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  #1 (permalink)  
Old 11-08-2012, 2:47 PM
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Default ARMER Simulcast Vs.Non-Simulcast Sites

I have focused on the Dakota County Simulcast site for so long, that I am just now starting to pay attention to other sites. I have noticed that some are not listed as simulcast. I understand that the prison sites are not simulcast and that makes sense. As far as other ones, for example it looks like Washington County is not a simulcast site. Does that make much difference to the end user listening on a scanner? I would think that a more rural county, like Pine County, would be simulcast, but according to the database it does not appear that it is.
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Old 11-08-2012, 6:45 PM
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To my knowledge, simulcast sites are done for two reasons: the need for better in-building coverage in larger/denser buildings and/or a shortage of 800Mhz pairs to use in areas that need more sites for coverage.

The majority of the outstate sites are not simulcast, but single or ASR sites (Area Site Repeater??).

For a scanner listener, simulcast sites are often a pain to listen to, especially if the sites are an equal distance away. The cheaper receivers in consumer scanners have a harder time sorting out the effects of multipath interference, where a signal from one site arrives slightly out of phase from that of another site, often canceling itself out. When this happens, your scanner may show full signal strength but have broken, garbled, or no audio.

-Dave
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Old 11-09-2012, 10:26 AM
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Quote:
Originally Posted by davef3138 View Post
. . . simulcast sites are often a pain to listen to, especially if the sites are an equal distance away. The cheaper receivers in consumer scanners have a harder time sorting out the effects of multipath interference, where a signal from one site arrives slightly out of phase from that of another site, often canceling itself out. When this happens, your scanner may show full signal strength but have broken, garbled, or no audio.

-Dave
Y'know, that's about as succinct of an explanation of the simulcast garble as I've ever seen! Good explanation!
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Old 11-09-2012, 3:29 PM
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All metro counties and Mnpls. are simulcast sites.

As you go outside of the metro some sites are simulcast and some are not it all depends on what type of coverage the system needs.

Yes simulcast is based upon certain needs as described which includes in building coverage as well as frequency re-usage.

It does suck to try and listen to a simulcast system if you are in between sites especially if both are passing traffic. I have been sitting and listening to a conversation and about half way through boom it gets really garbled or hard to hear, a little bit later it is ok. Why is this? Well tower A is passing traffic and not tower B but then someone affiliates to tower B. Boom now both towers are transmitting and the scanner is having a hard time with the two signals on the same freq. In essence since it is simulcast the radio should NOT know the difference but with digital it seems to have some issues.

On the flip side single sites suck because if you just have the one tower plugged in and nothing is affiliated to it you will not hear anything.

Happy scanning.
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Old 11-11-2012, 2:11 PM
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Cool Simulcast Vs Non Simulcast

Simulcast means one thing --ALL sites in a simulcast group transmit the SAME data at the SAME time and does not switch signals between sites of a simulcast group. (How does a Transmit site know what site a radio is listening too.- It can't) The receiving radio processes all the signals it receives, not like a scanner only one at a time.
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Old 11-11-2012, 11:04 PM
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To add to what amradioguy2 said, not only do all of the transmitters in the simulcast region transmit the exact same data/audio on matching frequencies, they also all receive as well.

One of the sites in a simulcast region is the called the "prime" site. It receives what all of its connected remote sites hear, and chooses the best signal to send back out for transmission and onto the microwave network to the rest of the system.


The client radios also "see" all of the simulcast sites as one "big" site. I don't believe there's a way for them to tell the site members apart.

-Dave
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Old 11-12-2012, 9:30 AM
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I only addressed the out bound operation.
A simulcast (site) is made up of --a Prime site ( does not need to be located with a RF site but is most often is colocated with a RF site. A RF site any number from 1 to 15 sites.

Site Controller - Which controls the the operation of the the simulcast site and talkes with the zone controller. The Zone controller only thinks of a simulcast group as 1 site now how many towers it controls.

Comparator - controls the rf sites in both tx and rx operation. during tx all rf sites on the same channel are tx at the same time and with the start of each tx message controls the the outbound timing of the simulcast signals. During RX operation the comparator looks at all the incoming signals at a packet by packet rate and selects the best data for sending to the MSO and for outbound signal.

GPS RX - One is needed at the prime site and at each RF site. Used for timing of simulcast signals and frequency reference at RF sites.

RF Site - 1 to 15 sites and has 2 to 30 channels. all operating in full duplex mode..All sites control channel are on the air at the same time with the same data. and any voice channel needed is also tx from all the sub sites at the same time with the same data.
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