Mobile Data Terminal format change in Northern Illinois

train_radio_guy · Post by **train_radio_guy** » Mon Sep 11, 2006 8:18 am

Hey Guys,

I was wondering if anyone had noticed that the MDT system still in place in Northern Illinois (on 857.7375 MHz), which operates on the ALERTS Network, has changed speed &/or formats. For the longest time they were still utilizing the MDC-4800 protocol, much like the Ardis system, but now it seems like the format has changed. Audibly, it sounds like a quicker buzzing sound or saw-tooth pattern, inter-space with bursts of data.

Does anyone happen to know what format they're running these days? Up until very recently, several of the smaller departments around us were still using the older Motorola MDT-9100 terminal.

I know some agencies have been utilizing the CDPD modems, through the local cellular providers, but this transmitter is still active on the MDT frequency, so it's reasonable to assume that someone is still using the system, albeit a different format.

Any info on this subject would be welcome.

Thanks,

trg,

Batwings21 · Post by **Batwings21** » Tue Sep 12, 2006 9:34 am

If the site you are talking about is indeed part of ALERTS. then most of them are and have been rdlap 9.6 which is 9600 baud for some time, at least 6 years. there are some sites in northern illinois that operate on rdlap 19.2 which is 19200 baud.

train_radio_guy · Post by **train_radio_guy** » Tue Sep 12, 2006 1:50 pm

Well the sites in Rockford & DeKalb were still running MDC-4800, up until about two years ago. A friend at the county had mentioned there was a change, in either the format and / or the speed, since some of his older equipment was no longer functioning.

As a favor, I told him that I'd look into it, and make a few inquires. If the current system is running RD-LAP at either 9.6 or 19.2 baud, then his older gear is definitely not compatible.

I've been out of the radio business since 1998, so I suspected the technology would have changed considerably concerning wireless data transmission. For better coverage, I'm actually surprised most departments haven't switched over to a cellular based technology, like CDPD or CDMA.

Who actually maintains the wireless portion of the ALERTS Network? Perhaps the State of Illinois Comm. Guys, or has it been outsourced, much like everything else in the communications industry?

Batwings21 · Post by **Batwings21** » Tue Sep 12, 2006 3:59 pm

The codeplugs I have been putting into vrm's for 6 years have only had rdlap 9.6 channels into them, until about a year and a half ago, they added some 19.2 channels, maybe the 4800 channels were not included because the spectra radio could not switch format on the fly, the mcs based units can, enabling them to switch between 9.6 and 19.2 its called rdlap dual. I checked the freqs and here are the current alerts freqs, yours is not listed, maybe it is not alerts, but another datatac system that is connected to leads.

Number RNC/NCP ID
1 821.36250
2 821.38750
3 821.48750
4 821.86250
5 821.91250
6 821.98750
7 822.36250
8 822.43750
9 822.48750
10 822.86250
11 822.96250
12 811.26250
13 813.43750
14 810.96250
15 813.71250
16 814.46250

train_radio_guy · Post by **train_radio_guy** » Tue Sep 12, 2006 5:24 pm

After completing a quick search of the frequency pair 857.7375 / 812.7375 on the FCC's web, I found 5 separate callsigns for this frequency in Illinois. The transmitters are scattered from Champaign to Rockford, and well into the suburbs & downtown Chicago.

And the licensee is (drum roll.......):
ILLINOIS CRIMINAL JUSTICE INFORMATION AUTHORITY.

Your frequencies also come back to the state, so I suppose they could have multiple systems; each for a separate department or district, although that would seem rather redundant & costly. Typical for Illinois though. It could also be due to frequency availability in each area too.

With all these different systems deployed, it would be very interesting to research their respective use & application, if for no other reason than simple curiosity. However, I would be concerned that someone might misconstrue my interest in this subject, and the result would be akin to 'kicking the ol' hornet's nest.' That's the last thing anyone needs.

Thanks for your info.

trg,

apco25 · Post by **apco25** » Tue Sep 12, 2006 11:07 pm

Many, many departments are switching from ALERTS 800 RD-LAP to EVDO Verizon broadband cards (via VPN) which are replacing the older CDPD cards as first used by IWIN.

Nice technology, but relies on a public carrier ( gee, isn't that what sprint/nextel wants!) and the functionality of being able to msg any other ALERTS user anywhere in the state is being lost (mobile side that is)

train_radio_guy · Post by **train_radio_guy** » Wed Sep 13, 2006 2:20 pm

What ever change took place locally, it's happened within the last year, or so I'm told. I'd heard something about Verizon Wireless rolling out some sort of new wireless card, for the migration of the older CDPD customers to the newer technology.

I haven't personally had much experience with the cellular or SMR based wireless cards, but the reports are mixed. Some folks can't say enough about the service, while others say it leaves a lot to be desired. Obviously coverage comes into to play, but the lack of ability to send messages to any other ALERTS mobile user, anywhere in the state is a big deficit.

What happened to interoperability?

Back when the dedicated networks were the norm, it was interesting to see how some of the old-school radio techs could identify the protocol or format by ear, just by listing to the transmitter on a their service monitor (Golay, POCSAG, CCIR, MDC-1200/4800). Those days are long gone with the advent of newer technologies.

One of the local shops that maintained their own local wireless data network, used to monitor traffic on their system with a laptop, some sort of homebrewed interface, and an Icom IC-R100! Those were some interesting times....

apco25 · Post by **apco25** » Wed Sep 13, 2006 5:47 pm

The verizon option is no different than their broadband EVO offering. THe departments are accessing their home CAD systems and LEADS data via VPN connection over the EVDO card like any other internet traffic.

Batwings21 · Post by **Batwings21** » Thu Sep 14, 2006 8:05 am

Just to make it clear, I was not doubting who operated that channel, but the system known as ALERTS is those freqs I listed as far as I know. I have probably worked on hundreds of vrm's on alerts, and your freq was not inlcuded in any. Maybe that was a older system that ran at 4800, I just dont't understand why it would not have been included in the rdlap system. Unless there was hardware that they had to support but would not work on rdlap, but I have seen 9100t terminals do rdlap as well as mdc-4800, maybe the kdt480?

apco25 · Post by **apco25** » Thu Sep 14, 2006 11:18 am

It would be a simple matter to allow porting back to ALERTS users to keep the msg functionality. Of course PSAP LEADS terminals can still msg each other, but the in car ability sure was nice.

train_radio_guy · Post by **train_radio_guy** » Mon Sep 18, 2006 5:57 pm

It sounds like things have changed significantly since I worked in the 2-way market. Our shop handled the basic servicing of the older terminals, for some of the smaller departments. Otherwise, the local MSS fielded most of the contract work.

If memory serves me correct, the boss a had laptop running special software (Which he received from our /\/\ Rep.), setup with some sort of gadget connecting it to an IFR service monitor, on the workbench. As it goes, I think he could hit a key on the keyboard of the MDT, & see the character appear on the screen of the laptop. Sort of a rudimentary test jig to verify the thing was working I suppose. It looked like a 'basement special' solution, but it worked & served its purpose at the time.

He handled most of that work, so I wasn't usually involved in the MDT stuff too much, unless he was tied up with something else. With the changes in technology, I doubt it's even possible for a 2-way shop to make a simple test jig like that one anymore. Progress?

- trg,