Help w/ MPT-1327

ac7xc · #1 (**permalink**) 10-11-2006, 10:09 PM

I am trying to decode a MPT-1327 system in Yamhill County, Oregon USA however I am having problems figuring out the channels. In the Trunkview Adjacent Channel data I get:

Code:

- ID 0019:
ID: 0009   Ch: 044
ID: 0051   Ch: 564

in the Voice Channels view I get

Code:

- ID 0019:

How do I convert these to frequencies?
Anyone know the base, step and offset for the systems in the USA?
The control channel frequency is 460.1000
For this example I put

Code:

 420 MHz Base
12.5 kHz step
offset 2

basically because that is what is set for European systems so I tried it.

TIA

Unitrunker · #2 (**permalink**) 10-11-2006, 11:00 PM

At the end of a call, the voice channel will have a "GTC" or Go To Channel message with the channel number of the active control channel. I *think* Trunkview will capture this number.

Once you know the channel # of the control channel and the frequency of the control channel you can make a guess as to the band plan for the system.

Jay911 · #3 (**permalink**) 10-11-2006, 11:02 PM

What are the other frequencies licensed to this user in the FCC database? The "ID:" stuff are talkgroup and radio IDs, like with other trunk systems. The "Ch:" or Channel details are what are useful to you. See, MPT1327 systems don't say "go to 462.1625", they say "go to channel 044". This follows a channel plan developed with the base/step/offset values in the last part of your message. Unfortunately, Euro systems don't really match up with North American systems all that well, so your base/step/offset values might be all off.

DaveH · #4 (**permalink**) 10-11-2006, 11:39 PM

I don't live near this system and can't get Trunkview to run on my
system so can't help you there. I'd find the system frequencies if
possible from the FCC database or other means first.

MPT systems can have multiple base/offset/step. Ignore the European
numbers as they would not apply. The base could be anything above
the lowest frequency in use but not likely below 451MHz. By step I
presume you meant 12.5kHz, not MHz. Step could be 6.25kHz to allow
for narrowband channels, as it is for a large system near me. Hopefully
Trunkview can handle these properly because Tronquito (Trunkito)
didn't, causing roundoff errors.

Dave

Jay911 · #5 (**permalink**) 10-12-2006, 12:25 AM

I'm not too versed on the FCC lookup... you get a ton more information than on the Canadian equivalent, but it's set up in ways I can't begin to comprehend.

I'm *guessing* that the frequencies of this system are 460.05, 460.1, 460.1875, 460.275, and 460.4125. Those are the ones that appear to be similar in this FCC lookup.

The best way to do things right now is monitor it with trunkview but do NOT let trunkview adjust your radio settings - whether you turn off the ability or leave the cable unplugged or whatever. Tune to the control channel. When the system gives a GTC (Go To Channel - Voice) command and gives a channel number, write down the channel number, then check each of those frequencies above to figure out which one that is. Write that down along with the channel number. Now, if you let the radio listen on that voice channel until the call closes, there's a short data burst at the end of the call. Trunkview will report that, as rfmobile said, as "Call clear-down / Return to Control Channel" and a channel number. That channel number will be the channel number for your active control channel. Once you get that settled, you can make a chart with a spreadsheet, and extrapolate the channel values for the other channels, as well as the base and spacing. In my experience with the MPT systems in my area (all in the 420-425 mhz range), 12.5 khz spacing is proper.

If you still have trouble after getting some data, fire it my way and I'll try to figure something out. Like I said, I have a bunch of MPT systems in my region, so working this junk out is getting to be old hat.

Comint · #6 (**permalink**) 10-12-2006, 02:00 AM

Quote:

Originally Posted by ac7xc

. . . In the Trunkview Adjacent Channel data I get:

Code:

- ID 0019:
ID: 0009   Ch: 044
ID: 0051   Ch: 564

in the Voice Channels view I get

Code:

- ID 0019:

How do I convert these to frequencies?

You can't - ID: 0019 is the Number of the Site you are monitoring. ID: 0009 and ID: 0051 are two other Sites in your area, although you may not be able to hear them unless you have an outdoor antenna.

The Trunkview website has an explanation on how to determine the required frequency / base details.

Comint

morfis · #7 (**permalink**) 10-12-2006, 02:01 AM

Check the trunkview website for a guide to working out the plan in use.

http://www.linato.net/trunkview/?How...base_frequency

There is NO standard plan as such anywhere in the world (there are lots of standard plans!).

As long as the system uses a logical channel plan (there are many that don't and Trunkview cannot track these) it is fairly easy to work out the settings as long as you know/see one of the following:
2 frequency/channel pairs
you get correct 'cleardown' messages at the end of voice transmissions
'call maintainance' messages are sent between overs

As a start use an offset of 2 (this really shouldn't even be in the config as it confuses people). Channel spacing will usually conform to the normal spacing in the band. Trunkview copes fine with 6.25KHz if that is what is being used (Tronkito doesn't correctly implement that as the author didn't have any systems with 6.25KHz channel steps and didn't know that other people did).

ac7xc · #8 (**permalink**) 10-12-2006, 04:11 PM

Ok i have tuned to the voice channels in this system and there is no databurst on the repeater at the end of the tansmission or when the repeater drops. I have heard that this system may be in conventional mode.??
Is it posssible the end of transmisssion data burst is not allowed through the repeater by a filter of some type?
This is the system I am trying to monitor:
http://www.radioreference.com/module...me=RR&sid=2943
the control channel is 460.100 for site 3 the system I can receive.
the control channel for site 2 is 453.2375 which I can barely receive, but not decode.
for site 1 I can not receive it at my qth.

800crazy1 · #9 (**permalink**) 10-12-2006, 07:25 PM

new to the mpt-1327 systems , i own a 396t and was wondering if this radio will trunk track a mpt-1327 system. the system i would like to track is a 900mhz system at the MOHEGAN SUN CASINO in UNKUSVILLE CT. if so , ill ask for help from the replys on this subject to maybe help me program it. if it cant , oh well , its a dead duck ! thanks in advance for your help.

Unitrunker · #10 (**permalink**) 10-12-2006, 09:02 PM

Quote:

Originally Posted by 800crazy1

the system i would like to track is a 900mhz system at the MOHEGAN SUN CASINO in UNKUSVILLE CT. if so , ill ask for help from the replys on this subject to maybe help me program it. if it cant , oh well , its a dead duck ! thanks in advance for your help.

No, the radio won't but you might be able to use a program like TrunkView together with your radio.

Comint · #11 (**permalink**) 10-13-2006, 05:01 AM

Quote:

Originally Posted by ac7xc

Is it posssible the end of transmisssion data burst is not allowed through the repeater by a filter of some type?

Considering the way some MPT-1327 systems have been set up, anything is possible.
However, the whole idea of the Clear Down message, is to tell the mobile to return to the Control Channel to await the next call, so filtering it out would appear to defeat the purpose. If a mobile misses a Clear Down message, it has to waste time scanning the band looking for a Control Channel again.

You could try these frequencies as possible Base frequencies:- 452.9875, 453.2125, 453.2875, or 453.5875, and then adjust for any error on a GTC Voice.

Comint

800crazy1 · #12 (**permalink**) 10-13-2006, 09:51 AM

rfmobile , thanks for the reply

morfis · #13 (**permalink**) 10-13-2006, 11:56 AM

Quote:

Originally Posted by Comint

Considering the way some MPT-1327 systems have been set up, anything is possible.
However, the whole idea of the Clear Down message, is to tell the mobile to return to the Control Channel to await the next call, so filtering it out would appear to defeat the purpose. If a mobile misses a Clear Down message, it has to waste time scanning the band looking for a Control Channel again.
Comint

Cleardown messages are not a requirement of an MPT1327 system. More often than not, on systems with 1 control channel, the control channel number is pre-programmed and the radios don't actually use the cleardown.