LASO and simulcast
- Thread starter osxscan
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Yes they do. For example, when I listen to Lakewood/Cerritos Dispatch 14, if things are fairly busy in the area, they will broadcast only this area. When things slow down, for example, late at night, early in morning, I often hear stuff from Disp 15 (Lancaster/Palmdale) and other areas. Also, during a robbery or other significant event, they will simulcast on several frequencies.
If you follow LASO frequencies around 483 Mhz on an SDR, you will see several channels go on simultaneously at these times. Its the same transmission. Whether LASO has any specific standards for when they do this, I don't know, but it is quite common.
If you follow LASO frequencies around 483 Mhz on an SDR, you will see several channels go on simultaneously at these times. Its the same transmission. Whether LASO has any specific standards for when they do this, I don't know, but it is quite common.
Aero125
Member
LASD repeater system has "voting" receivers so the best signal received by whichever tower wins. There are repeaters throughout the county and coverage varies depending on which one you are hearing at any given transmission, but obviously the one with the best coverage near a station area would be most active for them.
scottyhetzel
Member
It's not a vote system,, each station area has a local mountain antenna along with its L Tac antenna on the local station... Freq like seb or air/k9 are simulcast/multicast co. Wide. Go to the database and pick a call sign and see the antenna locations....
LASD uses simulcast on all it's dispatch channels from two or more sites per frequency. In addition to transmit sites additional receive-only sites also add to the area of coverage on the input side.
For example Dispatch 8 Industry utilizes three transmit sites: Rio Hondo, Johnstone, and San Pedro Hill plus two additional receive-only site: Puente Hills Nike and Kellogg Hill area.
The harder to cover areas often have more simulcast sites such as Dispatch 7 which needs three sites just to cover Catalina Island and then a couple more on the mainland for Lomita/PV.
The station UHF antennas are for fallback purposes only in case of disruption to the mountaintop system occurs. The audio heard at stations is the same voted radio traffic heard up at SCC. It is received at the stations via microwave link.
For example Dispatch 8 Industry utilizes three transmit sites: Rio Hondo, Johnstone, and San Pedro Hill plus two additional receive-only site: Puente Hills Nike and Kellogg Hill area.
The harder to cover areas often have more simulcast sites such as Dispatch 7 which needs three sites just to cover Catalina Island and then a couple more on the mainland for Lomita/PV.
The station UHF antennas are for fallback purposes only in case of disruption to the mountaintop system occurs. The audio heard at stations is the same voted radio traffic heard up at SCC. It is received at the stations via microwave link.
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scottyhetzel
Member
Paul,
Why would San Pedro tx, kinda far??? Where does temple station transmit from other than rio Hondo?
I thought the desk tx from the station to local
Why would San Pedro tx, kinda far??? Where does temple station transmit from other than rio Hondo?
I thought the desk tx from the station to local
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Aero125
Member
Thank you Paul for expanding on the LASD receiver voted system and simulcast system LA County has such terrain and obstruction challenges the only way for their radios to work is with those features, even within 1 dispatch channels coverage area. Some Dispatch and LTAC channels are shared between multiple stations with obvious single tower limitations to further illustrate the system needs. One example is Crescenta Valley/Altadena shares LTAC 8 with Santa Clarita.
From just south of Rowland Heights east of Fullerton road is a secondary site that Temple can use.
They do have a full base/repeater at the station on the Main and L-Tac frequencies for back up, "self Dispatch".
The receivers know what transmitter to use, so a radio in La Crescenta would bring up the local transmitter, and not Santa Clarita's tx.
SRC has a rather unique system in that channels are auto assigned based on dispatcher load/availability.
So if a unit keys up somewhere the channel automatically links up to a free dispatcher who handles the call. This is how you get multiple channels being handled by one dispatcher at a time.
If 10-33 traffic or something comes up the dispatcher can lock out all other traffic sending it to other "Free" dispatchers in order to handle the priority traffic.
This way traffic is almost always "Handled" immediately by someone.
It also is part of the reason for the busy tone so frequency 13 knows traffic may be occurring on frequency 12 in Lakewood which they don't know about.
So if a unit keys up somewhere the channel automatically links up to a free dispatcher who handles the call. This is how you get multiple channels being handled by one dispatcher at a time.
If 10-33 traffic or something comes up the dispatcher can lock out all other traffic sending it to other "Free" dispatchers in order to handle the priority traffic.
This way traffic is almost always "Handled" immediately by someone.
It also is part of the reason for the busy tone so frequency 13 knows traffic may be occurring on frequency 12 in Lakewood which they don't know about.
Last I heard they were going with the new system. But then again comments here and around seem to indicate the system may not be going so I don't know current status.
Did some interesting reading about that back a bit. Going to keep same system only on digital if it goes ahead. Not sure if they are keeping their 480 freqs for it or not. Can't remember. May be mixed freq too but again can't remember specifics. There is a thread in here with site info from a while back that lists frequencies used or someone can chip in.
Did some interesting reading about that back a bit. Going to keep same system only on digital if it goes ahead. Not sure if they are keeping their 480 freqs for it or not. Can't remember. May be mixed freq too but again can't remember specifics. There is a thread in here with site info from a while back that lists frequencies used or someone can chip in.
I'd sure like to see who floated that balloon.
Aero125
Member
LASD plans to be part of the LA-RICS system if it ever gets implemented. There is currently testing going on and an active forum thread about it for more information.
hpycmpr
Member
LA RICS is composed of two systems, voice and data.
The data system is cellular in concept and at low elevations. The data system is having problems with site locations.
The voice system is at high elevations, ie mountain tops.The voice system is proceeding well as far as I know.
Steve
The data system is cellular in concept and at low elevations. The data system is having problems with site locations.
The voice system is at high elevations, ie mountain tops.The voice system is proceeding well as far as I know.
Steve
On Industry dispatch, San Pdro Hill provides coverage for the backside of the hill (La Habra Hts)
From what I remember Temple is also simulcasting from Mt Disappointment which is up near Mt Wilson with receive-only from SCC. There may be another site I'm not remembering right now.This info is about ten yrs old but change comes real slow at LASD.
You can't go by the FCC license because the radio shop at ISD has licensed each site for every LASD frequency weather its being used or not.
Despite what the license says a tech told me that the transmitters are putting out on average about 40 watts, which helps with wear and tear. I think the lower output also assists in the simulcast phasing.
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If for example Crescent Valley and Altadena needed to both do self-dispatch CV might use Disp 1 and Altadena L-Tac. If this were the case Altsdena desk would be heard simulcast in the full coverage area of L-Tac including off Bald Mtn up near Gorman.
The system is not set up to select single transmit sites.
The only time stations would their station antennas for this is if SCC went down and access to mountain-tiop transmitters were also down.
There are many stations that could not reach much of their patrol areas from the station antenna. It is just a resource of last resort.
Back when there was a big argument over the busy tone being incorporated into the new system I found some documents which made fascinating if exhausting reading.
LASO custom ordered an extremely detailed spec'd system for themselves. It was astounding the amount of specific details involved on everything you could imagine and a heck of a lot you probably couldn't.
How high a chair would be, the placement of buttons, the length of the mic cord, capabilities for this and that to the nth degree etc.
The busy tone, full duplex operation and "The Patch" were integral components of the requirements.
With that said God knows if anything has been changed in the intervening time frame since I saw that document. You know how that goes. LOL
Don't know if they still do this but back when they used to periodically have the station take over dispatch comms for a period. (Shift I think) This was for emergency comms practice.
Each station could dispatch themselves in the event of comms failure on a county wide or localized basis. I believe it was for earthquake damage preparedness but it may now encompass any comms failure situation.
I remember every so often it would happen and you'd hear all comms go out from the local station. I seem to remember LACoFD having something similar but don't quote me on it. Its been a long time.
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