There's plenty of trunk systems out there that have channel one, channel five, channel nine, channel 11, channel 13, you know those kinds of things. The key here is whatever the logical channel number is, is the exact way it needs to be programmed in your radio. So I'm going to say that one more time. The exact way that the channel numbers are laid out in the system is the exact way that it needs to be programmed into your scanner. So if channel one is channel one in the system, it needs to be in channel one of that scanning bank.
So on the older scanners that did LTR you had multiple banks. So let's say you had a bank of in your particular radio. So either channel one would have to be channel one, channel , , , The first number one channel in that bank would be channel logical channel number one.
But I haven't confused you yet. Then uh, then we're doing pretty well. If I did confuse you, let me know. Give me some feedback on the podcast. Let me know where I've lost ya and I'll be sure to, um, to answer your email, let you know. And again, you can always contact me using the contact form at ScannerSchool.
So on those radios that have specific hard coated channels in a memory bank, channel one's got to be in the channel one part of that bank. Again, you know, channel 1, , , If your bank has channels. If your bank would only have 20 channels in each bank than you would have to say, you know, channel 1, 21, 41, 61, that kind of a setup. So that said, you know, channel five would have to go into the fifth channel in the bank and Channel Ten will go on the 10th channel of a bank, so let's say it that way.
So that x channel number in each bank. Hopefully that makes a little bit more easier to understand. On the radios that use like the dynamic memory allocation is what Uniden calls it. You have to set it up in the system and it asks you for the logical channel number when you program that radio, so you don't need to skip a whole bunch.
You just program it in exactly how it is. So channel three, you put the frequency and this case is channel 1. The next channel, channel 3, we put that into is logical channel number three. Okay, so that aside, we need to make sure it's very, very, very, very important that the channel numbers are in exactly logically. That's the key when listening to LTR. So what happens if you don't program it up correctly? Well, what's going to happen is when you're monitoring an LTR system and the trunk channel gives the direction for the radio to go to one of the channel, you'll see that your scanner's going to try to go that channel and if the frequency is incorrect, it just could go right back to the the control channel.
So I keep using this word home channel. What is a home channel? So each talk group on the system can be dedicated to or assigned to a home channel. And like I said, every frequency in this system, it's not really a control channel, it's a shared channel. It does the controlling as a sub tone and then it's also a voice channel. So you could have a pool of talk groups who have home channel five.
So that means the fifth logical channel in the system or logical channel five is that talk groups home channel. You could have a bunch of talk groups who have maybe logical channel nine as their home channel. So those talk groups always listening to channel nine to find out where to go. Okay, so this is where, like I said, it's a little bit different than standardized trunking because it's a little little odd to wrap your head around, right?
So you could have talk groups spread out over the system. All right, so not everybody is in one location looking for the conductor as we talked about in session seven to tell it where to go. There are little tiny conductors I guess on each repeater channel. And those little conductors will tell you either to stay or to go.
Now if it tells you to go, where's it going to tell you to go to? Well, on the LTR standard system is going to tell you to go to the go-to channel, which would be the next channel in line to go to. So it may say, okay, my home channel is channel five, I have to make a call, but channel five is busy well the conductor is going to tell you in the subtone okay, go to channel nine and you go to your go-to channel which is channel nine.
So how are the talk groups on an LTR system set up? Now this takes a little bit of visualization in your head. So what happens is you have a single digit followed by a hyphen or dash followed by two digits, followed by a hyphen or a dash followed by three digits. Okay, so what is that one by two by three digit called. So what you have is you have your first digit, which is a zero or a one, and that's kind of called your area or your area code. So why do you have an area code of zero or one.
We're talking binary here. And what happens is if you have 2 LTR systems that are in close proximity to each other, that might be sharing a frequency, one system will be assigned an area code of zero and another system might be assigned an area code of one, and you typically will not see a talk group of zero on a system. See why Federal agencies have chosen us as their best value technology partner for over 90 years.
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Device Services. Infrastructure Services. This data burst is not sent at the same time by all the channels, but happens randomly throughout all the system channels.
None of the other LTR types can be decoded or trunked on any scanner. There are a few applications that can be used to gather data, and in some cases decode them.
See our Trunked Radio Decoders article for more information. LTR Standard systems have no dedicated control channel. All control data is sent as subaudible data along with voice transmissions. Systems can have any number of channels from 1 through a maximum of Each channel in the system is assigned a unique number 01 through 20 and these need not be sequentially assigned.
Each subscriber radio must be programmed with all channels in the system in proper logical channel order the same requirement as EDACS systems. With LTR radio systems, hang time is not used for dispatch mobile-to-mobile calls. A channel is held for only the length of the transmission so that the time between transmissions can be used by others making calls.
The only time that hang time is used with LTR trunking is when making telephone calls. Some other trunking methods do use hang time with dispatch calls during heavy loading periods. This allows a called party to almost always respond to a call without being blocked. However, the disadvantages of hang time usage at the system level are significant because it adds directly to the average transmission time which increases blocking and waiting times for others.
However, Figure 3 shows that an LTR distributed system has only about 0. Access priority determines who gains access to a busy system. The method used by most systems with a dedicated control channel is to allow all mobiles to attempt access to the system but deny access to lower priority mobiles by not providing a channel to use.
This means that lower priority mobiles still busy up the system with their access attempts even though they are not given a channel for voice communications. With distributed LTR systems , no mobiles can even attempt to access the system until a channel is available. The mobile that then acquires the channel is the one that makes the first access attempt. This is a first-come-first-served method of access. All mobiles have equal access priority. Operation of an LTR transceiver is even simpler than with conventional operation.
The reason is that many functions normally performed by the user are performed by the control logic such as channel selection and monitoring before transmitting. All the user has to do to make a call is select the desired system and group if applicable and press the push-to-talk switch. If a busy signal or out-of-range condition is not indicated by special tones or warning messages in some displays, the path is complete and speaking can begin.
The basic transceiver controls include power on-off, volume control and system select. Most transceivers also have a group select switch. There is no squelch control because the squelch is internally preset.
Repeaters operate on a single frequency, so one repeater is required for each channel. A controller card in each repeater performs all control and signaling functions on that channel. Information is exchanged between repeaters via a high-speed data bus. A separate system controller is not required.
All mobiles have one of the site repeaters assigned as its "home" repeater. This is the repeater from which it receives most of its control information. When a mobile is not placing or receiving a call, it is always monitoring its home repeater to determine which channel is free and if it is being called by another mobile. The home repeater is always used to make a call unless it is busy.
If the home repeater is busy, any other repeater in the site may be used. Up to ID codes are assigned to each repeater. An ID code and home repeater number are the "address" of mobiles in the system.
Therefore, up to separate addresses can be assigned in a five-repeater system and up to can be assigned in a twenty-repeater system.
An ID code may be assigned to an individual mobile or group of mobiles as required. System control is accomplished by the exchange of data messages between the mobile and repeater. This data signaling occurs continuously with voice at the subaudible frequency of Hz. This eliminates the need for a dedicated control channel and all channels can be used for voice communications for maximum system efficiency.
If a repeater should fail, the rest of the repeaters remain operational. Constant update messages are transmitted by repeaters that are in use so that if a transceiver is just coming into service, a message in progress is not missed.
These messages also inform the mobiles as to which repeater is available. Mobiles can transmit and receive only the ID codes programmed by the system operator. Therefore, other users cannot eavesdrop on the conversations of others. Although traffic can be monitored by a non- LTR transceiver, even that may be difficult because a complete conversation may occur on several channels as described in section 4.
When a mobile makes a call, a data "handshake" occurs with the repeater. The mobile transmits a service request to the repeater and when the repeater detects that message, it transmits a message back to the mobile that tells the mobile that it has successfully accessed the system.
The total time that is required to complete the handshake is less than 0. Other advantages of this handshake are that it insures that the handshake is not occurring on the wrong channel because of intermodulation, and it prevents a mobile with a stronger signal from capturing a channel already in use.
With standard mobile-to-mobile calls, a repeater is held for only the duration of a transmission. This type of trunking is called transmission trunking. With RIC Interconnect calls, the repeater is held for the duration of the call so that a call is not interrupted. Transmission trunking provides maximum system efficiency because others can use the time between transmissions. Refer to section 2.
Data messages are continuously transmitted to the repeater by the calling mobile while a conversation is in progress. The repeater is also continuously transmitting messages to the called mobile and al other mobiles monitoring that channel. The specific information contained in the data messages depends on whether it is repeater or mobile transmitted. The width of each data bit is 3. A complete data message is transmitted in about milliseconds.
The information contained in the various data messages is shown in Figure 6. The information that follows describes the various parts of these messages. The other sync bits are used to detect the arrival of the data message and establish bit synchronization. If the area of the transmitted message does not agree with the programmed area, the message is ignored and the call attempt is unsuccessful. This bit is usually coded "0" unless there are two LTR systems close enough to interfere with each other.
It is then coded "0" in one system and "1" in the other. Mobile-to-Repeater Data Message. If these bits are not the same as the number assigned to the repeater, the message is appearing on the wrong channel because of intermodulation and is ignored. When the PTT switch is released, the transmitter remains on for a short time and the turn-off code 31 is sent in this slot. The code is retransmitted by the repeater and when it is detected by the receiving mobiles, they squelch and resume monitoring the home channel.
This prevents a "squelch tail" noise burst when the transmitting mobile unkeys. With repeater-to-mobile messages, the specific information in this slot depends on whether or not the repeater is busy. If it is busy, separate messages are transmitted to the mobile using the repeater and also to other mobiles that may be trunked out to other repeaters. In the message to the mobile using the channel, this slot contains the repeater number.
In messages to mobiles trunked out to other repeaters, it contains the repeater to switch to in order to receive the call. If the repeater is not busy, a message is transmitted every 10 seconds to keep the mobiles updated and this slot contains the number of the repeater.
This is always the home repeater number programmed into the selected system of the mobile making the call. In a repeater-to-mobile data message, this slot contains the same repeater number received in the data message from the mobile. If the repeater is not busy, it transmits its number in this slot. In a repeater to mobile data message, this is the ID code of the mobile or group of mobiles being called on that channel.
If other mobiles assigned to that repeater have been trunked to other repeaters to receive a call, additional messages are transmitted containing the ID codes of these mobiles. The repeater gets this information from the repeater data bus. The GO-TO information described earlier tells these mobiles which repeater to switch to. In a repeater to mobile data message, this slot contains the number of a repeater that is not busy and available for service.
This tells mobiles assigned to that repeater which repeater to use to make the call. The free repeater is chosen in a random manner as described in section 5. If a repeater is not busy, this slot contains its number. If all repeaters are busy, this slot contains "0". If an error is detected, the message is ignored. There are 21 time slots on the data bas with used for repeater reporting and 21 used by the ID Validator see section 5.
The time slot used by a repeater is determined by the number assigned to that repeater by programming. Repeater 1 uses time slot 1; repeater 5 uses time slot 5 and so on. The data rate on the repeater data bus is 18, bits per second. In its time slot, each repeater places information on the bus indicating its status.
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