Mapping LTR Systems

[Schnoor1648]

I am in the Minneapolis-St. Paul Twin Cities Metropolitan area and I am interested in mapping the local LTR systems. I have been reading as much information as I can about determining details of LTR systems. It almost seems as if many or most of the old rules don't necessarily apply any more. For example:

-At one time I seem to recall that 5 frequencies were a minimum for trunked systems. I have actually read about 1 channel LTR systems.

-Frequency order used to often be either in ascending or descending order with respect to Home Channel Number, but now I read that this may also not always be the case.

-If a given licensee has frequencies in both the 450 and 460 sub-bands, is it likely that the 450 frequencies are in one system and the 460 frequencies another system, or does that not usually matter?

-I thought that any given frequency would only be a part of a single system in a certain area, but now I have read were a given frequency can be a part of different systems of the same licensee or even different licensees in the same area.

-I read that owners often space home channels evenly like 1, 5, 9, 13, 17, but now that seems no longer valid.

-When listening to frequencies conventionally, there may have been a transmission every 10 seconds, but now I read that this may also no longer always be the case.

-Apparently callsigns are not always good indicators of what frequencies belong to what system(s).

-I thought at one time that I read that the middle number in the ID is the Home Channel Number. Is that still the case, or is that also outdates?

-Apparently some trunked licensees can be IG or YG in the FCC database.

Anyway, I am looking for some good tips in figuring out my local systems. I have a Uniden Bearcat BC796D. I use the Butel ARC250/785 software. I also have other radios to monitor frequencies conventionally for activility.

What I have done so far is make a list of all frequencies withing about a 25 mile radius that are licensed for trunking. Then I listened to each one conventionally to see if there is the tell-tale burst every 10 seconds. From there I would enter a given frequency into the BC796 and scan it in the ID SEARCH mode. I have determined what I think are the correct Home Channel Numbers for a number of frequencies. What seems to be the stumbling block now is there are a couple of companies that have over 20 channels licensed in the area. Thus I think that they have more than one LTR system in the area. In fact, I suspect the at least one of the companies has 3 or more systems. How can I determine which frequencies go with which systems? For example, say a certain licensee has 463.725, 464.350, and 464.600 that all come up as Home Channel Number 1. How can I determine which other frequencies are part of say System 1, System 2, or System 3 of licensee "A"? One thought I am considering is to pick an active (and hopefully somewhat unique) talkgroups from a given frequency. Then I could program all ten banks in the BC796D with the ARC250 to see if that ID shows up on any other frequencies. Any thought on how likely this is to be accurate? Any other suggestions on how to map these? I do not have an Optocom, PRO-92/2067, or other radios that track LTR. I would just like to be able to accomplish this using the BC796D and Butel ARC250, if this is possible.

 

[ericcarlson]

At one time I seem to recall that 5 frequencies were a minimum for trunked systems. I have actually read about 1 channel LTR systems.

Regular LTR systems can have anywhere from 1 to 20 channels. The 5 frequency thing is an FCC licensing requirement that requires (generally) that in order to license 5 or more 800/900 MHz frequencies the system must be trunked.

Frequency order used to often be either in ascending or descending order with respect to Home Channel Number, but now I read that this may also not always be the case.

Frequency order is completely arbitrary; sometimes it will be in ascending order but this is not at all guaranteed.

If a given licensee has frequencies in both the 450 and 460 sub-bands, is it likely that the 450 frequencies are in one system and the 460 frequencies another system, or does that not usually matter?

This is not at all guaranteed.

I thought that any given frequency would only be a part of a single system in a certain area, but now I have read were a given frequency can be a part of different systems of the same licensee or even different licensees in the same area.

This is possible but unlikely due to inference issues. Frequencies will generally only be re-used so long as the sites are far enough away not to interfere.

I read that owners often space home channels evenly like 1, 5, 9, 13, 17, but now that seems no longer valid.

Some systems, particularly older ones, followed this rule due to hardware limitations of the equipment being used. However, this is certainly not guaranteed to be the case anymore.

When listening to frequencies conventionally, there may have been a transmission every 10 seconds, but now I read that this may also no longer always be the case.

The transmission every 10-seconds sounds like a quick radio key-up and is an LTR idle data burst. Regular LTR systems usually have these at least on the home repeaters, but some systems have the idle bursts disabled.

Apparently callsigns are not always good indicators of what frequencies belong to what system(s).

Yes; use FCC data as a starting point but don't believe it unless you can confirm it yourself.

I thought at one time that I read that the middle number in the ID is the Home Channel Number. Is that still the case, or is that also outdates?

For regular LTR systems, the "middle number" as displayed by LTR-capable trunktracking scanners is always the home repeater. If the system is LTR Multi-Net or LTR Passport scanners will not display any talkgroups. Some systems are hybrid regular LTR and Passport; for these systems your scanner will only display regular LTR talkgroups. The first digit ("area code") will always be the same for all channels in a given system and can only be 0 or 1. If you see one channel with a 0 area code and another with a 1 area code, then you know that these channels are a part of different systems.

Apparently some trunked licensees can be IG or YG in the FCC database.

Again, the FCC database information is not guaranteed to be accurate. You may find LTR systems licensed under IG, YG, YK or any of the 800/900 MHz radio service codes.

I suspect the at least one of the companies has 3 or more systems. How can I determine which frequencies go with which systems? For example, say a certain licensee has 463.725, 464.350, and 464.600 that all come up as Home Channel Number 1. How can I determine which other frequencies are part of say System 1, System 2, or System 3 of licensee "A"? One thought I am considering is to pick an active (and hopefully somewhat unique) talkgroups from a given frequency. Then I could program all ten banks in the BC796D with the ARC250 to see if that ID shows up on any other frequencies. Any thought on how likely this is to be accurate? Any other suggestions on how to map these?

You are on the right path. I suggest you create a log of frequencies and what talkgroups you hear on those frequencies. After you collect data for awhile, it should become apparent what the home channel number is for each frequency. Based on the other channels a given talkgroup shows up on you can assume they are related if the voice traffic is consistent across all channels; so you can begin to group frequencies into systems. Keep in mind that talkgroups will always be on their home repeater unless the home repeater is in use by another talkgroup.

-Eric

 

[funkytones]

if i have just a mash of 6 freqs... all supposidly on a ltr system... how do i find the corrret order of them so i can put them in my scanner correctly? when i listen to one freq i get 0-01-001/004/etc TGs... and another freq i get 0-03-001/etcetc AND 0-06-001/etcetc... are these different systems?

Schnoor1648... i am in the twin cities also... trying to figure out the mystic lake system

 

[BANDIT]

Take one frequency at a time and program it in all 20 channels. Set the bank for LTR, scan and note which channel you get the voice transmissions on and that should be the correct channel to program that freq. Then do the same with the next freq. If its a pretty active system it should not take to long to figure out the correct slots for each freq.

 

[Schnoor1648]

Mystic Frequencies

Funky. what frequencies do you have for Mistake Lake? I will see if I can hear them at my locations

I know about these at Little Six, but they are different than Mystic aren't they?
451.40000000
451.50000000
452.10000000
452.15000000
452.20000000
452.27500000
452.32500000
452.55000000
452.57500000
452.62500000
452.67500000
452.82500000
461.80000000
463.27500000
464.42500000
464.52500000
464.67500000
464.87500000

This is what I found for Mystic:
451.72500000
452.05000000
452.67500000
462.32500000
462.42500000
463.67500000

Are these six the ones that you are referring to and are all six of these trunked?

 

[funkytones]

the six mystic ones are the ones that i am trying to figure out... never tried any of those little six ones...

where in the twin cities are ya? i will be in shakopee all day today workin on this... i'll post later if i can add any information...

 

[Schnoor1648]

LTR Trunking

I am in Rosemount.

 

[funkytones]

Take one frequency at a time and program it in all 20 channels

tried it... but it worked perfectly on all channels when 1-20 was the same freq... voice on it all

 

[Schnoor1648]

LTR Trunking

So does that mean that it isn't LTR after all?

 

[BANDIT]

If you had the freq and bank both set for LTR, I think you should get the voice only on the one channel that would be the correct slot for that freq. Go back to the home page here and on the left of the screen click on trunking information and then click on LTR trunking information. Read up on it.

 

[Schnoor1648]

Mapping LTR Systems and hopefully making headway

I am continuing to map some of the local LTR systems. Today I scanned just one frequency and logged the active IDs heard. The frequency is 452.4375 which is part of Mobile Radio Engineering's LTR system. I suspect that they have several different LTR systems and I am still trying to determine which frequencies are part of each system. This is Home Channel 18 of the system that it is a part of. The other ID's heard, in addition to those with Home Channel 18, included:

-02
-05
-09
-16
-17

So, if I understand this correctly, this system must have at least six channels, and they will be Home Channels 2, 5, 9, 16, 17, & 18. Thus, if I have thirty other channels to this licensee, but only one of them is Home Channel 17, then it must be part of the same system as 452.4375? If this correct reasoning or am I missing something else? Also, if a company has several LTR systems are the IDs likely to be unique on the different systems or could say:

0-18-105

be Bob's Towing on the first system and

John's Courier on the second system?

 

[ericcarlson]

Re: Mapping LTR Systems and hopefully making headway

So, if I understand this correctly, this system must have at least six channels, and they will be Home Channels 2, 5, 9, 16, 17, & 18.

Yes.

Thus, if I have thirty other channels to this licensee, but only one of them is Home Channel 17, then it must be part of the same system as 452.4375?

Yes, assuming all FCC data is accurate.

Also, if a company has several LTR systems are the IDs likely to be unique on the different systems or could say: 0-18-105 be Bob's Towing on the first system and John's Courier on the second system?

They are not guaranteed to be unique.

-Eric

 

[INDY72]

And another throw off- Some LTR systems are NOT liscensed as trunked at all. One prime example is the Adams County, MS E-911 District. This is liscensed as a conventional (PW) system but is in fact an LTR Passport UHF two site system, with sometimes both repeater sites active, and at other times only one of the two being used. Another is the future Buncombe County, NC LTR Passport UHF system. With LTR's it can be very very tricky to not only get the actual usage type correct (LTR Hybrids being the hardest to nail down), but also getting the proper LCN can be a PITA, even worse than nailing down a new EDACS.....

But then again,.. determining how a system is set up is half the fun of any trunking system, especially LTR's.

For example, untill I read Eric's tricks with other scanners, I thought it was impossible to get LCN's with a PRO-92/2067.... But now have an idea to do just that. Will keep you all updated as the experiment continues.

 

[Schnoor1648]

LTR Mapping

I was doing some unattended logging this evening and when I returned to the history log it displayed an ID of:

0-24-060

Does this necessarily mean that this frequency is being used for Passport? Also, if I understand this correctly, even if there is Passport being used on this frequency, it could also still be used for plain old LTR as well.

 

[ericcarlson]

Re: LTR Mapping

I was doing some unattended logging this evening and when I returned to the history log it displayed an ID of:

0-24-060

Does this necessarily mean that this frequency is being used for Passport?

No, this is just a bad ID. LTR does not have robust error detection/correction and bogus IDs will show up on scanners from time to time. Area code (first digit) must be 0 or 1. Home repeater must be 01-20. Talkgroup must be 001-254.

Also, if I understand this correctly, even if there is Passport being used on this frequency, it could also still be used for plain old LTR as well.

Yes.

-Eric

 

[Schnoor1648]

Mapping LTR Systems with a Uniden BC246T

Has anyone here tried mapping LTR systems by using a Uniden Bearcat BC246T? I was thinking that this might be an excellent scanner for mapping LTR systems. You could enter a given frequency as a one channel system with all twenty possible home channel numbers. Then monitor them in the ID SEARCH mode. Then when a given system comes active you will be able to determine what the Home Channel Number is for that frequency.

 

[ericcarlson]

The BC780XLT and similar models are the easiest. I just got a BC246T (yesterday). Because of the dynamic memory design, there is no concept of a "channel number" as with traditional scanners with "banks." You can however step through the channels in manual mode and if a channel you have programmed as LTR becomes active, the BC246T will display the talkgroup ID -- this just indicates the current talkgroup on the channel, not necessarily the home repeater number.

-Eric

 

[W4KRR]

Here is a website with info on mapping an LTR system using a BC246T scanner:

http://home.hvc.rr.com/bpetrow/ltr.htm

Scroll down toward the bottom of the page. It has methods for other Uniden scanners too.