Setting up trunking with no info!

[majoco]

Hi all. There is very little info available for Manawatu in New Zealand about trunking radio. I have two Uniden BCT8's that work very well on all the usual frequencies for the emergency services, aircraft etc. The NZ band plan says 406.1 to 420MHz is for Fleet Link and Team Talk Trunking and by searching through this band I come up with frequencies that are quite busy with NFM analogue signals, but the conversation that I hear are only one side so I guess I'm only hearing the input to the repeater - the signals are quite varied in strength which bears this out. The one-sided conversations end up with a burst of data and then on my receivers scanning resumes. I would have expected that some other frequencies have the output of the repeater but where? Mixed in with the received signals are some that sound like simplex which is even more strange! All my signals are in a band from 414.1875 to 417.3875 and seem to have a 6.25kHz channel spacing.
Any insight you can give will be appreciated.

 

[chief21]

Based on your description, it sounds likely that some type of trunking is in use. But there are many types of trunked radio systems and they all operate in different ways. Even systems from the same manufacturer can be different, depending on how they are set up and programmed. As a general rule (in the US), most commercial/government outbound UHF repeater frequencies are usually 5 MHz below the inbound frequencies. Of course, this might not hold true in NZ. It might be best if you could find a local resource that could provide the particulars for the system you're hearing.

 

[morfis]

A good start would be to try and identify the data at the end of the transmissions as that is almost certainly carrying control information.

Following will help

Trunked Radio - Signal Identification Wiki

Click the name of a signal to see more detailed information, possible decoding, and additional sound and waterfall samples

www.sigidwiki.com

 

[majoco]

Well, having gathered a selection of receivers including an old DVB SDR (which was miles off frequency!) I spotted quite a few control carriers and analogue voice channels too, but which voice belonged to which control remains a mystery. The control channels seemed to be mixed in the with the voice but there's nothing that seems to be 5MHz apart. If I listen to one of the strongest control channels on 414.6937MHz I would expect to find a voice channel on a round number away, say 419.6937 or 409.6937 but perhaps it's a different offset in NZ? My ancient Icom R7000 doesn't do 6.25kHz channeling and the SDR, although reasonably close frequency-wise now still wanders around more than needed. The data burst at the end of a QSO is too short to make any sense, just a second or so. Oh, well, more experimenting. The sounds of the control channel (thanks Morfis) are very close to DMR, dPMR or Motorola Tyrpe ll. I have some contacts in Tait and might chew their ears and see if they have any clues - might cost me a few beverages which could be worth it!

Thanks to all for the info.

 

[ka3jjz]

And you might try here just to get some preliminary info....

RadioWiki

www.radiowiki.org.nz

Mike

 

[majoco]

Thanks for that, Mike, but it's all just the analogue channels that I've already been through. The Police seemed to have abandoned their UHF frequency, haven't heard a peep on those frequencies for a long time but I get good coverage on the 76MHz frequencies.

 

[slicerwizard]

If I listen to one of the strongest control channels on 414.6937MHz I would expect to find a voice channel on a round number away, say 419.6937 or 409.6937 but perhaps it's a different offset in NZ?

No, one shouldn't expect to hear voice on a control channel input frequency.

As for band plans and in/out splits, that sounds like a question one would ask in the NZ forum, no?

 

[majoco]

No, one shouldn't expect to hear voice on a control channel input frequency.

Most of the voice channels I hear have only one half of the conversation which I would have thought were inputs. Are you saying that the system has two input and two output frequencies as well as the control channel? So far I have only found two frequencies where I can hear both parties of the conversation.

 

[chief21]

Most of the voice channels I hear have only one half of the conversation which I would have thought were inputs. Are you saying that the system has two input and two output frequencies as well as the control channel? So far I have only found two frequencies where I can hear both parties of the conversation.

Martin, I would agree that the "one-sided" frequencies are likely inputs to the repeater. It is also likely that the "two-sided" frequencies are repeater outputs. To help with your sleuthing, all of the repeater output (voice) frequencies, as well as the control channel, will be in the same general range and, typically, all of the input frequencies will be either substantially higher or lower than the outputs. If you are able to confirm that the related frequencies do, in fact, employ 6.25 kHz spacing, that could be a hint as to the type of trunked system since only those systems employing digital modulation would be using such a narrow bandwidth.

 

[majoco]

All of the frequencies I have discovered are multiples of 6.25kHz although some do fall on the 12.5 and 25kHz frequencies - perhaps I should go through my lists again and see if I can make groups of the frequency spacing. I don't think they're digital as I can copy them all on FMN on three separate receivers - even my R7000 which is certainly analogue only! I might have to get a much later RTL SDR which hopefully will have better stability and hence read the frequency more accurately. Mornings are most busy, lunchtime very quiet, evening non existent, so I have to put off my usual morning tasks to get the best answers!

 

[chief21]

All of the frequencies I have discovered are multiples of 6.25kHz although some do fall on the 12.5 and 25kHz frequencies

I should note that even 12.5 or 25 kHz spacings are ALL multiples of 6.25 kHz. It doesn't necessarily follow that the channels actually use 6.25 kHz modulation.

If you are familiar with RTL-SDR receivers, have you ever heard of a PC application called Unitrunker? If it is available for download in NZ, it could possibly give you all the details on your mystery system. Unitrunker works in concert with an RTL-SDR dongle.

 

[Ubbe]

It could be a MPT-1327 system that are popular in NZ and AUS. It sound very much like one.
Download this program that even works using loudspeaker audio from some scanners.
It can control a scanner using a serial connection to follow calls and it allows talk groups
to be avoided.

Snabel

/Ubbe

 

[majoco]

I've got a newer RTL-SDR on order so I'll have a play with that - from what I understand two are required to scan Talk groups, but we'll see.
Thanks for all the info.

 

[zl1dfa]

Well, having gathered a selection of receivers including an old DVB SDR (which was miles off frequency!) I spotted quite a few control carriers and analogue voice channels too, but which voice belonged to which control remains a mystery. The control channels seemed to be mixed in the with the voice but there's nothing that seems to be 5MHz apart. If I listen to one of the strongest control channels on 414.6937MHz I would expect to find a voice channel on a round number away, say 419.6937 or 409.6937 but perhaps it's a different offset in NZ? My ancient Icom R7000 doesn't do 6.25kHz channeling and the SDR, although reasonably close frequency-wise now still wanders around more than needed. The data burst at the end of a QSO is too short to make any sense, just a second or so. Oh, well, more experimenting. The sounds of the control channel (thanks Morfis) are very close to DMR, dPMR or Motorola Tyrpe ll. I have some contacts in Tait and might chew their ears and see if they have any clues - might cost me a few beverages which could be worth it!

Thanks to all for the info.

This really is a discussion for the NZ forum, but ...

There are two sources of information that will clarify all this for you. First is the PIB23 publication from Radio Spectrum Management. It is available here: Mobile service bands in New Zealand (PIB 23)

PIB23 lists all the land mobile channels, so you can associate the frequency you find with an actual channel.

The other source of information is the register of radio frequencies, which you can search here: Home

That allows you to search for a license, which will allow you to conclusively figure out who is transmitting what and where. (Note, Police/Fire licenses are not listed).

The channeling is not 6.25KHz.

Looks like the frequency you call "419.6937" is actually 419.700 MHz, a Vital (Teamtalk) frequency broadcasting from Bastia Hill (Topo50 ref BL32 768783). Try searching for frequencies between 400 & 420 MHz in Manawatu, and all will be revealed.

D.