To give another example of what they are talking about.
https://www.radioreference.com/apps/db/?sid=7349
Fort Worth regional radio system is set up in a similar way.
Fort Worth Police use one "layer" and Fort Worth Fire/EMS use another "layer"
Both layers act as different systems. Both agencies use the other as back up. SO if the layer with police go down they can go to their radios, go to their back up zone and use police channels on the Fire/EMS layer.
So on paper its one big system. But when monitoring its several best to program it up as several different systems based on what you want to monitor. Layer 1 and Layer 2 geographically over lap each other.