PSR-500 LTR Mapping feature...

[b52hbuff]

I was reading the o/m regarding the new LTR mapping feature. It didn't really provide much details. Can someone provide answers to the questions below?

1. What does the radio use to sort out the frequencies? Does it only use the home repeater identification? Or does it also use voice transmissions on the home repeater?

2. Many LTR systems aren't licenses properly. They are often IG, and only a subset of frequencies are used in the TRS. So let's say I have a target I'm monitoring, and it shows 10 licenses, but only a few of them are in the LTR system. How can you determine if a frequency has been 'unsorted'?

Thanks!

 

[DaveIN]

1. I would say the home repeater data, but that's a guess based on the previous PRO-97/2055 feature.

2. Interesting, but if the frequencies are licensed for that call sign the FCC tower data should show the frequencies in use, so the radio should sort them when they are used.

 

[pro92b]

Page 120 of the manual indicates that the radio does recognize GOTO and FREE bits in the LTR data stream. By extracting the GOTO bits on any transmission, whether on the home repeater or not, the LCN can be determined for that repeater. This is a major enhancement over the hit and miss PRO-97 method.

It isn't clear from the manual how the radio tags a frequency once it is LCN sorted. Maybe something is set in the TSYS parameters. If a LTR system is already mapped the manual says the frequencies should be entered in LCN order so there must be some indication of LCN on the display so you know that you've done this part right.

It would be interesting to see how the radio would handle sorting a group of frequencies that are actually part of two systems if there are LCN's that are duplicated. Would it display an error if two frequencies are analyzed to the same LCN? Or would it keep the last one received in the LCN lineup and discard the previous frequency?

 

[DaveIN]

Actually page 120 is the control channel dump method to the PC/IF, but it may be how the LCN is determined as you pointed out.

The way I read it, you should be able to enter all the frequencies in any order, then select LCN auto sort, and the radio will re-order to the correct home repeater order. If you were to enter frequencies from another system the radio should error for a duplicate LCN position if it happens to be the same, but that's what we need to verify.

 

[WayneH]

I haven't tried the auto-sort thing yet but here's a sample of the PC/IF Dump for LTR:

LTR:T0055:12: 0-10-12-026-09:Call:TGID-0-12-026 VC- 489.387500
LTR:T0055:12: 0-12-12-129-17:Call:TGID-0-12-129 VC- 490.012500
LTR:T0055:12: 0-10-12-026-09:Call:TGID-0-12-026 VC- 489.387500
LTR:T0055:12: 0-10-12-026-17:Call:TGID-0-12-026 VC- 489.387500
LTR:T0055:12: 0-12-12-129-09:Call:TGID-0-12-129 VC- 490.012500
LTR:T0055:12: 0-10-12-026-17:Call:TGID-0-12-026 VC- 489.387500
LTR:T0055:12: 0-10-12-026-09:Call:TGID-0-12-026 VC- 489.387500
LTR:T0055:12: 0-12-12-129-17:Call:TGID-0-12-129 VC- 490.012500
LTR:T0055:12: 0-31-12-129-12:TurnOff

T#### is the system's object ID in hex, next is the channel where the freq is programmed in, the area bit, the LCN for the GOTO, the group's home LCN, the actual group ID and then the available GOTO LCNs.

 

[DaveNF2G]

Unless you're receiving skip, a frequency that is used in more than one system at close range should show the alternate Area number. I would expect the scanner to distinguish between an Area 0 system and an Area 1 system even if the frequencies overlap.

 

[n4jri]

The biggest problem that I see with LTR systems is that a communications vendor may have more licenses than he does systems, and you can't tell which systems get what frequencies.

Here in Richmond, for example, Commontronics has four different licenses. Viewed separately, they all have random-looking LCN's. Viewed together, they look like they could all be part of the same overall system.

I set up 5 TSYS objects (and corresponding wildcards) for my experiment. The first four systems were the separate licenses. The fifth system was a consolidation of all four licenses. For each system, frequencies were entered in the opposite order of known LCN's. After a few hours of scanning, all but one frequency had been reordered to its proper spot--and I don't know that any transmission had ever been received on that one oddball frequency.

Another problem that I've seen in SMR-type businesses is that frequencies in the same system may be on different licenses to what seem like different licensees. This is going to be your toughest problem since you still have to know what frequencies to enter into the TSYS. It can't go and find them for you.

Bottom line: IF YOU KNOW THE FREQUENCIES, the radio will order them. I don't think you'll have much problem with duplicate frequencies. But the search for missing frequencies, coupled anomalies in the licensing data could cause you to have duplicate LCN's but no clear answer as to which frequency belongs in your target system and which freq is from a different system.

That's a problem no matter what scanner you're using.

73/Allen (N4JRI)

 

[slicerwizard]

Unless you're receiving skip, a frequency that is used in more than one system at close range should show the alternate Area number. I would expect the scanner to distinguish between an Area 0 system and an Area 1 system even if the frequencies overlap.

They were discussing duplicate/reused LCN's, not duplicate frequencies.

 

[slicerwizard]

By extracting the GOTO bits on any transmission, whether on the home repeater or not, the LCN can be determined for that repeater.

Not so. Is this LCN 10 or 15?

0-10-15-123-20

 

[DaveNF2G]

They were discussing duplicate/reused LCN's, not duplicate frequencies.

If an LCN is being reused in the same band by the same licensee, then the systems should still be programmed with alternate Area numbers.

I say "should" because there are some strangely configured LTR systems out there. :twisted:

 

[DonS]

By extracting the GOTO bits on any transmission, whether on the home repeater or not, the LCN can be determined for that repeater.

Not so. Is this LCN 10 or 15?

0-10-15-123-20

Based on my understanding of LTR, the "not so" sounds correct. You could hear such a message on either repeater 10 or 15.

You'd likely have to look at both the "HR" and "Goto" bits. If they're the same, the message can only be heard on the "real" repeater #. The radio could then do the "move" based on that: if "HR" and "Goto" bits in the message are the same, but "HR" doesn't match the currently tuned/programmed LCN/HR#, then move TSYS frequencies around.

 

[pro92b]

I would interpret 0-10-15-123-20 as an area 0 system with ID 15-123 transmitting on repeater number 10. Repeater number 20 is free. It is true that the same message is transmitted on the home repeater as well as the repeater in use. If the home repeater and goto repeater numbers are the same, the transmission is on the home repeater.

 

[DonS]

I would interpret 0-10-15-123-20 as an area 0 system with ID 15-123 transmitting on repeater number 10. Repeater number 20 is free. It is true that the same message is transmitted on the home repeater as well as the repeater in use. If the home repeater and goto repeater numbers are the same, the transmission is on the home repeater.

Yes.

There are at least two more possibilities:

0-10-15-123-20
0-12-15-121-20
0-10-15-123-20
0-12-15-121-20
0-10-15-123-20
means you're tuned to repeater 15.

0-10-15-123-20
0-11-10-120-20
0-10-15-123-20
0-11-10-120-20
0-10-15-123-20
means you're tuned to repeater 10.

(All presuming you're only hearing messages from a single LTR system)

 

[pro92b]

If an LCN is being reused in the same band by the same licensee, then the systems should still be programmed with alternate Area numbers.

I say "should" because there are some strangely configured LTR systems out there. :twisted:

Yes, a single communications company should use the area bits in the case you described. However on the UHF band signals can travel a long way. I can receive systems from the capital district even though I am 50 miles south. Some frequencies active here are also in use in the captial district and the LCN's often do not match. All sorts of confusing combinations are possible.

 

[slicerwizard]

You'd likely have to look at both the "HR" and "Goto" bits. If they're the same, the message can only be heard on the "real" repeater #. The radio could then do the "move" based on tha

You only need to look at idle and comm end OSW's to determine the LCN's for all active channels:

idle: Area-LCN-LCN-255-LCN

comm end: Area-31-Home-Group-LCN

Every active channel transmits one or both of these.

 

[DonS]

You only need to look at idle and comm end OSW's to determine the LCN's for all active channels:

idle: Area-LCN-LCN-255-LCN

comm end: Area-31-Home-Group-LCN

Every active channel transmits one or both of these.

Yes, when idle.

So it's either transmitting one of those (repeater 'idle'), or messages of the format I described above (repeater carrying traffic). Looking for any such "matches" gives you the LCN immediately.

I note that the 'idle' message does fit my format above: Home and Goto are the same.

 

[slicerwizard]

Non-home channels generally don't transmit idle bursts and the voice traffic messages don't directly identify the LCN.
How would you identify the LCN from 0-10-15-123-20 ?

 

[DonS]

Non-home channels generally don't transmit idle bursts and the voice traffic messages don't directly identify the LCN.
How would you identify the LCN from 0-10-15-123-20 ?

As I said previously, I wouldn't. Insufficient information with just that one message. If (as I also said previously) I also saw another message, for example 0-12-15-121-20, I would identify the 'LCN' as Home Repeater number 15.

 

[slicerwizard]

As I said previously, I wouldn't. Insufficient information with just that one message. If (as I also said previously) I also saw another message, for example 0-12-15-121-20, I would identify the 'LCN' as Home Repeater number 15.

The discussion is about auto LCN detection by scanners, correct? Why would you consider an algorithm that had to analyze multiple OSW's when it can be done using single OSW's? I get the impression that you think it will somehow get the job done faster.

 

[DonS]

The discussion is about auto LCN detection by scanners, correct? Why would you consider an algorithm that had to analyze multiple OSW's when it can be done using single OSW's? I get the impression that you think it will somehow get the job done faster.

I do, presuming "idle" OSWs are only sent when there is no group active on the repeater:

Case 1: HR is "idle". We'll see eventually see messages where Home and Goto fields are the same: the 'idle' message.

Case 2: HR is carrying traffic for a group homed to this repeater. We'll very quickly see messages where Home and Goto fields are the same, e.g. 0-10-10-123-12

Case 3: HR is carrying traffic for a group NOT homed to this repeater. We'll NEVER see 'idle' messages. We'll very quickly see messages where Home and Goto fields are different, e.g. presuming current HR is 10: 0-10-12-123-12.

Case 3a: If, in addition to case 3, any group that IS homed to this repeater is also active, we'll also see messages like (presuming the current HR is 10 and the group is active on HR 13): 0-13-10-120-12.

Case 4: An active transmission ends: We'll see the 'turn off' message and immediately know the HR.

My "case 3a" would seem to let a scanner determine the current "LCN" far faster than waiting around for an 'idle' OSW. On an extremely busy system, where conversations on a given HR are back-to-back, will we ever see the 'idle' OSW?

EDIT: I do acknowledge that on a not-so-busy system cases 1 and 2 would likely dominate.