This article first appeared in the October 2001 issue of Monitoring Times.


During last fall's contested presidential election, Palm Beach County in Florida was ground zero for the confusion and varied opinions of politics. Public safety radio systems in that county seem to be following the example of their election boards as yet another trunked radio system has been announced.

Palm Beach County is the largest county in Florida with a population of more than one million people and covers more than 2,500 square miles. A number of cities and towns in the county are part of the Municipal Public Safety Communications Consortium, Inc. (MPSCC), which in April selected a new public safety communications system for their members.


MPSCC selected a relatively new system called OpenSky from a company called M/A-COM based in Massachusetts. Under the terms of an 18 month, $8 million agreement, M/A-COM will provide base stations, mobile and handheld radios, and support services for a digital voice and data network that will link several dozen municipalities within the county.

OpenSky appeared on the public safety radio scene in 1998 when the Orange County Transportation Authority (OCTA) in California chose M/A-COM to provide a digital trunking system for about 450 buses and other vehicles used by the agency.

A year later the state of Pennsylvania, under a number of deadlines and no small amount of lobbying, chose to implement a statewide communications network using the M/A-COM OpenSky system. This is by far the largest OpenSky network ever to be built, covering more than 45,000 square miles and supporting well over 25,000 users. Seven regional operating centers will link 250 radio tower sites to provide voice and data connectivity for more than 20 state agencies.

Last year the Pennsylvania counties of Cumberland (in August) and Lancaster (in December) voted to deploy OpenSky networks for their own local radio communication needs. Other counties are in the process of testing the system for suitability in their localities.

OpenSky Protocol

OpenSky radios operate within the FCC frequency allocations for trunked operations, with the normal 25 kHz channel spacing. Radios receive on frequencies between 851 MHz and 870 MHz and in normal operation transmit between 806 MHz and 824 MHz. When the radio is operating in talk-around mode (direct radio-to-radio, without a repeater), it can transmit on any channel between 851 MHz and 870 MHz.

OpenSky divides the 25 kHz radio channel into two time slots. This time division multiple access (TDMA) method allows two simultaneous conversations to share one radio frequency channel. Since all transmissions are fully digital, OpenSky can carry both digitized voice and data traffic over the same link. Each conversation can be either digitized voice or a raw data link operating at 19,200 bits per second.

Voice traffic is compressed and encoded using the Advanced MultiBand Excitation (AMBE) from Digital Voice Systems, Inc., the same company that licenses the Improved MultiBand Excitation (IMBE) vocoder for APCO-25 radio systems.

Older analog radios will work with the new system, since OpenSky radios and base stations are able to operate in conventional analog FM mode with sub-audible tone squelch.

Internet Protocol

One of the biggest selling points for OpenSky is that their network is based on the IP (Internet Protocol) standards originally designed for the ARPANET (Advanced Research Projects Agency Network), the same standards now in widespread use in the Internet. Such an IP-based network allows the use of more common, less expensive infrastructure equipment and computer software.

Each OpenSky radio is an IP "node" in the network, with it's own unique address. By using the Internet standard Transmission Control Protocol (TCP), end-to-end connections are available to each mobile user. OpenSky radios typically have an RS-232 serial interface, which provides a 19,200 bit-per-second data connection to a laptop or other external device. This provides the capability of using common Internet applications on mobile computers without a lot of additional investment.

Since most operations inside the radios are performed by software, programming can be done "over the air." Frequencies, talkgroups, and even the firmware that controls the radio can be changed and updated over the radio link. Base stations and radios also include on-line maintenance capabilities, allowing them to be checked and updated remotely from a network management center.

On the ground, all voice and data traffic is routed using IP. Voice messages are compressed and delivered using Voice over IP (VoIP) technology.

OpenSky and EDACS

Interestingly, OpenSky and EDACS (Enhanced Digital Access Communications System) are now owned by the same parent company.

Once upon a time, General Electric had an operation in Lynchburg, Virginia, which included a radio systems division. They were perpetually number two in sales behind Motorola. Ericsson bought the operation in 1989, but sales of public safety radio systems continued to lag.

In January of 2000, Ericsson sold the Private Radio Systems division to a Pittsburgh, Pennsylvania-based company called Com-Net, but retained 20 percent ownership. The new Com-Net Ericsson Critical Radio Systems continued to sell and maintain EDACS radio systems.

During this period, Com-Net Ericsson was awarded the contract for the Florida Statewide Law Enforcement Radio System. Motorola had won the contract, at the time the largest contract in land mobile radio history, and began installation in 1988, but in 12 years had spent $110 million and was only 40 percent complete. A number of factors complicated the situation, but in the end a less expensive proposal to complete and maintain the system was awarded to Com-Net.

In April of this year Tyco International bought Com-Net Ericsson Critical Radio Systems and placed it under M/A-COM, which is part of Tyco Electronics in Harrisburg, Pennsylvania. This is the same M/A-COM that sells OmniSky systems.

Although M/A-COM is hoping that marketing and contracts experience from Com-Net Ericsson will help promote OpenSky products, existing EDACS and ProVoice (the follow-on to EDACS) systems continue to be sold.

Clarksville, Tennessee

The city of Clarksville, Tennessee, northwest of Nashville near the Kentucky border, will spend more than $3 million to replace their conventional 450 MHz radios with a new three-site, eight channel 800 MHz ProVoice system from M/A-COM. Initially the police department will take delivery of about 500 radios, with another 200 to be spread among the fire department's 10 stations. Public works and other city services will eventually migrate to the system.

Shelby County, in southwestern Tennessee, and the Saturn automobile assembly plant in Spring Hill have both used EDACS radio systems for many years.

Oklahoma City, Oklahoma

In July of this year, the Oklahoma City Council approved M/A-COM as the preferred supplier of the city's new EDACS network, which will ultimately include all of the city departments.

Palm Beach County, Florida

Hi Dan:

Saw your article in the August issue of Monitoring Times about Palm Beach County, FL and thought I'd give you an update.

The Palm Beach County system is a Motorola SmartZone APCO-25 (IMBE) Astro/analog system with 4 cells:

Cell 1 = Palm Beach County with 28 frequencies (not 26) at 10 sites
Cell 2 = Boca Raton with 10 frequencies at 1 site
Cell 3 = Boynton Beach with 5 frequencies at 1 site
Cell 4 = Delray Beach with 5 frequencies at 1 site

Cells 2, 3, and 4 are using IMBE digital full time for Police and Fire, while Public Works is all analog. The control channel is the 3600 baud version, thus the Trunk Trackers will track it. On ALL SmartZone cells, talkgroups 16 to 8176 (Hex 001 to 1FF) are IMBE digital, while 8192 to 65520 (Hex 200 to FFF) are analog. On the county Cell (#1), 21 of the 28 transmitters are analog-only, while the remaining 7 transmitters are dual-mode (i.e. capable of both analog and IMBE digital). Palm Beach County will run all analog except OCB, SRT, and TAC units.

The County's VHF system is NOT completely gone yet - they are simulcasting between the trunked and VHF system, so either radio can be used for now. Eventually they will remove the simulcast.

County Fire-Rescue still must purchase their radio equipment and will not switchover until at least next year, then after that all Local Government (who is currently on lowband) will be switched.

Currently there is no way for Palm Beach County to talk to Martin and Miami-Dade County other than through the NPSPAC channels. Martin County uses an EF Johnson LTR Multi-Net 2 trunked system, while Miami-Dade uses an EDACS trunked system. There are currently no patch capabilities between the Palm Beach County system and Martin and Miami-Dade Counties, but a patch to Martin's system is planned, as well as a patch to the conventional systems of Hendry, Glades, and Okechobee Counties. Broward County uses a Motorola system so it is simply a matter of entering their system into the Palm Beach County radios, although currently no Palm Beach Sheriffs Office radios have ANY Broward talkgroups in them now, only future-use talkgroups for patching to Broward. Boca is the only agency with Broward talkgroups programmed into them. Also, NONE of the agencies on this system have any state talkgroups in them.


Analog: 856.3375, 857.3125, 857.3375, 858.3375, 859.3125, 859.3375, 860.3375, 866.1000, 866.1250, 866.3250, 866.3500, 866.6000, 866.6250, 866.7500, 866.8250, 867.1000, 867.3250

Control: 867.3750, 867.5750, 867.7625, 868.7250

Digital: 856.3125, 858.3125, 860.3125, 868.2250, 868.3750, 868.6500, 868.7000

Three additional frequencies are licensed but not in use: 866.850, 867.350, 867.400.

Simulcast talkgroups:

26704 CH 1 - 154.845 Dispatch District 3 North
26768 CH 2 - 154.725 Dispatch District 1 Central
26928 CH 3 - 154.815 Dispatch District 5 West
26832 CH 4 - 154.785 Dispatch District 4 South
27216 CH 5 - 154.650 Inquiry 1

NOTE: All frequencies in Cells 2, 3, and 4 are dual-mode digital and analog capable.


Analog: 852.5625, 852.5875, 852.6125, 853.6375, 853.6625, 853.7875

Control: 853.8125, 854.5875, 854.6625, 854.6875


Analog: 856.2875

Control: 857.2875, 858.2875, 859.2875, 860.2875


Analog: 866.3750

Control: 866.7750, 867.0750, 867.6750, 868.1500

The talkgroup layout is pretty clear, except for inter-agency communications. None of the inter-agency talkgroups are in the same channel location between all of the agencies (like Broward County with "System 14"). For example, if a Delray Police unit wanted to talk to a Palm Beach Sheriffs Office unit on Global Common 1 (talkgroup 64016 decimal, FA1 hex), the Delray unit would switch to Zone C, channel 13; but the Palm Beach Sheriffs Office unit would switch to Zone 8, channel 7. Another example, Boca Raton and Delray Beach both have the 5 "Metro" talkgroups, but Palm Beach Sheriffs Office and Boynton do not.


State of Michigan

Just to let you know I enjoy your column. And just to give you a little information on the State Police radio system. Phase 3 will be taken over by the State Police radio technicians on August 24 and installation of phase 4 will start with pre-work September 1. Installation starts in the Upper Peninsula on October 1 and with mild weather will finish the 80 tower sites by January 1. By the way, there is talk that the data link will not be installed.


That's all for this month. More information is available on my website at, including information on manual updates for the Bearcat 245XLT. As always, I welcome your electronic mail sent to dan @ Until next month, happy monitoring!

Comments to Dan Veeneman

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