One for the old-timers: IMTS selcall format?

[Johnny Grep]

Hi there,

We have an ancient VHF mobile radio system with what seems to be IMTS base station equipment (we are in the 152-157 range). We use Vertex FTL-2011 99ch radios and I think the base station controllers are Glenayre systems. Normal calls are made by Selective Calling (we transmit our 7-digit radio ID in DTMF and then transmit the 7-digit destination radio ID, the base station sends a set of tones that resemble modat or select-5 to unsquelch the radio) and we can also make phone calls. We usually "register" the radio every morning to tell the system on what channel (region) we are listening to, and if we are calling a radio in a different region (channel) then both channels are patched until we close the call (dtmf radio ID + #).

Can anyone tell me if this is a modified IMTS radiotelephone system or is this proprietary? I've seen Zetron & Glenayre equipment at the base station sites, and some of the frequencies are close and/or identical to the Yx and Jx channels.

Also, I've seen the tone chart - it does not seem to resemble MODAT, GE or anything I know of - it is custom-programmed in each Vertex radio. I was wondering if I could program these custom selcall tones in a Motorola mobile radio? (e.g. 1981hz for 0, 1124hz for 1, etc)

[Bill_G]

Does the system transmit a marked idle tone when there is no activity? If not, then it is a custom system of some sort. If it does, then you can Google IMTS for plenty of info about this now defunct standard. Judging by your description, it is a custom system, probably innovative for it's time, and obviously still supported if you can purchase mobiles that can be programmed to function within it. I would talk to your radio service personnel to find out more details.

[k2hz]

What you describe is definitely not IMTS.

IMTS used 2150/1633 pulses for mobile ANI and dialing and 2000/1800 for base to mobile selective call. A constant 2000Hz base idle tone was a key part of the system along with other tones for a connect handshake between mobile and base prior to ANI or dialing.

What you have sounds somewhat like "AMTS" and was used by some Radio Common Carrier systems.

AMTS used DTMF for mobile ANI and dialing and 1500/1700 for base to mobile selective call.

I think there were other variations called "PMTS" and "IPTS" that were DTMF based but I never encountered them. I was factory trained on Glenayre terminals and maintained a telco Glenayre IMTS system. I believe that AMTS was also supported by the terminals plus some other protocols with 2805 signaling.

[Johnny Grep]

Well, my system doesn't sound like it's an IMTS system, judging from your descriptions. We use Zetron 7D remotes as well as dispatch consoles.

I'll post an audio sample of the signaling between the radios, base stations & dispatch consoles... this is quite interesting.

The FTL-2011's seem to have custom programmed selcall tones... weird. These radios seem to support select-5, CCIR & modat?!

P.S. it IS a telco system.

[Johnny Grep]

Well, Google helped me out - we're using a RACS system (Zetron 7032). FFSK signaling for the 7D consoles, DTMF & Selective Tone for the Vertex mobiles.