SDRTrunk MPT1327 Issue

[rocky28965]

I am using the latest SDRtrunk v0.6 version.
I have to manually program the channels as Radio reference doesn't cover my area.
I have setup some DMR channels and they work ok but I am having problems with a MPT1327 channel.
It has 1 control channel & 2 talk channels.
I know this because I have tracked it on Unitrunker.
I have added the 3 frequencies and it shows up as MPT1327 protocol in the playlist.
In now playing, the control channel shows yellow and all looks good but when a calls come through there is no audio.
In events, the correct channel numbers show up as "Invalid Channel Map - No frequency for channel"

I am assuming I have to do something with the channel map editor.
However I have tried adding a similar MPT1327 site from Radio Reference for another part of the country and it does nothing in the editor.
But of cause it's not going to receive anything as it's out of range.

 

[DSheirer]

You'll need to setup the channel map so that sdrtrunk knows how to tune to the traffic channels and decode the audio. You'll only want to load just the control channel frequency into the channel configuration and don't include the other 2 frequencies.

 

[morfis]

MPT1327 traffic channels are allocated by a number not a frequency.
The software needs to know which frequency relates to the channel number.

For most systems this will be fairly straight-forward as the channel plan will follow a logical format so all you need to add is the base frequency of the plan and the step size
For software such as sdrtrunk you'd need to enter the control frequency as a channel and then in the channel plan editor you'd put the base frequency and the step size -no need to enter any traffic channel frequencies as the software knows what to tune.

Some systems use a non-logical plan and for these you would have to manually add each channel number / frequency pair in the map (assuming sdrtrunk works with that type of system)

 

[enosjones]

I know with trunkview it gives the LCN for mpt1327 system, only recently radioreference added a feature where the mpt1327 systems will now allow 3 digit lcn numbers. Then u can apply it to sdr trunk..

 

[rocky28965]

MPT1327 traffic channels are allocated by a number not a frequency.
The software needs to know which frequency relates to the channel number.

For most systems this will be fairly straight-forward as the channel plan will follow a logical format so all you need to add is the base frequency of the plan and the step size
For software such as sdrtrunk you'd need to enter the control frequency as a channel and then in the channel plan editor you'd put the base frequency and the step size -no need to enter any traffic channel frequencies as the software knows what to tune.

Some systems use a non-logical plan and for these you would have to manually add each channel number / frequency pair in the map (assuming sdrtrunk works with that type of system)

When you say base frequency, are you referring to control channel?
The step size in this system is quite large.

The frequencies and channels are:
105 415.3125
144 415.8000
Ctrl Chan 415.5500

 

[morfis]

When you say base frequency, are you referring to control channel?
The step size in this system is quite large.

The frequencies and channels are:
105 415.3125
144 415.8000
Ctrl Chan 415.5500

No. Base frequency would be channel 0 and that from which others are derived in a logical plan. Not all frequencies need be used and the base freq need not be in the actual portion of a band 'allocated' for a particular service (they aren't usually so strange though!).
The step size in your system is not 'quite large'. I don't recall any system using a step size that was anything but a standard channel allocation.

System Channel tt = base freq + (tt x step)

Using your examples and assuming the plan is logical

Base freq = 415.3125 - (105 x step size)

Again an assumption - the step size will be a common value and here I'll guess it's 12.5 kHz.

So we have Base freq = 415.3125 - (105 x 0.125)
base freq = 414.0000

Check with the other pair and if correct the numbers should match

If you monitored the maintenance data on the voice channels you'd probably see cleardowns to the channel number which equates to the control channel and that would give you another check that your plan is 'logical' (I don't know if sdrtrunk shows the data as I don't use the software...there are certainly other bits of software that will show it)

So if the above is correct (check using your other pair) you'd set up a system with your control channel and a plan with 414.0000 MHz as the base frequency and 12.5 kHz as the channel step. The software should take care of the traffic channels (which is handy as systems sometimes have other channels available that are only used if traffic is very high).

 

[rocky28965]

No. Base frequency would be channel 0 and that from which others are derived in a logical plan. Not all frequencies need be used and the base freq need not be in the actual portion of a band 'allocated' for a particular service (they aren't usually so strange though!).
The step size in your system is not 'quite large'. I don't recall any system using a step size that was anything but a standard channel allocation.

System Channel tt = base freq + (tt x step)

Using your examples and assuming the plan is logical

Base freq = 415.3125 - (105 x step size)

Again an assumption - the step size will be a common value and here I'll guess it's 12.5 kHz.

So we have Base freq = 415.3125 - (105 x 0.125)
base freq = 414.0000

Check with the other pair and if correct the numbers should match

If you monitored the maintenance data on the voice channels you'd probably see cleardowns to the channel number which equates to the control channel and that would give you another check that your plan is 'logical' (I don't know if sdrtrunk shows the data as I don't use the software...there are certainly other bits of software that will show it)

So if the above is correct (check using your other pair) you'd set up a system with your control channel and a plan with 414.0000 MHz as the base frequency and 12.5 kHz as the channel step. The software should take care of the traffic channels (which is handy as systems sometimes have other channels available that are only used if traffic is very high).

Sucess and I thank you for your assistance.
However I did finish up using slightly different settings in the channel map editor.

The 12.5 kHz step seems to be correct.
Base frequency of 414.000 didnt work.
Tried 415.3125 as base and it works great

 

[morfis]

Base frequency of 414.000 didnt work.
Tried 415.3125 as base and it works great

Glad you've got it working but the numbers make no sense.

For a logical plan an MPT1327 channel is at: Base frequency + (Channel number x Channel step)

If you have set the base frequency in the plan to 415.3125 MHz and step to 12.5kHz the software would be tuning to 416.6250 and 417.1125 on the traffic grants

In your example:
TSC is on channel 415.3125 (channel 124) with known traffic channels using 105 (415.5500) and 144 (415.8000)
This only works if the base frequency is 414.0000

Custom bandplans were (are?) less common and if sdrtrunk supports them it will have plan settings that require all channel/frequency pairs be entered manually.

Is the network used by multiple companies? Eg. several taxi companies, transport companies etc? The radio ID is in the form PrefixNumber (pppnnnn). Generally the prefix will radios from a single company
so in your screenshot radios 006-2355, 006-2218 and 006-2210 would likely be from a single company and 003 prefix a different one.

 

[rocky28965]

Perhaps it's an illogical system.
I don't know how they work.
I had no way of knowing the step size or what the base frequency was.
I found the 415.5500 control channel in a scan.
Put that into unitrunker and with a couple of SDR dongles, found the only 2 channels being used.
It showed as a MPT-1327 system and listed the channels as 105 & 144.
Being 415.3125 & 415.8000 respectively.
This is a semi rural area and there is very little traffic on the system.
From what I have heard it would appear to be several different companies.

 

[morfis]

That's me totally confused then! If you set the plan with a base of 415.3125 and step of 12.5kHz the software wouldn't tune your voice channels.


Most hobby software doesn't support custom plans
Custom plans require explicit channel number/frequency pairs to be programmed to work.
This isn't what you say you have done?

The frequencies and channel numbers you found follow a logical plan where you would set up a system with your control channel then a plan using the calculated base and step size.