Open Sky simplex question?

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jrm5265
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Joined: Sat Dec 13, 2003 6:13 pm
Location: Covington Ga

Open Sky simplex question?

Post by jrm5265 » Thu Sep 21, 2006 8:07 am

our county is in progress of installing an Open Sky 800 system our narcotics unit needed simplex channels in our radios and we were told we cant have that. They told us that we would have a "little box" that we would take with us and it would enable them units to do "simplex" ? I asked if it was a mobile repeater and they said NO its a device that will let them talk simplex its not a repeater can somebody explain this to me? Thanks

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Meatball
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Post by Meatball » Thu Sep 21, 2006 9:01 pm

I haven't had any chance to really play with Open Sky equipment so I'm going to have to guess a bit here.

I have worked with EDACS systems before and they have something they call a "SCAT" site (Single Channel Autonomous Trunking). The SCAT site acts as a control channel and working channel all in one. It acts as a control channel, and once the call is placed, it then switches to functioning as a working channel for the duration of the transmission. The radio "thinks" it's on a full-fledged EDACS system.

I'm guessing the "little black box" is something similar. It probably contains a low power transmitter, receiver, and digital control circuitry. Open Sky is a 4-slot TDMA system, and works similarly to the older TDMA cell-phones. Each talkgroup is assigned a time slot on a single RF channel. I would guess that your box is a low-power mini TDMA system that's used to "fill in" where there's no coverage from the main site.

It's "sort-of" a repeater, but it also contains all the digital processing and signalling hardware and software.

You could certainly program an EDACS radio to have a system of conventional simplex channels, but since the Open Sky system is more like a cellphone than an analog radio, simplex channels are not an option. I think the omission of simplex capability is probably more one of cost/hardware simplicity/engineering; there's certainly no problem with digital simplex channels on P25 radios (but, conventional P25 is still FDMA). MACOM probably didn't want to bother trying to engineer the ability to do digital simplex into the terminals (it would be pretty messy, and it would take up RAM and hardware that they need to devote to the main mode of operation).

That's my educated guess, anyway. Maybe somebody else who is more familiar with Open Sky than I am can elaborate.

jrm5265
Posts: 23
Joined: Sat Dec 13, 2003 6:13 pm
Location: Covington Ga

ok

Post by jrm5265 » Fri Sep 22, 2006 6:46 am

thanks for that info man, I guess our unit and SWAT are the only ones that will be using the system that will have a need for occasional simplex and thats probably the case in all of these type scenarios
Thanks

nhiester
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Joined: Wed Jul 05, 2006 6:37 pm

Post by nhiester » Fri Sep 22, 2006 9:56 am

If you are using the P800 or P801 portable, they will do Analog conventional and P25 conventional along with Open Sky. The P7200IP can do many more formats.

My guess is that the Black box is a VTAC repeater system. It may be a policy issue that is not allowing conventionals, but it is not an equipment issue.

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