Ctcss/DCS Rolling Codes

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btritch

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I entered this in this forum because I'm not sure where it should belong, Feel free to move it if necessary, I couldn't find a better place though...


Most agencies I'm aware have CTCSS or DCS codes in their systems, I am aware how they work and what their purposes are, However, There is one thing I don't understand and I hope someone here can explain it better,

On some codes such as the nationwide H E A R Hospital 155.340 frequency and UPRR 160.320 Frequency and a few others locally I've noted, When an operator keys up, It doesn't show a code at all, It still says searching, However, when another operator keys up, It shows the codes and rolls them, 79.7, 146.2, 107.2, etc.. Why would it roll them like that, Is there not a set code or is this a universal system etc.? I have also noticed that when it does this if you lock it in and save one of them, You only hear parts of the conversation, Just the part where it rolls back to that code, Can anyone tell me why it does this? Is there a reason? Just curiosity, Thanks For Any Help!
 

af5rn

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I don't know about the UPRR, but 155,340 is left to carrier squelch, almost universally. However, the ambulances that use that channel are usually using an agency radio that is programmed for a CTCSS or DCS to match their agency's system. Consequently, they still transmit that tone, even though they have switched over to a non-tone channel. And since multiple agencies usually use that channel, you will see a variety of tone codes.
 

Grog

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If it is rolling (on one transmission), they might not be transmitting a code and the scanner is falsing. I have had that when they were using a DCS but I was in CTCSS mode, and also just false readings with no tone transmitted.
 

btritch

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If it is rolling (on one transmission), they might not be transmitting a code and the scanner is falsing. I have had that when they were using a DCS but I was in CTCSS mode, and also just false readings with no tone transmitted.
That's exactly what it does, Even on the NOAA channels...
 

SAR923

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I've seen rolling codes even on intermod signals. The scanner is trying to decode what it thinks is a code and rolls though each code trying to find it. On things like railroads and hospital frequencies, I just set the mode to FM so I don't have to watch it falsing.
 

kb2vxa

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Excuse me but "rolling code" is a form of encryption. To avoid confusion I suggest you use the correct term, tone search. This is a feature on most scanners and VHF ham rigs so if you don't want to see it searching for codes turn this feature off.
 

Grog

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Ah I see Mr know it all has to show up once again.


What he describes is the codes rolling on his display, sounds like rolling code is a good way to describe it :roll:
 

ecps92

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Grog, Do you ever have a NICE thing to say ? Didn't Think so :(

Warren is correct, as many folks thought the topic was the "Rolling Code Encryption" commonly
associated with Transcrpyt.



Ah I see Mr know it all has to show up once again.


What he describes is the codes rolling on his display, sounds like rolling code is a good way to describe it :roll:
 

jerk

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Ah I see Mr know it all has to show up once again.


What he describes is the codes rolling on his display, sounds like rolling code is a good way to describe it :roll:
I would think "flashing" would be a better way to describe it.
 
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