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Motorola trunking system

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alok

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Joined
Sep 1, 2009
Messages
38
As I tune across some VHF & UHF business frequencies I hear this rapid fire machine gun sound ,it sounds like the samples I hear of the Motorola Trunked System.
I do not have a scanner that will follow trunked systems yet but I am curious , what exactly is this "sound I hear doing" ... is this strictly the data portion of the trunked system ?
If it is where are the voices on a different frequency or frequencies or digital mixed in this machine gun sound ?

I also heard a frequency in my area that has a bunch of different voices / conversations ,but no machine gun noises , what is this ?
One voice group was encrypted ,with a high pitch unable to understand voice.
What kind of system was this and what kind of encryption this was ?

Was this maybe where the voices were of the machine gun frequency I heard ?

Al
 

RKG

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Joined
May 23, 2005
Messages
1,087
Speaking very generally, the described sound is digital data encoded on an RF emission. There are different ways of doing this (e.g., AFSK, FSK, C4FM), though distinguishing amongst them by ear is problematic.

On a Motorola 3600 baud system (a/k/a SmartNet, SmartZone, "Type II"), you might be hearing data over the control channel, or you might be hearing digital voice over any voice channels set up for CAI voice. On a Motorola 9600 baud system (a/k/a AstroTrunking, includes both "Phase 1 and Phase 2), both control channel data and all voice are digitized.

Encryption, if employed, does not change the mode by which digital values are RF encoded; encryption just hashes (think of it as scrambling) the order in which bits are sent.

As I said, foregoing is very general.
 

jim202

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Joined
Mar 7, 2002
Messages
2,558
Location
New Orleans region
As I tune across some VHF & UHF business frequencies I hear this rapid fire machine gun sound ,it sounds like the samples I hear of the Motorola Trunked System.
I do not have a scanner that will follow trunked systems yet but I am curious , what exactly is this "sound I hear doing" ... is this strictly the data portion of the trunked system ?
If it is where are the voices on a different frequency or frequencies or digital mixed in this machine gun sound ?

I also heard a frequency in my area that has a bunch of different voices / conversations ,but no machine gun noises , what is this ?
One voice group was encrypted ,with a high pitch unable to understand voice.
What kind of system was this and what kind of encryption this was ?

Was this maybe where the voices were of the machine gun frequency I heard ?

Al
With your being new to the group here and new to monitoring with a scanner it sure would help in trying to provide answers to your questions if you would provide the needed details.

First of all, It would help to know where your at in the country. This provides the information that let people on here look at the FCC database and try to identify what the frequencies re your talking about.

There are some real good information on just how trunking system works, but it would help to know what type of a system your trying to listen to. Yes the trunking systems for the most part have a control channel that has a constant data flow. The information on this data channel contains a bunch of information. The exact information and where it is in the data stream will vary with the type of trunking system.

In the data stream you will find the system ID. In many cases, it may contain adjacent tower site control channel information. When a user keys up, the control channel will tell all the radios on that talkgroup what voice channel to switch. You will also have the radio user ID of the radio that keyed up.

Some scanners can decode some or all of this information. They, in many cases can be programmed to follow the talkgroup to the assigned to the conversation. The real problem comes up if the system is digital. Not all the scanners out there can do digital trunking systems.

Hope this gives you some of the basics on a trunking systems.

Again, if your looking for answers on a specific frequency, you need to provide the additional information to provide the help.

.
 
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