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Old 01-12-2018, 10:22 PM
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Default PL Codes & AES Encryption

Hello everybody!

I have a question as to whether or not multiple PL or DPL Codes on one conventional frequency can also be encrypted? I've built out a conventional codeplug and we have about 80 Personalities and only 20 frequencies to work with. So far, I've been able to load the keys, create two personalities with the same frequencies but different PL Codes - but when I write the changes to the radios, I can still hear traffic between the two different channels.

Does anybody have an idea as to what I could be doing wrong here or would I just have to program multiple keys to the radio and strap each personality to it's own individual conventional talkgroup and then give each talkgroup it's own encryption key?

I'm using SRX 2200's (APX 6000)
and Motorola APX CPS R.16

Thanks in advance and I hope all of you guys had a wonderful holiday season with your family!
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Old 01-13-2018, 7:12 AM
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They can use the same key, but that key has to be selected in both personalities. Your personalities will have to be set to Mixed Mode as well if you want to use AES. In the clear you will have your PL but when you go secure, the radio will revert to P25 mode.
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Old 01-13-2018, 8:10 AM
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If you are running AES encryption, that implies P25 mode? If so, PL tones are irrelevant. PL is only relevant to analog/mixed. Try different NAC codes if P25
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Old 01-13-2018, 8:15 AM
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Quote:
Originally Posted by Thunderknight View Post
If you are running AES encryption, that implies P25 mode? If so, PL tones are irrelevant. PL is only relevant to analog/mixed. Try different NAC codes if P25
You can program an APX/SRX or any other Astro Radio for AES (or another algorithm) on an analog channel with PL, but the channel has to be mixed mode and as soon as the secure switch is flipped the radio reverts to P25 TX/RX.

If you were to program the radio for analog encryption like DES-XL you would lose your programmed PL as soon as you went secure as well.
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Old 01-13-2018, 8:20 AM
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I suspect both channels are set to mixed mode with the same NAC and/or squelch set to Digital but with different pl's.

When encryption is used, the radio only looks at the NAC, the squelch setting on digital and the encryption key ID. Since it sees a match, it unmutes. It doesn't check the pl since you are using digital, not analog.

Change your NAC and make sure your digital squelch is set to Normal.
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Old 01-13-2018, 10:29 AM
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Quote:
Originally Posted by Thunderknight View Post
If you are running AES encryption, that implies P25 mode? If so, PL tones are irrelevant. PL is only relevant to analog/mixed. Try different NAC codes if P25
This is exactly what I ended up having to do.

The way my conventional cpg is setup (in a nutshell) is as such:

Personality 1 >

Name Freq NAC . TX Dev

CH 1 . 123.4567 890 2.5/khz
CH 2 . 123.4567 891 2.5/khz

With this configuration, we get the privacy for radios on Ch 1 and Ch 2 but now the issue we have is that when someone is keying on Ch 2.... Ch 1 can't transmit out.

I changed the Squelch Limit to 13 (15 is the max), and then I changed added PL codes with a large amount of spacing between the two channels and it seems to work intermittently,

Ch 1 & 2 can transmit simultaneously but it is intermittent (broken and unreadble).

What am I missing here?
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Old 01-13-2018, 10:30 AM
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Thank you Mike, that's exactly what I had to do. Now the trick is getting two channels with different NAC's to transmit simultaneously on one frequency and maintain privacy.
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Old 01-13-2018, 10:45 AM
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P25 only supports simultaneous transmissions using TDMA which is only available with P25 trunking.

To do what you want to do, you need DMR which supports TDMA.
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Old 01-13-2018, 12:06 PM
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Quote:
Originally Posted by MikeOxlong View Post
P25 only supports simultaneous transmissions using TDMA which is only available with P25 trunking.

To do what you want to do, you need DMR which supports TDMA.


Sounds like he is confused as to why busy channel lockout is being polite and locking out TX.


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Old 01-13-2018, 12:45 PM
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Quote:
Originally Posted by ExpatLMRGuy View Post
Thank you Mike, that's exactly what I had to do. Now the trick is getting two channels with different NAC's to transmit simultaneously on one frequency and maintain privacy.
PL/NAC only give appearance of isolation between users of a shared channel...monitor mode or scanners allow someone to hear those "private" users.
AES adds security, in that if you don't have the key in your receiver, you won't hear the decoded audio.

HOWEVER, RF is still RF. All of the above are FDMA and therefore it is only one transmission at a time on any particular frequency. The PL or NAC only "hides" other users. If they key up at the same time, and their signal is strong enough, they will disrupt or cover the intended user.

PL/NAC is usually used in one of 3 ways:
1) To keep distant (and weak) signals from another user from being heard. These signals are not strong enough to cover the intended user, but will open the squelch.
2) To keep noise, e.g. from computers, from opening the squelch and annoying the user. If the noise is very strong, it can still cover intended transmissions.
3) To allow multiple users to share a single frequency, for example, what we in the US often call a community repeater, or community tone panel. Several users share one repeater, but even with different PLs, only ONE can use it at a time. It's a game of balancing amount of use (time). If each user is only making a couple of transmissions an hour, they can probably share the repeater with limited chance of issue. (And technically, monitoring the channel before transmitting is required in the US).

If your users are all fairly similar signal strengths, one frequency won't fix your problem.

As the other poster said, you need to split the users in time, which is what TDMA (P25 phase 2, or DMR) is for. Or you need more frequencies.
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