Definition check: Simulcast

[RyanXTS]

What is the correct definition of Simulcast, as it applies to this situation?

1. Broadcasting Dispatch on both 800 and VHF using 4 800mhz sites and 1 VHF site.

-OR-

2. The system cannot be considered simulcast until the VHF is being transmitted from more than one location, i. e. the 4 locations the 800mhz towers are at.

 

[N_Jay]

What is the correct definition of Simulcast, as it applies to this situation?

1. Broadcasting Dispatch on both 800 and VHF using 4 800mhz sites and 1 VHF site.

-OR-

2. The system cannot be considered simulcast until the VHF is being transmitted from more than one location, i. e. the 4 locations the 800mhz towers are at.

Yes!

Simulcast (in the broadcast world, but used in the LMR world) is simultainously transmitting on two frequencies.

Also called "Simul-Select" from the console feature of the same name.
Also called patching, etc.

Simulcast (typical of the LMR world) (Also called Quasi-Syncronous Trasmission [UK/EU]) is teh "art" of transmitting on teh same frequency from multiple sites with overlapping coverage.
I say "art" because there is much that is required to make these systems operate properly. (It is not ART, it is SCIENCE, but try explaining that to some of those who believe they are the only holders of the proper "Black Magic").

 

[akardam]

Simulcast has classically meant you're broadcasting the same thing on one or more "channels", i.e. whether it's a talkgroup, or a conventional frequency, you could potentially hear the same thing on channel 2 and channel 4 on your radio.

Sometimes people talk about simulcasting as meaning transmitting from multiple different repeater sites at once. I personally think that's kind of silly, because for example with a trunked radio system, you *are* transmitting the same audio on the same frequency at multiple sites. This, under normal circumstances, does not a simulcast make.

So I would say that definition #1 is the more commonly used definition (regardless of how many sites there are), but both definitions are more or less correct. Again, when most people say simulcast, they think, I can hear the same thing on this talkground *and* this other talkgroup, or this conventional frequency, *and* this other conventional frequency, or some combination thereof.

 

[nmfire10]

The act of keying up two or more transmitters at the same time. That's all there is to it. It could be multiple frequencies, or they could be on the same frequency and syncronized.

 

[mlevin]

Gene Hughes' Police Call book mentions that Simulcast is the commonly used but wrong term, while Multicast is the correct term. I don't really care what you call it, but was wondering if this is true.

 

[EricCottrell]

Sometimes people talk about simulcasting as meaning transmitting from multiple different repeater sites at once. I personally think that's kind of silly, because for example with a trunked radio system, you *are* transmitting the same audio on the same frequency at multiple sites. This, under normal circumstances, does not a simulcast make.

Hello,

I do not consider separate sites like in a Motorola Smartzone system as Simulcast. For trunking I think more along the line of definition 2. Zone (or Cell) five in the local Massachusetts State Motorola Smartzone system is a simulcast consisting of three sites (which may be unusual for a Smartzone system). I think the reason is the three sites were the original MDC type I system and it was expanded into a Smartzone system. Up until the recent conversion to Type II, the remaining type I radios used by MWRA and MDC could only use these three sites in Zone 5.

73 Eric

 

[N_Jay]

We can argue this ALL DAY, as there is NO standard definition of SIMULCAST.

It is a created word derived from "Simultaneous Broadcast".

Apply it as you see fit.

In the broadcast world, you will be assumed to mean transmitting on two or more broadcast media simultaneously. E.G. TV and FM

In the LMR world, you will be assumed to mean transmitting on the SAME frequency from more than one site. (Typically with overlapping coverage)

 

[CCHLLM]

Going by the definitions given in the manuals and the comm schools and manufacturers seminars and technical schools I have dealt with for over 35 years, the LMR world defines simulcast to be any system normally transmitting the same intelligence over two or more transmitters on the same frequency through a frequency managing system, hence the terminolgy "simulcast system". Multicast is described as broadcasting the same intelligence over more than one frequency or talkgroup by operator selection or by function. That terminology coincides with the markings on the control consoles and in the touch screen software that indicate system functions and controls.

Here's a look at one manufacturer's software programming tags. Under Simulcast functions for each simulcast channel we find:
"Simulcast>Normal/Disable toggle"
"if Disable>Site Select>Setup Enable>Default Site(s) Select>Add-Delete+Site Number toggle"

There is no provision for multiple frequencies or talkgroups in the Simulcast function as far as operator definition goes, only the ability to place a site in or out of normal operation on that frequency.

Under Multicast functions we find:
"Multicast Operator Select>Add-Delete+Channel or Talkgroup toggle"
"Multicast Default Channel>Add-Delete+Channel or Talkgroup toggle"
"Multicast Default Channel Defeat>Operator/Supervisor toggle"
"if Operator>Normal/Defeat toggle"
"if Supervisor>Supervisor Console+Password>Normal/Defeat toggle"

The operator can select and unselect channels and talkgroups at will to be controlled by the main TX button or pedal as the need arises, while another procedure is required to defeat Default channels and talkgroups.

A "default channel or talkgroup" is one that is not a part of the primary control system that is tied to a particular trunked talkgroup. An example would be a trunked system that has a conventional (VHF/UHF/800,etc) channel that repeats all the traffic on a specific talkgroup over the conventional channel for paging/dispatch purposes. It functions each time the particular talkgroup it's tied to functions and will do so unless its function is defeated at the control point. Another example would be a US Gov UHF trunked talkgroup tied to a municipal 800 trunked talkgroup. Each of those would consider the other to be the secondary. There are cases where the conventional channel is the primary and the trunked channel is the default or secondary, BTW.

Judging from all this, the LMR industry considers "Simulcast" as a function of the multi-transmitter coordinating "system", while multiple frequency and talkgroup broadcasts are considered a "Multicast" function.
Hope this helps flocculate the muddy waters.

 

[nmfire10]

Which leads to the question I ask people when they say there is simulcasting... "Is it simulcast, or simulcast.

 

[N_Jay]

Which leads to the question I ask people when they say there is simulcasting... "Is it simulcast, or simulcast.

???

I Don't know? Most people I talk to don't speak in italics. :wink:

 

[INDY72]

OK and here is a question: Is there such a function as a simulcast of a multicast operation?

 

[N_Jay]

OK and here is a question: Is there such a function as a simulcast of a multicast operation?

Sure. Of course it depends on YOUR deffinition of SIMULCAST and MULTICAST!

Lets say I have a UHF conventional channel which is made up of 3 sites SIMULCASTED (Using the Common LMR Meeting),
Then from the console (or any other apropriate means) I patch that to my VHF system.

I am simulcasting and multi-casting!

Or better yet, I have a channel Simulcasted in the urban area for better coverage, then I have teh same "Channel" (Traffic wise) multicasted on different frequencies in the rural area (due to site separation isssues, or lack of microwave, etc.)

Yep, doing it again!

 

[scanfan03]

I always thought that Simulcast was between 2 channels, and Multicast was between 3 or more channels. Hence the pre fix Sim and Multi. I don't know what Sim means, but I know that Multi means 2 or more. Or Multicast was between two or more different systems.

 

[northzone]

As far as Land Mobile Radio there is only one correct answer here and that is what WX4CBH stated in his first paragraph above.

Simulcast means transmitting the same information (voice or data) from more than one transmitter ON THE SAME FREQUENCY at the same time. Anything else, such as 800 and VHF or the same band on different frequencies is multicast.

 

[TXFirefighter112]

I always thought simulcast was using a pole in both hands while fishing....

J/K of course. Although I didnt have the slightest clue as to the real definition...

:lol:

 

[N_Jay]

As far as Land Mobile Radio there is only one correct answer here and that is what WX4CBH stated in his first paragraph above.

. . . .

Hey what was wrong with my answer? :wink: :wink:

 

[CCHLLM]

Nuttin' as far as I can see, worked for me.

 

[INDY72]

Multi=Multiple
Simul=At the same time.

From thier origins in greek.

To thier ends in GEEK...
MULTI+Cast: Multiple broadcasts, usually at the same time, consisiting of iether a common feed, or various feeds, through various forms of media.
SIMUL+Cast: Simultaneous broadcasting of a common feed, usually on a common media.

Examples-

PD dispatches on VHF Hi Band for Patrol, while also talking to Highway Patrol on VHF Lo Band. - Multicast -

PD is using both 155.6175 MHz, and 155.4300 MHz simultaneously to broadcast the same dispatch messages for all its units. - Simulcast -

Trunking version-

Site A is used for City PD, and FD Taciticals... whilst dispatches on Site B. -Multicast-

In County X there is a six site system, Sites D, E, & F, are used by the SO, and all 3 sites broadcast all the TG's in use by the SO at the same time.... -Simulcast-

Then there are the variations thereof. If you wanted to get confusing, you could say that patches of other agencies dispath (etc) are simultaneous multicasts when in use. This is especially common in dealing with trunked systems that are used by various EMS, and hospitals.... thus the infamous MED Patches, which may be simple multicast patched MED freqs, or simulcast vias multiple sites. Its all up to the system controllers how they want to set it all up, and up to dispatchers as to how they run each individual incident.

 

[N_Jay]

Multi=Multiple
Simul=At the same time.

From thier origins in greek.

To thier ends in GEEK...
MULTI+Cast: Multiple broadcasts, usually at the same time, consisiting of iether a common feed, or various feeds, through various forms of media.
SIMUL+Cast: Simultaneous broadcasting of a common feed, usually on a common media.

Examples-

PD dispatches on VHF Hi Band for Patrol, while also talking to Highway Patrol on VHF Lo Band. - Multicast -

WRONG

PD is using both 155.6175 MHz, and 155.4300 MHz simultaneously to broadcast the same dispatch messages for all its units. - Simulcast -

WRONG

Trunking version-

. . . . WRONG

. . . . .

You are just confusing the issue.

No-one was this carefull when they picked the terms.

and multi-cast on LMR is about the same thing as Simulcast in broadcast, so that kind of blows away much logic.

 

[rescue161]

In the trunking world, a great example of simulcasting is on the Federal SMR in Washington, DC. There are several sites (all trunking), but all using the EXACT SAME FREQUENCIES.

A great example of multicasting is the SC SCANA system (Spartanburg for sure - only part I've monitored). Transmitting the SAME data through different sites on DIFFERENT frequencies.

Simulcasting isn't used very much in the trunking world due to timing issues. It's just easier to use multicasting, like in a Smartzone system like SCANA. There is a LOT of setup time and maintenance time that goes into keeping all of the sites coordinated with each other when using simulcasting.

If you've ever heard a true simulcast system and heard the "lag"(if the timing is off), it'd be easy to understand why they steer away from these systems.

Another good example of the "lag" is when talking on a DSN line (for all of you military types)...