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Monroe County Simulcast

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Dec 28, 2005
Martin, Ohio
I'm a little confused about simulcast systems and CQPSK modulation. I live in western Ottawa County in Ohio, which is about 20 miles south of Toledo. I can pick up the Monroe County system but it cuts in and out quite a bit. But I am able to pick up the Flat Rock tower from the MPSCS with almost perfect reception. So my question is what is the advantage to using the CQPSK modulation on a simulcast system? The Ohio MARCS system uses a simulcast system in Franklin County without CQPSK and so does Delaware county in Ohio and the reception is much better. And what does CQPSK stand for?


Global Database Administrator
Dec 23, 2001
Ann Arbor, Michigan
CQPSK stands for [SIZE=-1] "Compatible (Differential) Quadrature Phase-Shift Keying"modulation. This allows two or more towers to transmit the same signal off all towers at the same time. Such is the case with the Monroe County TRS.

"Project 25 (P-25) systems utilize digital modulation techniques to transmit the digital ones and zero’s across the air interface. These formats are defined in the TIA/EIA-102 standards and apply to Phase I P-25 systems and Phase II systems. Each of the modulation formats accomplishes the task of transmitting digital information over the air in a bandwidth efficient manner. Two modulation formats are called out in the P-25 standard, C4FM modulation in a 12.5 kHz bandwidth which is used for current P-25 Phase I systems and CQPSK or Compatible Quadrature Phase-Shift Keying modulation which is intended to be utilized for Phase II P-25 systems operating in a 6.25 kHz bandwidth."

"Phase 1 P-25 systems, utilize a form of digital modulation called C4FM. C4FM is a 4-carrier modulation format where the carrier is shifted in frequency at a particular rate (time) to a particular location around a center frequency. This allows for each of the 4 "states" to represent a binary number. Each state is a "DiBit" or "Symbol" which contains two bits of information." That said, the Flat Rock tower would be an excellent example of this format.

The future Lucas County Project 25 Simulcast TRS, will use CQPSK modulation.


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