Digital and Analog on the same frequency

[garys]

I'm reposting this from the Uniden V2 thread because I don't think this is related to the firmware update. It's interesting and as Viper43 pointed out, only happens in the 396 and 996 scanners. The earlier Uniden digital scanners don't have this problem.

I have one frequency that is shared by two different PDs. One is digital and one is analog. I'm roughly halfway between the two so I set CTCSS lockout for the tone used by the analog department.

What happens is I get NO audio from the digital system. Any time there is a signal on the frequency I get a buzz that sounds like some sort of encryption. Neither department uses encryption so that's not it. When a analog signal comes in, I catch about the first half second on the 396 before the scanner blocks it, so I think it's the digital system that's causing the problem.

As a test, I put the same frequency with CTCSS lock out in my 796D. That radios receives and processes the digital signal just fine.

If I take turn the CTCSS off, I get the digital and analog audio just fine from both agencies.

Note that with the 996T, you don't have to program this way because you can select digital, analog, or both.

I think that the ultimate solution will be to have the ability to program in NAC codes, but I don't know that Uniden will offer that upgrade in the current generation of DMA scanners. It would be nice if they did, though.

Gary

 

[Bote]

No digital and analog on same channel

I have one frequency that is shared by two different PDs. One is digital and one is analog. I'm roughly halfway between the two so I set CTCSS lockout for the tone used by the analog department.

What happens is I get NO audio from the digital system. Any time there is a signal on the frequency I get a buzz that sounds like some sort of encryption. Neither department uses encryption so that's not it. When a analog signal comes in, I catch about the first half second on the 396 before the scanner blocks it, so I think it's the digital system that's causing the problem.

If I take turn the CTCSS off, I get the digital and analog audio just fine from both agencies.

Note that with the 996T, you don't have to program this way because you can select digital, analog, or both.

Gary

Set the channel containing all the programming info for the desired agency for digital only after setting any coded squelch to NONE. In other words, do not use the PL reject function, as setting the channel to decode only digital transmissions will automatically reject the analog signal, no matter what code they transmit.

By setting the PL reject, you implicitly defeated the digital decode function of the scanner. (I don't know why Uniden set it up this way, but they did and there it is.) It must sample the first several hundred milliseconds of transmission to discover what code is being transmitted in order to decide to reject it, that is why you were hearing those digital bursts like that. It was only doing what you told it to do.

Make the change and report back, please.

 

[UPMan]

The 396 and 996 have always worked this way; if you enter a CTCSS or DCS (or tone search) on a channel, P25 decoding is completely inhibited.

 

[garys]

Set the channel containing all the programming info for the desired agency for digital only after setting any coded squelch to NONE. In other words, do not use the PL reject function, as setting the channel to decode only digital transmissions will automatically reject the analog signal, no matter what code they transmit.

This will work fine for the 996T, but not for the 396T which doesn't have a digital only option. Which is where the problem lies, but it's not that great a problem since I don't usually monitor either system with this scanner.

Gary

 

[garys]

The 396 and 996 have always worked this way; if you enter a CTCSS or DCS (or tone search) on a channel, P25 decoding is completely inhibited.

I understand that now. What I didn't understand was why CTCSS lock out worked as a filter on the 796D, but not the newer scanners. It would be completely fine if the 396 used the same "audio type" logic as the 996 does. It's slightly less sophisticated (which you know) and hence the problem.

I incidentally solved a similar problem on a VHF channel on my 996. For that system, which is conventional, I just copied a bank from my 796D ARC file. That included the same frequency twice, once with CTCSS lock out and once with CTCSS active. Which I should have realized when I built the profile, but didn't.

Anyway, it's a small problem.

Thanksk

Gary

 

[FlashP]

Mixed mode

True P25 radios usually can be programmed to receive both analog and digital on the same channel, both 'squelched' by CTCSS/DCS and NAC respectively. That allows the users to select digital or analog transmission based on which they expect to work better, and the receiving user doesn't have to know ahead of time what the incoming signal will be.

On the scanners, you can't do this, and you have to program two channels - one analog with CTCSS/DCS, and the other "digital only" (996) or "tone lockout" (396). That works for your 'Two Agency' problem, but for 'One Agency, mixed conversation', you have to twiddle the knob back and forth to follow the conversation.

Flash

 

[garys]

True P25 radios usually can be programmed to receive both analog and digital on the same channel, both 'squelched' by CTCSS/DCS and NAC respectively. That allows the users to select digital or analog transmission based on which they expect to work better, and the receiving user doesn't have to know ahead of time what the incoming signal will be.

NAC is fine for the GRE radios, not yet available for the Unidens. That would certainly solve the problem though.

On the scanners, you can't do this, and you have to program two channels - one analog with CTCSS/DCS, and the other "digital only" (996) or "tone lockout" (396). That works for your 'Two Agency' problem, but for 'One Agency, mixed conversation', you have to twiddle the knob back and forth to follow the conversation.

Flash

Doesn't work this way on either DMA scanner. It does work that way on the earlier legacy scanners. If you put in a tone lock out for the 396, digital will not process properly. That's the problem that I originally described. If you put in tone lock out on a 996, the same thing happens IF there is a digital signal on the frequency. Tone lock out works fine for analog only.

See UPman and other comments.

Gary

 

[Bote]

Doesn't work this way on either DMA scanner. It does work that way on the earlier legacy scanners. If you put in a tone lock out for the 396, digital will not process properly. That's the problem that I originally described. If you put in tone lock out on a 996, the same thing happens IF there is a digital signal on the frequency. Tone lock out works fine for analog only.

Gary

The "tone lockout" feature effectively puts the scanner in carrier squelch mode, and then rejects that one tone or DPL code after it samples it long enough to detect it. Everything else analog comes through.

It's too bad that it won't decode digital signals on that same channel, but that's the way it works and why you need to program another channel to receive the digital transmissions on that same channel.