RFS: P25 Transmissions on TG10055 off Chullora & Horsley Pk

[Longreach]

Mike, i have sucessfully got both my Pro96's working on the new GRN. i just got home from sydney. works very well and tracks quite well. im picking up horsley park from all the way out at douglas park and right up thru campelltown and ingleburn worked quite will. even in my grandmothers loungeroom in Belfield i got horsley park no problrm.
its crap audio but its no worse than the old G60 ops com 3 (TG54864).

ive been working with russell on this one and managed tro have a win
pm me if you would like the details.

cheers
Matt

[citabria]

It just works on a GRE500.
I'm willing to bet that the bandplans aren't even used on P25 GRN - they could be set to anything and have it still work.

They are not. As I understand pure P25 has a sub audible transmission at every press of the PTT which establishes all the system parameters. That is why I cannot understand why the GRE500 and now the PRO96 need the band plans.

Russell

OK cool, so that confirms my suspicion that they aren't used.

BTW - nothing at all in P25 is done subaudibly - its all done digitally using C4FM or CQPSK. The channel grants and system paramaters are all sent as TSBK packets on the control channel. The exisitng 3600 Smartzone Omnilink systems do, but not P25.

[rustynswrail]

It just works on a GRE500.
I'm willing to bet that the bandplans aren't even used on P25 GRN - they could be set to anything and have it still work.

They are not. As I understand pure P25 has a sub audible transmission at every press of the PTT which establishes all the system parameters. That is why I cannot understand why the GRE500 and now the PRO96 need the band plans.

Russell

OK cool, so that confirms my suspicion that they aren't used.

BTW - nothing at all in P25 is done subaudibly - its all done digitally using C4FM or CQPSK. The channel grants and system paramaters are all sent as TSBK packets on the control channel. The exisitng 3600 Smartzone Omnilink systems do, but not P25.

Agreed. I used the term 'subaudible' in the broad sense of the term.

R

[citabria]

Hehehe, that works for me - I guess anything you can't really hear is "sub-audible"

[Mike Alpha]

Mike, i have sucessfully got both my Pro96's working on the new GRN. i just got home from sydney. works very well and tracks quite well. im picking up horsley park from all the way out at douglas park and right up thru campelltown and ingleburn worked quite will. even in my grandmothers loungeroom in Belfield i got horsley park no problrm.
its crap audio but its no worse than the old G60 ops com 3 (TG54864).

ive been working with russell on this one and managed tro have a win
pm me if you would like the details.

cheers
Matt

Thanks Matt and Russell, I've been working on it too using the table and formula in the PRO96Com helpfile http://www.pa2600.com/pro96com.pdf but wasn't having much success. I was using 12.5KHz as the step, but when I changed it to 6.25 it started working. Here is a screencap showing the setting I'm using in ARC96, which will also work in Win96 for PRO96 users.
http://members.optusnet.com.au/~sydtrun ... ttings.jpg

All working now!

Mike

[Bigfella237]

I guess anything you can't really hear is "sub-audible"

Then again, everything P25 is transmitted as data, which is audible, so nothing on P25 is "sub-audible"!

Thanks Matt and Russell, I've been working on it too using the table and formula in the PRO96Com helpfile http://www.pa2600.com/pro96com.pdf but wasn't having much success. I was using 12.5KHz as the step, but when I changed it to 6.25 it started working.

Yep, you would absolutely need to set the step to 6.25KHz or your scanner will never be able to figure out the frequency from the LCN?

Frequency = Base + (LCN x Step)

BTW, even if you don't have to enter a bandplan, your scanner (or any TRN radio for that matter) still needs one, it's just that it can get it from the Ctrl Ch on a P25 system instead.

Andrew

[rustynswrail]

[quote="Bigfella237"]Then again, everything P25 is transmitted as data, which is audible, so nothing on P25 is "sub-audible"!

Alright, for crying out loud, there is an audible data transmission that is below the threshold of conscious perception, that preceeds the voice when the PTT is used.

Russell

[Longreach]

no worries mike all good.
ive entered all bases and offsets maybe i dont need all but its working and im not too worried about it. i mainly did it for all the LCN's all good it works so im leaving it alone.
cheers
Matt

[citabria]

Yep, you would absolutely need to set the step to 6.25KHz or your scanner will never be able to figure out the frequency from the LCN?

Theres two modes of P25 trunking. One mode uses bandplans, the other doesnt' - the frequency its transmitted across the control channel instead of transmitting a LCN and them multiplying by a step + base.

From my observations this afternoon, P25 GRN is using Implicit mode - in that the trunking packets transmit an LCN, which your radio then works out the frequency by the old "Frequency = Base + (LCN x Step)" method. An example of a Voice channel grant packet follows, and ill break it down to explain whats what.

Code: Select all

00 00 04 44 64 27 47 1E AB CC 64 F6  03/14 17:44:40 Group Voice Grant - Group: 10055 Channel: 4-1124(419.50000) Radio ID: 2010060

[/b]

00 = Opcode - Zero means this packet is a voice channel grant
00 = Manufacturer ID - Zero is a generic non-specific code that means any manufacturer ID will support and understand this packet. some packets are manufacturer specific
04 = Service Options - This tells the receiving radios if certain features are being used for this call like "Emergency" or encrypted control channel or full duplex or the call priority.

The next two bytes determine which bandplan is used and what LCN the voice channel is going to be for the conversation

44 = This byte is split into two - the first digit 4 tells the radio which bandplan we're using. In this case it's bandplan 4 as everyone else has figure out already. The second 4 is the start of the LCN
64 = so the LCN number is $0464 in Hexadecimal - Theres a bit of maths done to this number to work out what the final frequency is, but the important part is that we know we have to use bandplan number 4 in our radios (As confirmed by Mike/Matt/Rusty earlier on) We convert $464 to decimal and we get 1124. So thats our LCN. We multiply 1124 * 0.00625 = 7.025Mhz, and 412.475 + 7.025 = 419.5000Mhz which is the P25 voice channel on Chullora.

The next two bytes are the talkgroup number

27 = Convert this to decimal and we get talkgroup number 10055
47 = which is RFS according to what people have logged so far

The next three bytes are the originating caller ID (Radio ID)

1E
AB = which when we convert 0x1EABCC to decimal we get RID = 2010060
CC

Finally we have the Checksum bytes

64
F6

So to sum up, when we see a channel number in PRO96COM such as - Channel: 4-1124(419.50000) - We know that we are using bandplan number 4, and the LCN is 1124.

Or if you want to think about it in PRO96/DTS96 terms, its channel $4464 which = 17508

Cheers,
Matt

[citabria]

I guess anything you can't really hear is "sub-audible"

Then again, everything P25 is transmitted as data, which is audible, so nothing on P25 is "sub-audible"!

Yeah, that too! You're a cluey bloke!