NAC Tones

[wlmr]

Played with the chart posted earlier in this thread. My guess is that someone was looking at analog sub-audible tones and wanted a way to decide which NAC code to recommend.

Just tried something with a few of the tones. If you enter the tone into a calculator as a decimal number with no decimal points (100.0 entered as 1000, etc) and convert to hex number you'll get 3E8. It's worked with the small sample of tones I've tried. I suspect that's how the chart came into being, people wanted to know what to program in their newfangled digital radios and this gave them a consistent conversion technique from their older analog PL tones.

I don't think there is a rule dictating this. Frequencies are dictated in a license, are the tones?

When converting to digital, people could have just as easily started over and used NAC 001, 002, 003, etc., or started in the middle and jumped by an arbitrary amount, or (use your imagination here).

Guess along with other guidelines which have been abandoned, if you come across a system that before used specific analog tones, TRY the chart first (or do the math if you can't find the chart). DON'T rely on it

 

[n1das]

Played with the chart posted earlier in this thread. My guess is that someone was looking at analog sub-audible tones and wanted a way to decide which NAC code to recommend.

Just tried something with a few of the tones. If you enter the tone into a calculator as a decimal number with no decimal points (100.0 entered as 1000, etc) and convert to hex number you'll get 3E8. It's worked with the small sample of tones I've tried. I suspect that's how the chart came into being, people wanted to know what to program in their newfangled digital radios and this gave them a consistent conversion technique from their older analog PL tones.

This is EXACTLY how the chart came into being.

I have a ham repeater in the 440 band and it uses a PL of 141.3Hz. I may someday make it into a P25 capable repeater and I plan to use NAC 585 per the chart if I don't use the default NAC of 293.

I don't think there is a rule dictating this. Frequencies are dictated in a license, are the tones?

The radio frequencies to be transmitted on and modulation type(s) on those frequencies are specified in the FCC license. Tones and/or codes for selective calling systems are not specified since they aren't part of what's licensed (the radio frequency). Selective calling tones and codes sort of are specified only in a very indirect way in that they still have to be compatible with the modulation type(s), bandwidth(s), and FCC rules for the particular radio service. Beyond that, the FCC doesn't care what particular PL tone or NAC code each individual licensee uses.

When converting to digital, people could have just as easily started over and used NAC 001, 002, 003, etc., or started in the middle and jumped by an arbitrary amount, or (use your imagination here).

Guess along with other guidelines which have been abandoned, if you come across a system that before used specific analog tones, TRY the chart first (or do the math if you can't find the chart). DON'T rely on it

You got it! If you're setting up a P25 system and are drawing a blank on what P25 NAC code to use, the chart is meant to give you a starting point if you already have a favorite PL tone or DPL code you like to use on analog channels. Don't rely on the chart but at least you can use it as a starting point to help choose a NAC that's easy to remember. (It's not totally meaningless!)

Good luck.

 

[N_Jay]

The chart is a LITTLE more important that that.

As channels are converted to P25, it assures that users who are sharing the channels and using different PLs/DPLs to separate their communications will continue to have the same protection.

BTW, PLs, DPLs and NACS are often issues, or at least recommended and/or approved by the frequency coordinator.

 

[n1das]

What N_Jay said! <lol><cool>

 

[HM1529]

I've noticed that FBI went from an analog PL of 167.9 to a NAC of 167 and DEA went from an analog PL of 156.7 to a NAC of 156. Somebody better tell their radio techs that they didn't follow the "official conversion chart" like "most federal agencies".

 

[N_Jay]

I've noticed that FBI went from an analog PL of 167.9 to a NAC of 167 and DEA went from an analog PL of 156.7 to a NAC of 156. Somebody better tell their radio techs that they didn't follow the "official conversion chart" like "most federal agencies".

Don't worry, they know what they are doing.

Besides they could have converted before the cart was done, or they may be doing other system restructuring.

 

[wlmr]

I've noticed that FBI went from an analog PL of 167.9 to a NAC of 167 and DEA went from an analog PL of 156.7 to a NAC of 156. Somebody better tell their radio techs that they didn't follow the "official conversion chart" like "most federal agencies".

To quote a line from Pirates of the Caribean (spelling?)

"The code's not not exactly a rule, more of a guideline."

 

[ElroyJetson]

When I said only a SUITABLY equipped service monitor would decode NACs, I was referring only to service monitors, of course. An R2010 or R2001 or R2600 won't do it because they're pre-P25 and don't have the option. (Not sure about newer 2600s, though the 2625 will do it.) Other equipment can obviously decode a NAC but I wasn't referring to them and nobody should have assumed I was.

Elroy

 

[RKG]

You are correct, they cannot be used with digital modulation, but there are similar three digits codes which are NAC Codes. I am just wondering if they're the same set as digital pl... such as: 023, 125, 306 ect. Any help would... help.

They are not like DPLs, which are three-digit octal numbers. (Actually, DPLs are 4-digit octals, with a fixed first digit of four.) DPLs are selected so that their equivalent binary strings are distinct.

NACs are simply 3-digit hexadecimal numbers, and their only significance is their hexadecimal values. As a result, except for NACs with a reserved function (pointed out above), a system administrator is free to select any NAC he wishes, arbitrarily.

 

[RKG]

The PSR-500 decodes NAC's just fine. It's a lot cheaper then a service moniotor too and the conversion is not useless it's good information and it works. Most agencies use the converted NAC from their old CTCSS tone. Not all the time but generally. Even the 700MHZ mutual aid frequencies will use a conversion of the current 800MHz Mutual Aids CTCSS of 156.7 which makes it $61F

If you don't beleive it surf the net for about and hour and you'll find 100's of documents supporting this.

I believe what Brother Jetson meant was that the conversion chart could be interpreted as implying some physical, electrical or mathematical relationship between the pairs of PLs and NACs, when in fact there is none. Rather, such charts are arbitrary associations, which are meaningful only insofar as a group of users elects to employ them.

 

[SegmentFault]

In my opinion as well, there is no correllation to NAC/PL/DPL. Its dependant on how the particular repeater or radio is programmed. The NAC code is the digitized version of the analog PL/DPL. In setting up a Mixed Mode Quantar repeater, the user has the ability to set both NAC for Digital and PL/DPL for analog. The reason to do this is in a mixed mode environment, the PL/DPL entry will ensure that the user is not subject to the aweful digital noise during digital repeater operation. With my experience with the XTS5000's that I own and use, the transceiver can be programmed to "Detect Carrier" or PL to ensure that there is nobody being stepped on in either digital or analog mode.

 

[VA3JWO]

can the Uniden bcd396T listen to p25 conventional channels? or do I need to spend the extra mony and get the XT version of the 396?
For Example
Belleville's police use one frequency. Its frequency is 142.035 MHZ and its in p25 mode instead of regular analog mode...
can the 396T listen and decode this channel? or do I need to spend MORE MONEY and get he 396XT

will

 

[BaLa]

can the Uniden bcd396T listen to p25 conventional channels? or do I need to spend the extra mony and get the XT version of the 396?
For Example
Belleville's police use one frequency. Its frequency is 142.035 MHZ and its in p25 mode instead of regular analog mode...
can the 396T listen and decode this channel? or do I need to spend MORE MONEY and get he 396XT

will

Make your own thread next time.


The 396t can decode conventional p25 channels, the XT does also.
But the 396t/xt would be able to decode it.

Did he already ask this in NE forum.

 

[Gezelle007]

For repeaters can you have a different NAC for Input and Output?

 

[ecps92]

Yes, many can and do [many federal agencies]

For repeaters can you have a different NAC for Input and Output?

 

[Cowthief]

Hello.

OK, P-25 NAC codes are,
000 to FFF
There are 16 possible values in Hexadecimal and 3 positions.
But there are some conventions.
As was pointed out, one can set a radio up to open the audio on any valid NAC.
And, a NAC need not be set but is a part of the P-25 protocol, a default will be sent.
Also, one can set some radios up for several NAC, receive and transmit, depends on the vendor product.
NAC has nothing to do with encryption but can be configured to guide the radio as to what key to use, or not, again this is all in the options and how programmed.
Finally, if you can decode P-25 your receiver is dealing with NAC, it is just a question of display.
In fact it should be possible to simply decode the CAI and extract from there, even without the DVSI decoder, this is something I have not tried.
A P-25 radio first sends a fairly straight forward preamble that contains everything needed for the receiver to configure, a new project for someone.