This article first appeared in the November 2003 issue of Monitoring Times.


Despite all the silence you hear while listening to police and fire department radio systems, the public safety spectrum in many locations is quite full. While efforts are underway to allocate new frequency bands, the Federal Communications Commission (FCC) has also been pushing to fit more users in the same amount of space. Their basic plan is to slice up the existing channels into smaller pieces and require users to operate within those pieces. This is a difficult requirement for the older analog radios, but the new digital systems -- including APCO Project 25 -- are prepared for this eventuality.

APCO-25 Modulation

The original APCO (Association of Public-Safety Communications Officials) Project 25 specifications, now a decade old, spelled out two phases for radio operation. Phase I operates in channels that are 12.5 kHz wide, which is the current FCC requirement. However, because the FCC wants to pack more users into the limited spectrum available, they'd like to eventually have everyone using radio channels that are 6.25 kHz wide, or half as much as before. To meet this requirement, Project 25 defined Phase II to operate within 6.25 kHz wide channels.

APCO-25 uses a modulation process called QPSK-c, which stands for Quadrature Phase Shift Keying, continuous. Modulation is just a fancy word for the process of carrying information content over some kind of carrier signal. The transmitter superimposes the information onto the carrier, and the receiver removes the carrier and reproduces the information. Everyday AM (Amplitude Modulation) and FM (Frequency Modulation) radios tune to a carrier signal and retrieve the audio information sent by the radio station.

For Phase I systems, the version of QPSK-c used is called Compatible 4-Level Frequency Modulation (C4FM). When the basic Project 25 specifications were being worked out a decade ago, C4FM was chosen primarily because it provides relatively good efficiency without requiring equipment manufacturers to produce complex and expensive radios. C4FM is designed to operate within a radio channel that is 12.5 kHz wide.

Under the Phase II plan of Project 25, another type of QPSK-c modulation called CQPSK (Compatible Quadrature Phase Shift Keying) is used. It's not all that different from C4FM, but requires a different transmitter and a little more work on the receive side to make things function correctly. The advantage is that it takes up less bandwidth than C4FM, allowing two users to fit where only one did before.

Because C4FM and CQPSK are so similar, the intent was that same basic receiver hardware could properly handle both Phase I (12.5 kHz) and Phase II (6.25 kHz) channels. This means that with modern digital signal processing (DSP) technology, the same scanner hardware should be able to handle both types of modulation.

Digital Simulcasting

As the new APCO-25 scanners make their way into hobbyist's hands, there are reports that they don't work correctly while monitoring some simulcast systems. (Simulcast just means that the same information is transmitted from more than one repeater at the same time, allowing users across a wide geographic area to all hear the same messages.) The symptoms are mainly the inability hear an entire transmission. The first second or two of voice is heard, which then trails off to silence.

To add to your list of acronyms, there is another type of modulation scheme that's used with some multi-site Project 25 systems. Linear Simulcast Modulation (LSM) is a trademarked term for a form of CQPSK that provides a way for receivers to properly handle multiple identical transmissions. It's just different enough that the regular C4FM processing doesn't work correctly.

Because no Phase II systems are currently in operation, the developers at Uniden and GRE didn't expect an immediate need to handle this type of modulation. However, several municipalities are using LSM/CQPSK modulation for simulcast, including Phoenix and Mesa in Arizona; the greater Twin Cities area of Minnesota; Hamilton County in southwest Ohio; and Austin and Travis County in Texas.

If you live near any of these areas, or monitor systems that are "pure" APCO-25 with simulcasting, you may want to wait until Radio Shack has an upgrade for the PRO-96.

As described in the August Tracking the Trunks column, the Radio Shack PRO-96 (built by GRE) was designed to accept updates to the "DSP Application" portion of the scanner through the use of flash upgrades. This kind of flexibility allows production problems and bugs to be corrected without the need to buy a new scanner or replace circuit boards. In this case, an upgrade can also add new features and capabilities.

Radio Shack is expected to provide a firmware update that will give the scanner the ability to process LSM transmissions. As of this writing there's no release date for such an update, or whether there will be a cost involved. There may be a way to have the upgrade done at your local Radio Shack store, or to download the upgrade from Radio Shack's web site. We'll keep you posted as we get more details.

No word yet from Uniden on a fix for their scanners, although they have a new pair of scanners in the works to compete with the PRO-96.

New Uniden Scanner

There's a rule of thumb in the software business: "Never buy revision 1.0," meaning don't buy a product when it's first produced, since it's likely to have bugs. It takes time to iron out bugs and integrate new features. This happened to the Pontiac Fiero in the 1980's, which was famous for production problems early in its life. On the other hand, if no one ever bought revision 1.0 there would never be revision 1.1.

In any case, Uniden is circulating pre-release information about a pair of enhanced scanners to correct some of the shortcomings of the current 250D and 785D digital scanners. The new 296D (handheld) and 796D (base/mobile) scanners are very similar to the 250D and 785D, but will have the ability to track digital trunked systems that use a 9600-baud control channel. Also, a digital decoder card will be included -- current scanners require the purchase of a separate card (the BCi25D) in order to handle APCO-25 systems.

So far there is no exact release date, although it's expected to be available in early 2004. Price is rumored to be around a thousand dollars, although no official list price has been forthcoming.

Rapides Parish, Louisiana

Dear Dan,

In the July 2003 Tracking the Trunks column you requested Talk Group IDs for Rapides Parish, Louisiana. This is a Motorola Type II system using frequencies 855.7125; 855.9625; 856.7125; 856.9375; 857.7125; 857.9375; 858.2625; 858.7125; 858.9375; 859.2625; 859.7125; 859.9375; 860.2625; 860.7125; and 860.9375 MHz.

All Talk Group Identifiers for the parish changed early in 2003; thus I've had some homework to do. (Thank you for motivating me to finally learn the ID Scan List feature on my scanners. Monitoring this way is a whole lot easier.) Here is a list of some of the more frequent IDs:

Rapides Parish Sheriff's Office

15344 Sheriff - Dispatch

15376 Sheriff - Tac 1

15400 Sheriff - Tactical

15472 Dept. of Corrections

15536 Dept. of Corrections

15568 Dept. of Corrections

15632 Sheriff - Tac 2




16432 Comm Interagency

City of Alexandria Police

15856 Police "A"

15888 Dispatch

15920 Dispatch 2

15952 Police "2"

City of Pineville

12272 Police

12304 Dispatch 2

City of Ball

2320 Comm Center

2384 Tac

2416 Fire Department

City of Lecompte

2640 Police

2672 Tac

2704 Fire Department

City of Woodworth

3184 Comm Center

City of Cheneyville

9744 Comm Center

England Air Park

13296 Security

13360 Grounds

Parish Fire/Rescue

3856 Comm Center Fire District # 2

12432 Pineville Dispatch

12784 Alexandria Dispatch

12816 Alexandria mobiles


Alexandria City Services

8016 Alexandria Transit Authority (ATRANS)

8048 ADA Van Service

8240 Building Services

13840 Electric

13872 Gas

13904 Water

13936 Wastewater

13968 Parks

14000 Utility (Meter Servicing)


14064 Motor Pool


14128 Traffic Signals

14160 Streets

14192 Animal Shelter


14256 Sanitation

There is a private TRS in the area using frequencies 853.3375; 856.1125; 856.5375; 857.1125; 857.5375; 858.5375; and 859.5375. Thanks to guidance from Larry Van Horn, and the FCC web site, I have discovered that this system is licensed to Tower Communications of Alexandria, Louisiana. They, in turn, contract out the system to area businesses. The following is nearly all of the active talkgroups, with some confirmations:

16 - Kay Radio and Electronics
1360 - Hixson Autoplex
2448 - Newschannel 5
41216 - Cabrini Outpatient Services (most active channel)

I will continue to monitor this sytem to obtain a more complete list of users.

One tip for the scanner enthusiast: A city map and a telephone book are great tools to make your Talkgroup ID confirmations.

I hope that this information will be of use to you.

Bill in Pineville, Louisiana

Cleveland, Ohio

I was curious as to whether the Pro-96 will be able to receive the city of Cleveland digital radio system, which is not APCO-25 compliant. Any information would be appreciated. Thank You.

Larry in Ohio

Like Memphis, Tennessee, the city of Cleveland uses Motorola digital radios -- but they do not follow the APCO Project 25 standard. The digital voice is done through an older vocoder (voice encoder/decoder) called VSELP (Vector Sum Excited Linear Prediction) instead of the IMBE (Improved Multi-Band Excitation) vocoder specified in the APCO-25 standard. Since there is currently no consumer scanner that can process VSELP, you won't be able to hear digital transmissions on the PRO-96.

Cleveland's system uses the following frequencies: 851.0125, 851.1375, 851.1875, 851.2375, 851.2875, 851.3375, 852.0125, 852.1375, 852.1875, 852.2375, 852.2875, 852.3375, 853.0125, 853.1375, 853.1875, 853.2375, 853.2875, 853.3375, 854.1375, 854.1875, 854.2375, 854.2875, 854.3375, 855.1375, 855.1875, 855.2375, 855.2875 and 855.3375 MHz.

Some Cleveland talkgroups:

48 003 Citywide 1

80 005 Citywide 2

144 009 Public Safety Common

208 00D Fireground Ops 1

240 00F Fireground Ops 2

272 011 Fireground Ops 3

304 013 Fireground Ops 4

336 015 Fireground Ops 5

368 017 Fireground Ops 6

400 019 Fire Prevention Bureau

592 025 Fire Alerts

688 026 Fire Dispatch

3472 0D9 Airport Fire/Rescue 1

3504 0DB Airport Fire/Rescue 2

3536 0DD Airport Fire/Rescue 3

4976 137 Police

5104 13F Police 1st District

5136 141 Police 2nd District

5168 143 Police 3rd District

5200 145 Police 4th District

5232 147 Police 5th District

5264 149 Police 6th District

Even though your scanner won't work with the VSELP transmissions, if you have a sufficiently fast connection to the Internet you can listen to a live "web feed" by following the links at

Pelham, New Hampshire


My town, Pelham, New Hampshire, just went to APCO-25 digital. I just bought a Radio Shack digital trunking scanner, the PRO-96. Now I need the codes they are using. Can you be of any help?

Mike in NH

Pelham is a town of about 11,000 people in Hillsborough County, on the Southern edge of New Hampshire just across the border from Massachusetts. For many years Pelham has used VHF frequencies for public safety; police transmission on 154.770 MHz from a tower on Marsh Road and fire dispatches on 158.745 MHz from Jeremy Hill Road.

As far as my records go, Pelham continues to use these frequencies. However, the nearby city of Nashua, New Hampshire is using a Motorola ASTRO system with analog and digital traffic on the following frequencies: 866.0500, 866.6000, 866.7750, 866.9750, 867.3625, 867.5500, 867.7500, 868.2625, 868.4500 and 868.5125 MHz.

8336 209 Highway Traffic
16784 419 Greater Nashua Transit Buses
32784 801 Fire Dispatch
32816 803 Fire Operations
32976 80D Emergency Medical Services
49168 C01 Police

If any readers have more information about the Pelham radio system, please drop me a line!

That's all I have room for this month. Please e-mail questions, comments, and frequency lists to, and you can find more information on my web site at Until next month, happy monitoring!

Comments to Dan Veeneman

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