P25 for dummies?

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Token

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All,

I am not at all new to radio, but my monitoring is mostly HF. And when I do VHF and up monitoring it tends to be analog, or it had been until not too long ago. I do have digital scanners, like the Uniden BCD536HP, but I just punch the database into them and let them go. That has worked for what little public service is digital around here.

A few years back the local Navy base moved their local comms from analog VHF FM to P25 on the same (or near same) VHF freqs. Now, I know the guys in the comm shop there, and they told me not only were they P25, but they were encrypted as well, so I never really tried to do any monitoring beyond occasionally tuning across a freq and hearing the digital signal.

But recently, after getting the Icom R8600, I was playing around with the modes and tuned to a couple of those Navy freqs. Whenever a transmission came on the R8600 displayed to me things like "1432 -> 1000 (GRP) NAC:064" and such. I have no idea what that means (OK, I can guess, maybe, source TX, destination group, and some kind of ID). But it was intriguing that occasionally a station would come through with voice also, although most transmissions did not, so at least some of the traffic is not encrypted.

So I need to learn more about P25, but starting at the very basic level.

Can a single node/system carry both encrypted and in-the-clear traffic seemlessly?

Is P25 trunked? Is there a control channel?

Can I learn anything about the system from the displayed information?

What questions don't I know to ask?

Is there a good resource on how P25 works and what things mean aimed at casual listeners out there?

Thanks,

T!
 

UPMan

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All,

Can a single node/system carry both encrypted and in-the-clear traffic seemlessly?
Yes.
Is P25 trunked? Is there a control channel?
Can be trunked or conventional. If trunked, there is a dedicated control channel.
Can I learn anything about the system from the displayed information?
It uses a NAC of 64. NAC is like CTCSS or DCS on analog systems.
 

PrivatelyJeff

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Have you looked the base up on the database? Many places say they are encrypted when in reality they are just digital.
 

pinballwiz86

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Digital P25 systems usually display radio unit ID's. If you keep track of them, you can figure out how many users are on a system.

To get more bang from your BCD536HP I would not "punch" in the database.

Create your own scan list using the Sentinel software. Run a google search to find out how to use Uniden's Sentinel software. This way you are scanning just the stuff you want to hear, and you can create color alerts to label different agencies, saving those radio unit ID's and even label them as well.
 

krokus

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A few years back the local Navy base moved their local comms from analog VHF FM to P25 on the same (or near same) VHF freqs. Now, I know the guys in the comm shop there, and they told me not only were they P25, but they were encrypted as well, so I never really tried to do any monitoring beyond occasionally tuning across a freq and hearing the digital signal.

Not all of the Navy comm techs know LMR as well as they think they do. I had to educate too many of my counterparts, including some that were rather senior, about "Private Line" not being private.

So I need to learn more about P25, but starting at the very basic level.

Can a single node/system carry both encrypted and in-the-clear traffic seemlessly?

Is P25 trunked? Is there a control channel?

Can I learn anything about the system from the displayed information?

What questions don't I know to ask?

P25 can be used for line of sight, repeaters, and trunking. Encryption can be used, like any other digital signal, at the user's discretion.

For a trunked system, there will be a control channel. A Motorola system is the most common, and what the base has, most likely.

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Token

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Have you looked the base up on the database? Many places say they are encrypted when in reality they are just digital.

It is not in the database. And the base specifically went P25 so they could encrypt, the existing analog system handled the traffic just fine but the Navy had a mandate to go digital and the base used the security aspect to justify it to local management.

T!
 

Token

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Not all of the Navy comm techs know LMR as well as they think they do. I had to educate too many of my counterparts, including some that were rather senior, about "Private Line" not being private.



P25 can be used for line of sight, repeaters, and trunking. Encryption can be used, like any other digital signal, at the user's discretion.

For a trunked system, there will be a control channel. A Motorola system is the most common, and what the base has, most likely.

As I said in another post, the base went to P25 specifically so they could encrypt all traffic. I suspect what happened is that originally all units were encrypted, but as new radios have been purchased not all of them have been encrypted. For example I can sometimes hear some some units in the clear and see that they are obviously talking with other units that are encrypted.

I do not think this is trunked, I see no control channel and it appears to be about a dozen freqs in use. I assume I am seeing the repeater outputs as everything is pretty close together to be inputs and outputs. I tend to see specific GRPs or combinations of GRPs on specific freqs.

It was an interesting transition when it all happened. Range activities went digital immediately, Fire went digital a year or so later, and Security (base police) went digital last of all, a couple of years after the system was installed.

T!
 

Token

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Digital P25 systems usually display radio unit ID's. If you keep track of them, you can figure out how many users are on a system.

To get more bang from your BCD536HP I would not "punch" in the database.

Create your own scan list using the Sentinel software. Run a google search to find out how to use Uniden's Sentinel software. This way you are scanning just the stuff you want to hear, and you can create color alerts to label different agencies, saving those radio unit ID's and even label them as well.

I keep meaning to build my own scan list, but really the 536 is mostly the wifes radio. I got it for her a couple years ago to hear local stuff and she is really the one who uses it. For her purposes the database appears adequate. Now that I am starting to look harder at scanner type traffic it is likely I will build a list instead of using the DB. For example, none of the China Lake freqs I have found in the past couple of days are in the DB.

T!
 
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ladn

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Token-another reason you may be hearing clear voice traffic mixed with encrypted is either user error (someone turned off encryption on their radio), or they may be in a weak signal environment where clear voice gets through, but encrypted voice does not. NAWS covers a lot of territory with a plethora of hills and valleys that can make ground level comms difficult.
 

PACNWDude

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That "Private Line" comment made my day. I have seen this as well, even with senior personnel in the Army and Air Force. Explaining CTCSS tones and privacy seems to be lost on many that have used the hardware for a long time.

I was approached by a school a few years back that was being fined for using FRS radios, thinking they were private due to the packaging that said they had "private channels" that could not be monitored. Someone had told them that these blister pack Motorola FRS radios were "encrypted."
 

Project25_MASTR

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P25 can be used for line of sight, repeaters, and trunking.

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That statement is somewhat confusing. P25 can be used for line of sight communications, it can also be used for near line of sight and in some cases, beyond line of sight. Also trunking requires repeaters so that can also lead to some confusion.

I believe what you were trying to get across was P25 can be used in simplex (radio to radio), conventional (using repeaters), and trucked (pools of repeaters) applications.


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kayn1n32008

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Token-another reason you may be hearing clear voice traffic mixed with encrypted is either user error (someone turned off encryption on their radio), or they may be in a weak signal environment where clear voice gets through, but encrypted voice does not. NAWS covers a lot of territory with a plethora of hills and valleys that can make ground level comms difficult.

There is zero range difference between encrypted P25 and un-encrypted P25 transmissions. Its not like in the old days of analogue DES encryption where there was talk out range degradation.

Likely the radios have selective encryption, were a button or switch is used to enable/disable encryption and the user simply has not turned it on.
 
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