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DSD+: How Come I Can Listen To One P25 System But Not Another?

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#2
Sometimes not all talk groups are configured for Phase II. Thats why you can hear some and not the others.
 
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#3
Does DSD+ let you hear only Phase I but not Phase II? I have 2 dongles running, but on the Hillsborough system, the VC instance of FMP24 doesn't tune to anything even though there's voice calls showing.
 
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#5
So you mean a Phase II system can have talk groups that aren't TDMA? The Clearwater system is listed as Phase II, but I can track and listen to talk groups on DSD+.
 

dave3825

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#6
That's odd, are you sure you can hear Clearwater and not Hillsborough as you listed? All the tg on Clearwater system are listed as mode "T".

And the ones for Hillsborough are listed as modes D and T. I would not think you should have a problem hearing mode D audio, on Hillsborough. I listen to a Project 25 Phase II system and can hear audio fine on all the "D" tg's. I could be wrong or maybe my system is set up different.


D = Digital Talkgroup
T = TDMA Capable Talkgroup





.
 
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#7
That's basically it. I can hear Clearwater but not Hillsborough. They're both listed as Phase II. If DSD+ doesn't do Phase II, then I shouldn't be able to hear either one. So I guess a Phase II system can have talk groups that are only Phase I, but not the other way around? But DSD+ can decode just the control channel data on Phase II but not the audio?

Exactly what is the difference between a Phase I and Phase II control channel? DSD+ only displays "P25" without telling if it's I or II.
 

dave3825

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#8
The way I understood it with phase 2 was if the tg was labeled D then it was phase 1 audio and if it was labeled T it was phase 2 audio. At-least that's whats working for me. On any phase 2 system in my area, I am able to hear tg's labeled D...I can not hear the ones labeled T...
 

Forts

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#9
If a talkgroup is identified as 'D' it's Phase 1 only. A talkgroup identified as 'T' means it's Phase 2.... BUT! That talkgroup can also carry Phase 1 traffic as well. It basically works like this... a system may be a mix of Phase 1 and 2 traffic. If all the radios on talkgroup XYZ are shiny new APXs then the talkgroup runs in Phase 2 mode, but if an older radio (XTS5000 for example) joins the talkgroup, then everyone gets reverted back to Phase 1 for compatibility. Some systems may be purely Phase 2 and others might not allow Phase 1 radios to affiliate to a Phase 2 group.
 
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#11
That's basically it. I can hear Clearwater
If you're hearing it (whatever it is) with DSD+, it's unencrypted Phase I audio.


but not Hillsborough.
Then it's Phase II audio.

DSD+ will auto-mute encrypted Phase I audio, but you'll often hear bits of it before the muting kicks in.


They're both listed as Phase II. If DSD+ doesn't do Phase II, then I shouldn't be able to hear either one.
Just because something is listed as Phase II, it doesn't mean there is never any Phase I traffic.


So I guess a Phase II system can have talk groups that are only Phase I, but not the other way around? But DSD+ can decode just the control channel data on Phase II but not the audio?

Exactly what is the difference between a Phase I and Phase II control channel? DSD+ only displays "P25" without telling if it's I or II.
There is no such thing as a Phase II control channel. All P25 control channels are 9600 bps, same as Phase I voice channels.

What you want to know is not whether a control channel is Phase I or Phase II, but whether the talkgroup calls are. So just look at the calls in the event log - do they have slot numbers? If so, they're Phase II calls.


2016/08/12 19:57:30 Freq=770.531250 NAC=3C6 Enc Group call; TG=294 [42 Tac] RID=13213 Ch=773.58125 5s
2016/08/12 19:57:31 Freq=770.531250 NAC=3C6 Enc Group call; TG=291 [42 Div] RID=52009 [42 Dispatcher] Ch=773.31875 2s
2016/08/12 19:57:34 Freq=770.531250 NAC=3C6 Enc Group call; TG=83 [City Properties (TDMA)] RID=16817 Ch=772.64375-2 2s
2016/08/12 19:57:34 Freq=770.531250 NAC=3C6 Enc Group call; TG=292 [43 Div] RID=10054 Ch=772.33125 6s
2016/08/12 19:57:34 Freq=770.531250 NAC=3C6 Affiliation; RID=14254 TG=292 [43 Div] ACCEPT
2016/08/12 19:57:34 Freq=770.531250 NAC=3C6 Enc P-Group call; TG=279 [32 Div] RID=10404 Ch=771.30625 Pri0 3s
2016/08/12 19:57:35 Freq=770.531250 NAC=3C6 Enc Group call; TG=291 [42 Div] RID=11176 Ch=773.31875 8s
2016/08/12 19:57:38 Freq=770.531250 NAC=3C6 Enc Group call; TG=83 [City Properties (TDMA)] RID=16889 Ch=771.05625-2 3s
2016/08/12 19:57:38 Freq=770.531250 NAC=3C6 P-Group call; TG=304 [53 Div] RID=52015 [51/53 Dispatcher] Ch=773.58125 Pri0 16s
2016/08/12 19:57:38 Freq=770.531250 NAC=3C6 Registration; RID=14681 TG=296 [51 Div] ACCEPT
2016/08/12 19:57:38 Freq=770.531250 NAC=3C6 P-Group call; TG=327 [PKE East] RID=11045 Ch=773.36875 Pri0 6s
2016/08/12 19:57:38 Freq=770.531250 NAC=3C6 Registration; RID=13755 TG=327 [PKE East] ACCEPT
2016/08/12 19:57:40 Freq=770.531250 NAC=3C6 Registration; RID=24586 TG=1607 [SE Standby] ACCEPT
2016/08/12 19:57:41 Freq=770.531250 NAC=3C6 Enc Group call; TG=292 [43 Div] RID=52010 [43 Dispatcher] Ch=772.33125 2s
2016/08/12 19:57:42 Freq=770.531250 NAC=3C6 Enc P-Group call; TG=279 [32 Div] RID=52006 Ch=772.91875 Pri0 4s
2016/08/12 19:57:45 Freq=770.531250 NAC=3C6 Enc Group call; TG=291 [42 Div] RID=52009 [42 Dispatcher] Ch=773.31875 9s
2016/08/12 19:57:45 Freq=770.531250 NAC=3C6 Group call; TG=84 [TCHC (TDMA)] RID=16875 Ch=771.53125-1 3s
2016/08/12 19:57:46 Freq=770.531250 NAC=3C6 Enc P-Group call; TG=327 [PKE East] RID=52003 [PKE dispatcher] Ch=772.64375 Pri0 3s
 
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#12
Thanks for the replies. So if the control channel is only called "P25", then it can do both Phase I and II? I thought back when P25 was invented, there wasn't any TDMA yet. If they've added TDMA since then, wouldn't the control channel protocol have to have changed? If a Phase I radio requests a call grant via the input of the control channel, but another Phase II radio requests a call grant via the same control channel, wouldn't the control channel have to include the slot number on the output when it tell all the radios on the talk group where to go next? I thought the protocol would be different if there's a slot number versus no slot number.
 
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#13
To support Phase II, a new bandplan definition message was added to the control channel stream. No fundamental changes had to be made to the control channel format.


Phase I bandplan definition; defines frequencies for channels 1-0 to 1-4095:

IDEN_UP ID=1 Base=762.00625 Offset=+30 Spacing=6.25 BW=12.5


Phase II bandplan definition; defines frequencies and slots for channels 3-0 to 3-4095:

IDEN_UP_TDMA ID=3 Base=762.00625 Offset=+30 Spacing=12.5 BW=12.5 Slots=2


Phase I channel grant to channel 1-1524 (771.53125 MHz):

GRP_V_CH_GRANT PRI4 TG=1605 RID=52219 ch=771.53125


Phase II channel grant to channel 3-1524 (771.53125 MHz, slot 1):

GRP_V_CH_GRANT PRI4 TG=84 RID=16875 ch=771.53125-1

Phase II channel grant to channel 3-1525 (771.53125 MHz, slot 2):

GRP_V_CH_GRANT PRI4 TG=84 RID=16870 ch=771.53125-2


It should be noted that the format of the Phase I and Phase II channel grants are identical.
 
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#15
I've never understood what the numbers mean like 1-1364 or 3-1448. There's one under TDMA and another under Ch. Can't make any sense of it. Mine usually start with a 0- instead of a 1-.
 
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#16
I've never understood what the numbers mean like 1-1364 or 3-1448. There's one under TDMA and another under Ch. Can't make any sense of it. Mine usually start with a 0- instead of a 1-.

I don't have any phase 2 by me, but it looks straight forward:

1-1364 control
1-1376 secondary control
1-1404 secondary control
1-1420 secondary control

Voice channel 1-1448 771.05625 and 3-1448 and 3-1449 are the two time slots for that frequency.

P25 phase 2= 2 slot TDMA
 
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#17
Yes, but what does "1-1364" mean? "1-" = one what? One site? One system? and the 1364. Is that one thousand, three hundred, sixty-four of something?
 

AM909

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#19
Yes, but what does "1-1364" mean? "1-" = one what? One site? One system? and the 1364. Is that one thousand, three hundred, sixty-four of something?
Look for the IDEN_UP* messages in the DSDPlus.log file. Here's the map being sent by a local system:
Code:
IDEN_UP		ID=0  Base=851.00625 Offset=-45 Spacing=6.25 BW=12.5
IDEN_UP		ID=1  Base=762.00625 Offset=+30 Spacing=6.25 BW=12.5
IDEN_UP_TDMA	ID=2  Base=851.01250 Offset=-45 Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_TDMA	ID=3  Base=762.00625 Offset=+30 Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_VU	ID=4  Base=450.00625 Offset=+5  Spacing=6.25 BW=12.5
IDEN_UP_VU	ID=5  Base=470.00625 Offset=+3  Spacing=6.25 BW=12.5
IDEN_UP_VU	ID=6  Base=476.00625 Offset=+3  Spacing=6.25 BW=12.5
IDEN_UP_VU	ID=7  Base=482.00625 Offset=+3  Spacing=6.25 BW=12.5
IDEN_UP_VU	ID=8  Base=506.00625 Offset=+3  Spacing=6.25 BW=12.5
IDEN_UP_TDMA	ID=9  Base=450.01250 Offset=+5  Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_TDMA	ID=10 Base=470.01250 Offset=+3  Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_TDMA	ID=11 Base=476.01250 Offset=+3  Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_TDMA	ID=12 Base=482.01250 Offset=+3  Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_TDMA	ID=13 Base=506.01250 Offset=+3  Spacing=12.5 BW=12.5 Slots=2
* ID is the map ID, corresponding to the left side of the channel number (the 1 in 1-1364).
* Base is the mobile's receive frequency (in MHz) of channel 0 of this particular map ID.
* Offset is the default offset of the mobile's transmit frequency from its receive frequency.
* Spacing/Slots is the frequency difference (in kHz) between channels (Slots=1 if not specified)
* BW is the bandwidth of the RF channel

Example 1: To calculate the frequency of channel 1-1364 on this system, look for the line for ID=1:
Code:
IDEN_UP		ID=1  Base=762.00625 Offset=+30 Spacing=6.25 BW=12.5
Mobile RX frequency = Base + (Channel * (Spacing / Slots)) = 762.00625 + (1364 * (0.00625 / 1)) = 770.53125
Mobile TX frequency = 800.53125

Example 2: To calculate the frequency of channel 3-1630 on this system, look for the line for ID=3:
Code:
IDEN_UP_TDMA	ID=3  Base=762.00625 Offset=+30 Spacing=12.5 BW=12.5 Slots=2
Mobile RX frequency = Base + (Channel * (Spacing / Slots)) = 762.00625 + (1630 * (0.0125 / 2)) = 772.19375
Mobile TX frequency = 802.19375
 
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