LTR Mapping with RS Pro-97
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Revision as of 12:43, 29 March 2016 by QDP2012 (updated categories)
Some additional comments based on a slightly different approach to Mapping an LTR System: Observations from using a Pro-97 in Colorado. Tedious, but doable.
1. Pro-97 TGID and home LCN reading is useful but is susceptible to noise. Readings taken from a long, strong transmission are valid. Other readings might not be. Noise can cause false TGID display. I've seen brief inaudible blits of LCN 26 or LCN 32 and other nonsense. Logging these TGIDs over many different transmissions will give the picture of what the valid LCN really is. (By logging I mean I'm using a spreadsheet and typing everything I hear so as to be able to correlate things later.)
2. The systems I am finding seem to have the idle strobe enabled. Suspecting this I did a very slow Tune-step search thru the band of interest logging all strobing signals. Band plans have standard channel spacing so stepping to the next valid frequency isn't too hard. Tune (Funct-Tune - up/down arrow) will find the channel. Using the programmed Search function won't (it seems to be deaf and we're trying to confirm presence of a periodic short burst). Sit on the channel for 5 minutes or so to catch any slow-rate strobes. Log the frequencies where strobes are found. If possible, listen awhile and log TGIDs and most revealing of all - the CWID (that's the morse code station identifier) if it is sent. The systems I've seen have the CWID on its own TGID which for the Pro-97 reveals the LCN of the channel by its home channel number as well as the LCN reading in the Pro-97's field.
3. With CWID you can look up the FCC license info for the system. (Or not. I found one channel identifying itself with an invalid, not on record, callsign. Confirmed the ID several times. No record. ) Using the FRN license info, you can then get additional frequencies that might be part of the system. Listen to them to detect activity and LCNs you might have missed the first time thru.
3.5 Without CWID you can use the FCC lookup by frequency to get some candidate companies and their alleged transmitter locations.
4. With the spreadsheet you have a frequency, maybe some TGIDs and words, and a possible owner name for the system and an LCN for that channel.
5. After collecting the freq and probable LCN and owner you can sort the spreadsheet by owner and then by LCN to create a trial map of the system.
6. Then test the trial map by listening on each channel (manual) for awhile logging TGIDs. You should expect to see TGIDs that are homed on that channel. What you are really looking for are the other TGIDs that pop up there due to their home channel being busy. These TGIDs will tell you that there are other LCNs in the system. For example, I have a trial map showing LCN 01, 17 and 18 for a system. If TGID 0-04-004 pops up on channel 01 this tells me that I am missing a frequency that belongs to channel 04.
7. In some cases, there may be frequencies that fit into the LCN map but aren't actually part of the system. It is possible to have a single-channel system that IDs itself as having a certain LCN. It seems to me that the only way to sort this out is to listen to that channel and watch for other non-homed TGIDs showing that this channel is indeed part of a system. (It could take awhile to reach a conclusion)
8. Not all channels of a system will have the same callsign. But they will probably have the same owner.
9. Not all frequencies listed on a license are on the same system. Not all frequencies listed are in use. Sometimes frequencies list to different owners and the active/expired info isn't sufficient to resolve the ambiguity.
10. TGID number is not sufficient to prove that it is the same user on the same system. Chances are pretty good, for instance, that every system has a 0-01-001 TGID. You have to listen to the users and perhaps learn voices, names and background noise or signal characteristics (ping-on-transmit, digital data racket, hum, etc) to be sure it's the same users showing up on the different channels.
11. It's likely that certain "styles" help you sort a system. For instance, CWID being on 0x-255 on each channel vs 0x-253. Or that the even LCNs are used but the odd ones aren't.
12. Figuring out who has what TGID is straightforward enough to a certain level. For instance recognizing a car towing service is simple. Identifying WHICH company it is could be impossible just by listening. It might take field work so as to be at a location that's aired in order to put eyes on the radio user to get the company name.
13. Foreign language skills might be required. Many truck drivers hereabouts only speak Spanish. I can track a little of this. One TGID on a particular system has been entirely in Russian. I can recognise their voices and pickup a name here and there but I can't tell what business they are in. (taxi most likely?)
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