Simulcasting

smithken

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More efficient use of frequencies. The simulcast system I monitor has 5 physical sites from what I can tell, I don't know what the minimum number of frequencies is per site but lets say each site has to have a control channel and a voice channel so 2 channels. 5 individual sites would therefore use 10 frequencies. If those same 5 sites are simulcast they would only need 2 frequencies since each site would use the same frequencies.
 

ofd8001

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It is usually seen in communities that have many large buildings like hospitals, warehouses, big box stores, shopping malls etc. The FCC doesn't want to approve big blowtorch transmitters of hundreds of watts to achieve the in-building penetration coverage. The high power means a frequency can't be re-used a couple of counties over, etc. Frequencies are in scant supply.

A number of lower power transmitters working together on same frequency (simulcasting) achieves the same level of coverage.

Before I retired from the fire service, our community went to a simulcast system. There was a day/night difference in improvement in what I could hear on the new system with my issued radios. Gave me heck trying to listen with a scanner, though.
 

n5ims

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It also allows a system to make better use of their antenna's down tilt to limit the system's signal to cover, as much as possible, only the minimum area necessary. Instead of blasting a very strong signal from a single transmitter over a very wide area, the simulcast sites can concentrate on the city boundaries (for example) to provide good handheld coverage there while minimizing coverage outside the city where little coverage is generally needed. This allows for those frequencies to be reused closer to that system without causing interference.
 

Ubbe

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There's hardly any simulcast systems outside of US and there's probably a reason to it. Several transmitters on the same frequency will always be more difficult to receive as they at some point will cancel out each others radiowaves and also the interference between them requires special radios, and scanners, to receive properly. Those who listen to simulcast systems will at occasions hear that patrols and users ask for a transmission to be repeated beacause they had a drop out of the signal.

In other countries they have the same amount of sites, which is needed to get full radio coverage, but each site use their own frequencies, if they have overlapping coverage. When one site doesn't have coverage the digital radio have measured the signal strenght from three other sites and instantly switch to the strongest one of them without the user noticing anything.

In a simulcast system all users are on the same frequency, which has a fixed amount of max users before it overloads and stops working. In non-simulcast systems the users are divided up to the different sites and will have a much higher capacity. That means that simulcast system have to use more channels to get the same capacity as non-simulcast system. So the advantage of more efficient use of frequencies are mostly lost due to the higher number of channels needed to accommodate all users. If there was a system with few users and few channels it would anyhow require another license for the additional coverage where FCC normally could have given the same frequency to another user, with another license fee, that where far away from the first users coverage. So simulcast have never been an option in other countries as it's no real advantage to use that system type.

/Ubbe
 

ofd8001

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I do wonder "if" somewhere in their thinking, this came in to it?
Nah, as easy and cheaply (ADP) that encryption can happen, I'm sure it wasn't intention. Particularly since in one place simulcast is bad but 100 yards away, it is pristine.

Even more interesting, our VHF analog paging system is a 5 site simulcast deal. Never heard of garble on that, once it was set up properly.
 

maus92

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There's hardly any simulcast systems outside of US and there's probably a reason to it. Several transmitters on the same frequency will always be more difficult to receive as they at some point will cancel out each others radiowaves and also the interference between them requires special radios, and scanners, to receive properly. Those who listen to simulcast systems will at occasions hear that patrols and users ask for a transmission to be repeated beacause they had a drop out of the signal.

In other countries they have the same amount of sites, which is needed to get full radio coverage, but each site use their own frequencies, if they have overlapping coverage. When one site doesn't have coverage the digital radio have measured the signal strenght from three other sites and instantly switch to the strongest one of them without the user noticing anything.

In a simulcast system all users are on the same frequency, which has a fixed amount of max users before it overloads and stops working. In non-simulcast systems the users are divided up to the different sites and will have a much higher capacity. That means that simulcast system have to use more channels to get the same capacity as non-simulcast system. So the advantage of more efficient use of frequencies are mostly lost due to the higher number of channels needed to accommodate all users. If there was a system with few users and few channels it would anyhow require another license for the additional coverage where FCC normally could have given the same frequency to another user, with another license fee, that where far away from the first users coverage. So simulcast have never been an option in other countries as it's no real advantage to use that system type.

/Ubbe
Public safety entities don't pay licensing fees to the FCC.
 

ofd8001

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Public safety entities don't pay licensing fees to the FCC.
While that's true, but for public safety entities the FCC requires that frequencies be "coordinated" so that there isn't overlap or other harmful interference. The frequency coordinators will charge fees for their services. So an initial license has a cost associated with it.

"Back in the day" our fire department was looking to get a repeater. We had to go to two different coordinators because we were trying to use a frequency assigned to a different service (I think it was game wardens). So that was an experience and expense.
 

maus92

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While that's true, but for public safety entities the FCC requires that frequencies be "coordinated" so that there isn't overlap or other harmful interference. The frequency coordinators will charge fees for their services. So an initial license has a cost associated with it.

"Back in the day" our fire department was looking to get a repeater. We had to go to two different coordinators because we were trying to use a frequency assigned to a different service (I think it was game wardens). So that was an experience and expense.
Yes, I realize that. There is administrativa that needs to be completed (like in any country) and there are costs to identify and secure channel resources which can be handled by private companies, consultants, industry associations, quasi governmental organizations, local governmental groups (RPCs,) etc. PS just doesn't pay a fee for the use of the spectrum.
 
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