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Newb Trunking Question

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Dave_D

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162
Hi all,

While analyzing the locations (according to FCC licenses) of some systems in my area, I noticed something:

1.) Some trunked systems duplicate every system frequency at multiple towers.
2.) Other trunked systems distribute a subset of frequencies to one tower and the remaining frequencies to another tower.

While the first arrangement makes sense to me, I don't understand how a secondary tower can extend service without carrying the system's control channel. For example, if five frequencies are carried on Tower A (including the control channel) and a sixth frequency is carried on Tower B, how does one in range of only Tower B use the trunked system?

Thank you!

Dave
 

seamusg

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Feb 10, 2004
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Location
Grand Blanc, MI
Dave_D said:
Hi all,

While analyzing the locations (according to FCC licenses) of some systems in my area, I noticed something:

1.) Some trunked systems duplicate every system frequency at multiple towers.
2.) Other trunked systems distribute a subset of frequencies to one tower and the remaining frequencies to another tower.

While the first arrangement makes sense to me, I don't understand how a secondary tower can extend service without carrying the system's control channel. For example, if five frequencies are carried on Tower A (including the control channel) and a sixth frequency is carried on Tower B, how does one in range of only Tower B use the trunked system?

Thank you!

Dave
1. This is a simulcast system where all towers transmit the same on the same channels at the same time.
2. This is a smart zone system, where each site operates like a seperate system, except they are connected to a central point that controls them. Each site will have their own CC and channels can be reused between sites if they are far enough apart as not to cause trouble. A person on Tower B uses the CC for Tower B and if they need the traffic from Tower A the Main Controller will send that traffic to Tower B. On multi tower systems all towers are linked for both CC data and voice. Suggest you read the WIKI for trunked systems.
 

JohnnyGalaga

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seamusg said:
1. This is a simulcast system where all towers transmit the same on the same channels at the same time.
But wouldn't that cause the system to interfere with itself ? When 2 people key up at the same time on the same frequency, they interfere with each other so that you can't hear either one of them.

Certainly, having multiple repeaters at different towers all transmitting simultaneously on the same freqeuncy would be a mess..
 

loumaag

Silent Key - Aug 2014
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JohnnyGalaga said:
But wouldn't that cause the system to interfere with itself ? When 2 people key up at the same time on the same frequency, they interfere with each other so that you can't hear either one of them.

Certainly, having multiple repeaters at different towers all transmitting simultaneously on the same freqeuncy would be a mess..
No it would not. This is done all the time with both trunking and conventional systems. It is all a matter of timing.

Speaking of timing, it is time for you to do some research. :D
 

JohnnyGalaga

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So ho come when 2 hams key up at the same time, they interfere, but 2 repeaters at the same doesn't?
 

loumaag

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JohnnyGalaga said:
So ho come when 2 hams key up at the same time, they interfere, but 2 repeaters at the same doesn't?
Please don't confuse commercial systems designed to transmit on the same frequency with ham repeaters. Indeed, note that if two PD units key up at the same time you get that same effect. That does not have anything to do with fixed transmitters designed to transmit the same signal at the same time.

For this to work the frequency must be the same (like with in a Hz or 2), the audio phase must be controlled, and you should limit the overlap areas to as small as practical. Much beyond that simple explanation I will leave for you to search out on your own.
 
N

N_Jay

Guest
Think of Simulcast as "controlled Interference", much like Stereo and a hologram.

You create and control interference to accomplish a specific gaol.

You design the system SPECIFICALLY to control the interference that will be created by the system.

p.s. I charge between $150 and $200 an hour and a very small simulcast design will take about 80 to 160 hours, plus travel and expenses.

THEN you get to start buying equipment.

-------------------------------------------
The below was written first, then I decided to give a "real" answer first, but still though the below was important to the message
---------------------------------------
Lets see if I can sum up 22 years of engineering in a sentence.

Hmmmmm . . . . . . . .

Hmmmm . . . . . . .. .

Hmmmmm. . . . . .


I've got it.

. . . . .


. . . . .


. . . . . .

Go study!
 
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