ecps92
Member
Or push your state to enhance the $$ Insurance discount since it is a recovery device, not just a theft-deterant
How to decode Lojack?
- Thread starter SCPD
- Start date
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ScannerSK
Member
Good idea!
I checked with my insurance and they would waive the deductible if stolen as I already receive a discount for a theft deterrent. I thought possibly it would pay for itself but in my case such is not the case.
Shawn
ecps92
Member
Off Topic : Insurance Discounts
LoJack - Insurance discount for LoJack® Vehicle Recovery System
Arizona (AZ): Save up to 25%
California (CA): Save up to 33%
Colorado (CO): Save up to 25%
Connecticut (CT): Save up to 25%
Delaware (DE): Save up to 25%
Washington DC (DC): Save up to 25%
Florida (FL): Save up to 25%
Georgia (GA): Save up to 25%
Illinois (IL): Save up to 25%
Louisiana (LA): Save up to 25%
Massachusetts (MA): Save up to 35%
Maryland (MD): Save up to 25%
Michigan (MI): Save up to 25%
New Jersey (NJ): Save up to 25%
Nevada (NV): Save up to 25%
New Hampshire (NH): Save up to 25%
New York (NY): Save up to 25%
Pennsylvania (PA): Save up to 25%
Rhode Island (RI): Save up to 35%
Texas (TX): Save up to 30%
Virginia (VA): Save up to 25%
Florida, Georgia, Massachusetts, New Jersey, New York, Rhode Island, and Texas have mandatory insurance discounts.
For more specific information on LoJack products, visit LoJack.com.
Even if your state is not listed, it does not mean you can’t get an insurance discount, so please check with your insurance company or agent and ask them specifically if you could get a discount for an installed LoJack.
LoJack - Insurance discount for LoJack® Vehicle Recovery System
Arizona (AZ): Save up to 25%
California (CA): Save up to 33%
Colorado (CO): Save up to 25%
Connecticut (CT): Save up to 25%
Delaware (DE): Save up to 25%
Washington DC (DC): Save up to 25%
Florida (FL): Save up to 25%
Georgia (GA): Save up to 25%
Illinois (IL): Save up to 25%
Louisiana (LA): Save up to 25%
Massachusetts (MA): Save up to 35%
Maryland (MD): Save up to 25%
Michigan (MI): Save up to 25%
New Jersey (NJ): Save up to 25%
Nevada (NV): Save up to 25%
New Hampshire (NH): Save up to 25%
New York (NY): Save up to 25%
Pennsylvania (PA): Save up to 25%
Rhode Island (RI): Save up to 35%
Texas (TX): Save up to 30%
Virginia (VA): Save up to 25%
Florida, Georgia, Massachusetts, New Jersey, New York, Rhode Island, and Texas have mandatory insurance discounts.
For more specific information on LoJack products, visit LoJack.com.
Even if your state is not listed, it does not mean you can’t get an insurance discount, so please check with your insurance company or agent and ask them specifically if you could get a discount for an installed LoJack.
ScannerSK
Member
During the tracking of this stolen vehicle this morning there was an unusual side ID which began this morning and ended just prior to the police announcing they had a suspect at gunpoint. If the unusual site IDs are actually the speed-up commands, then a stolen vehicle transponder should be noticed to slow down to a rate of one tracking pulse every 15 seconds about 30 minutes after the last unusual site ID was broadcast.
Shawn
ScannerSK
Member
Denny, I was also thinking about the false reply codes which appear in SDRTrunk on average once a day or once every other day on my end which in the future may set off false alerts. I was wondering if it would be possible to implement something similar to the following to eliminate most of the false reply codes:
If the received function code is E and CRC does not correct the function code then it is a Function E with unknown purpose.
If the received function code is F and CRC does not correct the function code then it is a Function F with unknown purpose.
If the received function code is E and CRC does correct the function code to a Function F then it is a Function F stolen vehicle tracking pulse/reply code.
Just curious...
A second possibly better option may be to only have the program activate the reply code "alert" feature when two identical reply codes are seen to occur back to back (next to each other).
Just thinking of ways to eliminate false reply code "alerts".
Shawn
73s
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ScannerSK
Member
Mystery LoJack System = Colorado LifeTrak System?
I discovered today that about ten miles North of my house I can receive (albeit very weak) one of the mystery system transmissions.
The following are the start and stop times (in minutes and seconds into my recording) when the mystery signals were noted to occur:
10:46-10:49
25:49-25:52
40:52-40:54
55:55-55:57
70:57-71:00
86:00-86:03
101:03-101:05
116:06-116:08
131:08-131:11
146:11-146:14
161:14-161:17
176:17-176:20
191:20-191:22
206:23-206:25
221:25-221:28
So from the above, it appears this mystery system transmits approximately once every 15 minutes and 2.75 seconds.
With additional evidence of a tower closer to home it may motivate me to do a little fox hunting tomorrow and possibly work toward solving this little mystery. Everything (especially the specific areas I have received transmissions from this mystery system) is pointing toward this being the Colorado LifeTrak system (which is located in at least three Colorado counties).
Shawn
73s
I discovered today that about ten miles North of my house I can receive (albeit very weak) one of the mystery system transmissions.
The following are the start and stop times (in minutes and seconds into my recording) when the mystery signals were noted to occur:
10:46-10:49
25:49-25:52
40:52-40:54
55:55-55:57
70:57-71:00
86:00-86:03
101:03-101:05
116:06-116:08
131:08-131:11
146:11-146:14
161:14-161:17
176:17-176:20
191:20-191:22
206:23-206:25
221:25-221:28
So from the above, it appears this mystery system transmits approximately once every 15 minutes and 2.75 seconds.
With additional evidence of a tower closer to home it may motivate me to do a little fox hunting tomorrow and possibly work toward solving this little mystery. Everything (especially the specific areas I have received transmissions from this mystery system) is pointing toward this being the Colorado LifeTrak system (which is located in at least three Colorado counties).
Shawn
73s
Last edited:
ScannerSK
Member
LoJack Full Circle of Events Captured (Function 8=Speed-Up!)
I was able to verify the full circle of events today for one LoJack transponder. It started this morning when Airborne 1 began to receive a LoJack hit before 9:00 AM in the Denver area (presumably around 8:45 AM).
Around noon, I did notice a few tracking pulses however they were extremely faint and off in the distance. At about 1:30 PM, the tracking pulses suddenly became strong in the area of a shopping center. I stopped in a busy store parking lot and monitored the signals for about an hour capturing both slow-down and speed-up events while catching up on a little reading.
In all four of the separate instances in which I noticed the tracking pulses either speed-up or slow down, the data for a specific unusual site ID corresponded precisely in time to all these transitions. When first activated, it appears the transponder is in the slow mode (sending out pulses once every 15 seconds). When the unit begins to be tracked, a Function 8 frame is sent containing a specific address to that transponder which transitions it from the slow mode to the fast mode (pulses sent once every few seconds) for a period of 30 minutes after which time the transponder automatically transitions back to the slow mode. I even captured on recording one outstanding example of a slow tracking pulse which immediately transitioned to a fast tracking pulse at the end of the tower transmission which contained the required unusual site ID to speed up the transponder. The unusual site IDs are definitely the speed-up/tracking command. Unusual site IDs in our data reveal that a vehicle in range of the tower is actively being tracked.
What do I mean by unusual site IDs? In my area there are three towers I receive each minute. The first tower is FA-40 and then 8 seconds later FA-81 and then 8 seconds later FA-80. 64 seconds after FA-40 was last received the process repeats. FA-40, FA-81 and FA-80 are the normal site IDs in my local area. Other site IDs other than FA-40, FA-81 and FA-80 which are seen to occur frequently (not just a single occurrence) are what I am referring to as unusual site IDs. In the normal site IDs the first 3 characters change and the last 4 remain the same in each transmission. However, in the unusual site IDs the entire address remains the same in each transmission.
A side note of interest, I noticed that a speed-up command issued while the transponder is in the fast mode does not add an additional 30 minutes to the fast mode. The speed-up commands appear to only be valid when the transponder is in the slow mode.
During the cycle of events today, I captured in the tower data the time the tower first issued the activation command, a recording of the reply code, four separate verifiable occurrences of speed-ups or slow-downs that corresponded to a specific unusual site ID and the time the tower sent the deactivation command (which occurred precisely at the time I noted when the transmissions ceased). (There were no Function 3 or Function 6 frames during the entire time period.) (The activate commands were falling into both the 7th and 8th frames. The unusual site IDs were falling into the 6th, 7th and 8th frames.)
So what does this mean?
1.) Function 8 frames are the speed-up commands for most if not all LoJack units. Function 8 can be re-labeled in SDRTrunk to "Speed-Up/Site-ID" or similar.
2.) The set rate command may not be used at all or used infrequently as the transponder will automatically transition into the slow mode after 30 minutes.
3.) In SDRTrunk we currently have Function 3 labeled as the "speed-up" and Function 6 labeled as the "set rate". We may consider changing these back to "unknown" until their purpose is understood? Or, possibly they are labeled correctly however only apply to certain older LoJack transponder models?
4.) By comparing unusual site IDs across the country is it possible to verify the approximate block of addresses (presumably just the last four of the address) which are set aside to only be used as tower IDs?
One thing which occurred to me today, which applies to all types of digital radio signals, is that it is possible to audibly hear digital signals on a scanner even before they are capable of being properly decoded. This may potentially mean that a scanner has a couple of advantages: 1.) The ability to know weak signals are present, and 2.) Due to #1, the ability to locate the general area of a signal sooner.
The police did find the exact location of the vehicle. On the scanner it was reported as unoccupied and they were preparing to tow it off the last I heard.
Shawn
73s
I was able to verify the full circle of events today for one LoJack transponder. It started this morning when Airborne 1 began to receive a LoJack hit before 9:00 AM in the Denver area (presumably around 8:45 AM).
Around noon, I did notice a few tracking pulses however they were extremely faint and off in the distance. At about 1:30 PM, the tracking pulses suddenly became strong in the area of a shopping center. I stopped in a busy store parking lot and monitored the signals for about an hour capturing both slow-down and speed-up events while catching up on a little reading.
In all four of the separate instances in which I noticed the tracking pulses either speed-up or slow down, the data for a specific unusual site ID corresponded precisely in time to all these transitions. When first activated, it appears the transponder is in the slow mode (sending out pulses once every 15 seconds). When the unit begins to be tracked, a Function 8 frame is sent containing a specific address to that transponder which transitions it from the slow mode to the fast mode (pulses sent once every few seconds) for a period of 30 minutes after which time the transponder automatically transitions back to the slow mode. I even captured on recording one outstanding example of a slow tracking pulse which immediately transitioned to a fast tracking pulse at the end of the tower transmission which contained the required unusual site ID to speed up the transponder. The unusual site IDs are definitely the speed-up/tracking command. Unusual site IDs in our data reveal that a vehicle in range of the tower is actively being tracked.
What do I mean by unusual site IDs? In my area there are three towers I receive each minute. The first tower is FA-40 and then 8 seconds later FA-81 and then 8 seconds later FA-80. 64 seconds after FA-40 was last received the process repeats. FA-40, FA-81 and FA-80 are the normal site IDs in my local area. Other site IDs other than FA-40, FA-81 and FA-80 which are seen to occur frequently (not just a single occurrence) are what I am referring to as unusual site IDs. In the normal site IDs the first 3 characters change and the last 4 remain the same in each transmission. However, in the unusual site IDs the entire address remains the same in each transmission.
A side note of interest, I noticed that a speed-up command issued while the transponder is in the fast mode does not add an additional 30 minutes to the fast mode. The speed-up commands appear to only be valid when the transponder is in the slow mode.
During the cycle of events today, I captured in the tower data the time the tower first issued the activation command, a recording of the reply code, four separate verifiable occurrences of speed-ups or slow-downs that corresponded to a specific unusual site ID and the time the tower sent the deactivation command (which occurred precisely at the time I noted when the transmissions ceased). (There were no Function 3 or Function 6 frames during the entire time period.) (The activate commands were falling into both the 7th and 8th frames. The unusual site IDs were falling into the 6th, 7th and 8th frames.)
So what does this mean?
1.) Function 8 frames are the speed-up commands for most if not all LoJack units. Function 8 can be re-labeled in SDRTrunk to "Speed-Up/Site-ID" or similar.
2.) The set rate command may not be used at all or used infrequently as the transponder will automatically transition into the slow mode after 30 minutes.
3.) In SDRTrunk we currently have Function 3 labeled as the "speed-up" and Function 6 labeled as the "set rate". We may consider changing these back to "unknown" until their purpose is understood? Or, possibly they are labeled correctly however only apply to certain older LoJack transponder models?
4.) By comparing unusual site IDs across the country is it possible to verify the approximate block of addresses (presumably just the last four of the address) which are set aside to only be used as tower IDs?
One thing which occurred to me today, which applies to all types of digital radio signals, is that it is possible to audibly hear digital signals on a scanner even before they are capable of being properly decoded. This may potentially mean that a scanner has a couple of advantages: 1.) The ability to know weak signals are present, and 2.) Due to #1, the ability to locate the general area of a signal sooner.
The police did find the exact location of the vehicle. On the scanner it was reported as unoccupied and they were preparing to tow it off the last I heard.
Shawn
73s
Last edited:
ScannerSK
Member
SDRTrunk Sound Setting
I discovered I had the recording setting on my computer set in error to "Stereo Mix". For some reason (possibly a feedback loop) this was having the result of bogging down the SDRTrunk program on my computer. After 6-12 hours an increasing delay (over several seconds) was noticed between when the data was received versus when it was decoded and appeared on the screen. Due to this, I was in the habit of restarting the SDRTrunk program several times each day.
This morning, I changed the recording setting to "Microphone" and this completely solved the problem. Just an FYI should anyone else have their recording selection set to "Stereo Mix".
Shawn
I discovered I had the recording setting on my computer set in error to "Stereo Mix". For some reason (possibly a feedback loop) this was having the result of bogging down the SDRTrunk program on my computer. After 6-12 hours an increasing delay (over several seconds) was noticed between when the data was received versus when it was decoded and appeared on the screen. Due to this, I was in the habit of restarting the SDRTrunk program several times each day.
This morning, I changed the recording setting to "Microphone" and this completely solved the problem. Just an FYI should anyone else have their recording selection set to "Stereo Mix".
Shawn
ScannerSK
Member
Data from a member
I received a large data file from a member in Florida. There were over 100 vehicles which appear to have been recovered in the data; I did not count the exact number. However, there was some unusual activity as well.
One address [0134535] shows 801 deactivations between Jan. 2nd and Jan. 23rd. Then after a break in activity from Jan. 18th through Jan. 22nd there is suddenly 53 speed-up (Function 3) frames interspersed with numerous deactivations which is later followed by another 503 deactivations between Jan. 23rd through Jan. 26th. There are no activations noted in the data. Testing?? Very unusual. I have never noticed anything like this in Colorado.
Another address [3E37D82] shows it switched back and forth between activation and deactivation five separate times which is very unusual and may indicate some type of training.
It appears the normal towers for this member in Florida are 76-61, 76-C0, 76-C1 and 76-E0.
Your data appears to indicate the following unusual site IDs (Function 8 speed-up addresses) should anyone be interested:
There were maybe half a dozen speed-up (Function 3) frames which had the same address however nothing unusual.
The set rate (Function 6) frames were a bit interesting. Below is a chart showing the number of frames received and the timeframe in which they were received.
I no longer require any data files. If anyone would like to receive data files from other members for review just ask and I'm sure someone will have data to send your way. Or, if you have data files you would like to share feel free to mention you have them available here and someone may take you up on the offer.
Shawn
I received a large data file from a member in Florida. There were over 100 vehicles which appear to have been recovered in the data; I did not count the exact number. However, there was some unusual activity as well.
One address [0134535] shows 801 deactivations between Jan. 2nd and Jan. 23rd. Then after a break in activity from Jan. 18th through Jan. 22nd there is suddenly 53 speed-up (Function 3) frames interspersed with numerous deactivations which is later followed by another 503 deactivations between Jan. 23rd through Jan. 26th. There are no activations noted in the data. Testing?? Very unusual. I have never noticed anything like this in Colorado.
Another address [3E37D82] shows it switched back and forth between activation and deactivation five separate times which is very unusual and may indicate some type of training.
It appears the normal towers for this member in Florida are 76-61, 76-C0, 76-C1 and 76-E0.
Your data appears to indicate the following unusual site IDs (Function 8 speed-up addresses) should anyone be interested:
Code:
[00-30], [06-C0], [09-87], [0A-E1], [0D-F9], [18-E4], [18-F0], [1B-D0], [24-3F], [2B-E0], [30-19], [32-80], [32-C0], [35-F8], [36-00], [36-61], [36-C0], [36-C4], [3E-7E], [3E-C0], [3F-B1], [40-17], [43-EF], [45-A1], [46-41], [4A-91], [4E-C0], [52-20], [53-21], [56-10], [56-C8], [57-A6], [57-C0], [57-FD], [58-30], [5C-43], [5F-51], [5F-8C], [66-71], [66-8F], [66-C3], [66-E3], [69-47], [69-D0], [6A-E6], [6E-D8], [6F-20], [70-00], [70-2C], [70-40], [70-72], [70-81], [70-B0], [70-E0], [72-01], [72-60], [72-6F], [72-C1], [72-E3], [74-60], [74-61], [74-63], [74-C0], [75-60], [76-00], [76-03], [76-0B], [76-23], [76-41], [76-42], [76-69], [76-70], [76-71], [76-73], [76-80], [76-A1], [76-BF], [76-D8], [76-D9], [76-E8], [76-F0], [77-00], [77-60], [77-8F], [77-E0], [77-E1], [77-F1], [77-F2], [78-C0], [79-36], [79-E0], [7A-50], [7A-60], [7A-C0], [7B-C0], [7B-E0], [7C-00], [7C-01], [7C-30], [7D-70], [7D-D9], [7D-FF], [7E-61], [7E-69], [7F-C0], [7F-E0], [7F-E6], [80-A0], [80-EA], [85-EF], [89-61], [8F-D0], [8F-F4], [90-6A], [93-C0], [93-D1], [94-10], [96-21], [9C-DF], [A0-D1], [A5-00], [A7-31], [A8-20], [A8-60], [AD-F0], [AF-B0], [B6-60], [B6-70], [B7-C0], [B8-20], [BF-22], [BF-D8], [C1-DC], [C5-E3], [C6-3E], [C8-E1], [CD-60], [D8-50], [DC-D0], [DF-FC], [E0-11], [E2-60], [E2-86], [E3-F3], [E9-C6], [EB-3E], [EC-39], [EC-C2], [EF-F4], [EF-FC], [F0-40], [F0-C0], [F0-E0], [F2-40], [F2-A1], [F3-30], [F3-40], [F4-73], [F4-C4], [F5-20], [F6-10], [F6-44], [F6-60], [F6-E0], [F6-E8], [F6-F8], [F7-07], [F7-F0], [F8-7C], [F8-A1], [F9-3B], [FD-85]There were maybe half a dozen speed-up (Function 3) frames which had the same address however nothing unusual.
The set rate (Function 6) frames were a bit interesting. Below is a chart showing the number of frames received and the timeframe in which they were received.
Code:
Quantity Address Timeframe
24 6A7BB30 4 hours
25 7070570 3 hours
102 E32A0B0 23 hours
165 EB47BB0 24 hours
26 F8692B0 6 hoursI no longer require any data files. If anyone would like to receive data files from other members for review just ask and I'm sure someone will have data to send your way. Or, if you have data files you would like to share feel free to mention you have them available here and someone may take you up on the offer.
Shawn
Last edited:
Shawn, I'm updating the sdrtrunk code this evening. I renamed functions 6 and F as Unknown.
Something interesting stands out from the Function bits:
The only function that uses bit position 4 is the 3-speedup command, which you've said you're unsure if that is correct. What if only the first 3 bits represent the function and the 4th bit is some form of flag that can be independently used with any of the other functions.
Another thought - you've observed that function 8 serves two purposes: site id and speedup/slowdown during a transponder activation. What if the weird site id is actually a mix of the normal site id bits with the activated transponder's address, forming a verification value for the transponder to validate that the speed-up command is legitimate. That way, the transponder would only respond to it's own address mixed with at least one of the site identifiers that it has previously/recently heard.
I'm wondering if you can XOR the unusual site id bits with the normal site id bits and produce the activated transponder's address?
From a transponder perspective, any received function 8 messages are first XOR'd with the transponder's own address to see if the remainder matches a site id known to (heard by) the transponder. If not, store the value as a new site id.
And then shooting a hole in this theory ... why would you include validation of the speed-up command and not the activation/deactivation commands. Unless an activation command has to be followed shortly by a validation command, otherwise the transponder considers it a false alarm/activation.
Were there any other changes besides deleting the 6 and F function codes that you wanted changed in sdrtrunk? (and the alerting feature).
Denny
Something interesting stands out from the Function bits:
Code:
001 0 = 2 Activation
001 1 = 3 Speed Up
010 0 = 4 Test
100 0 = 8 Site ID / Speed Up
110 0 = C Deactivate
111 0 = E Tracking PulseThe only function that uses bit position 4 is the 3-speedup command, which you've said you're unsure if that is correct. What if only the first 3 bits represent the function and the 4th bit is some form of flag that can be independently used with any of the other functions.
Another thought - you've observed that function 8 serves two purposes: site id and speedup/slowdown during a transponder activation. What if the weird site id is actually a mix of the normal site id bits with the activated transponder's address, forming a verification value for the transponder to validate that the speed-up command is legitimate. That way, the transponder would only respond to it's own address mixed with at least one of the site identifiers that it has previously/recently heard.
I'm wondering if you can XOR the unusual site id bits with the normal site id bits and produce the activated transponder's address?
From a transponder perspective, any received function 8 messages are first XOR'd with the transponder's own address to see if the remainder matches a site id known to (heard by) the transponder. If not, store the value as a new site id.
And then shooting a hole in this theory ... why would you include validation of the speed-up command and not the activation/deactivation commands. Unless an activation command has to be followed shortly by a validation command, otherwise the transponder considers it a false alarm/activation.
Were there any other changes besides deleting the 6 and F function codes that you wanted changed in sdrtrunk? (and the alerting feature).
Denny
ScannerSK
Member
Hi Denny,
Function F can be left as "F-TRACK PULSE REPLY CODE" as this is what appears in SDRTrunk for tracking pulses (after the CRC corrects the function bits). Function E should be updated to unknown.
Here is my current list of Function codes and their usage:
Function 2: Activation
Function 3: Unknown (only broadcast typically for several minutes) (tower related?)
Function 4: Test
Function 6: Unknown (possible speed-up on older units)
Function 8: Speed-Up/Site IDs
Function C: Deactivation
Function E: Unknown
Function F: Tracking Pulses
You may be onto something about the 4th bit in the function code.
In the normal site IDs the first three characters change with each frame while the last four in the address remain constant (the tower ID). However, in the case of the unusual site IDs all seven characters in the address remain constant with each transmission.
The unusual site IDs don't appear to be a mixture however I have not tried to XOR the activation/deactivation address against a normal site id. Here are a few lines from the full cycle of events captured yesterday showing the first activation, the first speed-up and the deactivation.
Code:
20150128 81553 PASSED FUNCTION: 2-ACTIVATION ADDRESS [39382DE] VRC [C0] LRC [45] CRC [F65F]
20150128 84545 PASSED FUNCTION: 8-SITE ID SITE [4E-21] ADDRESS [2D54E21] VRC [22] LRC [4E] CRC [394F]
20150128 141409 PASSED FUNCTION: C-DEACTIVATE ADDRESS [39382DE] VRC [83] LRC [BA] CRC [7DCB]My normal tower IDs are FA-40, FA-81 and FA-80.
Possibly... I'm not exactly sure how to go about it though as the first three characters change in the normal site id. I posted the above addresses from the full cycle of events which occurred yesterday for you to experiment with.
Possibly...
Let me think.
Function F is the reply code. (Even though Function E is transmitted SDRTrunk updates it to a Function F every time to match the CRC.)
Function E should be unknown.
Function 3 is unknown (typically these are only broadcast for a few minutes) (possibly tower related?)
Function 6 is unknown however does mimic the Function 8 speed-up frames (which sometime skip over blocks of time when a vehicle is not
being tracked) Possibly Function 6 is the speed-up frame for certain older LoJack models?
Function 8 is Speed-Up/Site IDs
Also, would it be possible for the alert not to go off unless two identical reply codes are seen to occur back to back (next to each other)? This should all but eliminate false alerts.
Thank you Denny! I appreciate all you do!
Shawn
73s
Last edited:
ScannerSK
Member
Function 3 thoughts
I awoke thinking about Function 3 this morning. In the LoJack Network Repeater Unit on the FCC website the following is stated: "The NRU fully supports... basic messages such as Activation, Deactivation, Speed up, and extended downlink messages such as AltDeactivate."
I wonder what function if any in SDRTRunk represents the AltDeactivate? I wonder what purpose it serves?
Way back in post #37, I noted the following (functions updated in this post to LSB to prevent confusion):
"Addresses having a function 3 code also appear with a function 2 [Activation] code regularly. About half the time a function 3 code will appear just before an address stops being transmitted by the tower. The rest of the time addresses with function 3 codes transmit occasionally between sets of function 2 [Activation] codes." For some reason after updating SDRTrunk to LSB and turning on the CRC corrections, I do not receive Function 3 activity very often and I have not seen any examples at all of addresses that appeared both as a Function 2 (Activation) and Function 3 which previously was noted as occurring "regularly". I may experiment with an older version of SDRTrunk for a while to see if possibly some of the Function 3 frames are failing the CRC check.
In the data sample from Florida (post #229), Function 3 and Function C (Deactivate) were seen occurring simultaneously. In my post #37, Function 3 and Function 2 (Activation) were seen occurring simultaneously.
I wonder how Function 3 could in one instance occur simultaneous with the Activation command and in another instance occur simultaneously with the Deactivate command? Function 3 is unusual.
My notes on Function 3 are as follows:
1.) They do not match across the country (rather local in nature)
2.) Appear to not be relayed by other towers
3.) Typically only broadcast for several minutes
4.) Seen to occur most often within 2 hours of a deactivation
In my books Function 3 is still unknown.
Function 6 on the other hand mimics the same type of speed-up activity noted to occur for Function 8 speed-up requests. So, possibly Function 6 is also a speed-up for older LoJack units?
Shawn
I awoke thinking about Function 3 this morning. In the LoJack Network Repeater Unit on the FCC website the following is stated: "The NRU fully supports... basic messages such as Activation, Deactivation, Speed up, and extended downlink messages such as AltDeactivate."
I wonder what function if any in SDRTRunk represents the AltDeactivate? I wonder what purpose it serves?
Way back in post #37, I noted the following (functions updated in this post to LSB to prevent confusion):
"Addresses having a function 3 code also appear with a function 2 [Activation] code regularly. About half the time a function 3 code will appear just before an address stops being transmitted by the tower. The rest of the time addresses with function 3 codes transmit occasionally between sets of function 2 [Activation] codes." For some reason after updating SDRTrunk to LSB and turning on the CRC corrections, I do not receive Function 3 activity very often and I have not seen any examples at all of addresses that appeared both as a Function 2 (Activation) and Function 3 which previously was noted as occurring "regularly". I may experiment with an older version of SDRTrunk for a while to see if possibly some of the Function 3 frames are failing the CRC check.
In the data sample from Florida (post #229), Function 3 and Function C (Deactivate) were seen occurring simultaneously. In my post #37, Function 3 and Function 2 (Activation) were seen occurring simultaneously.
I wonder how Function 3 could in one instance occur simultaneous with the Activation command and in another instance occur simultaneously with the Deactivate command? Function 3 is unusual.
My notes on Function 3 are as follows:
1.) They do not match across the country (rather local in nature)
2.) Appear to not be relayed by other towers
3.) Typically only broadcast for several minutes
4.) Seen to occur most often within 2 hours of a deactivation
In my books Function 3 is still unknown.
Function 6 on the other hand mimics the same type of speed-up activity noted to occur for Function 8 speed-up requests. So, possibly Function 6 is also a speed-up for older LoJack units?
Shawn
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ScannerSK
Member
SDRTrunk Tweaks
Denny,
I notice SDRTrunk often does not display all eleven frames in the data burst (sometimes only three or four) even though it is a strong well defined data burst with eleven frames. This may be due in part to my using the audio output on the scanner and the audio input on my computers. I've experimented with multiple things on my end to no avail.
In the tower data burst transmissions I have noticed that the frequencies get off slightly when transitioning between bits. For this reason, I wonder if the 1200/1800 Hz frequencies could be adjusted slightly to obtain a better decode? Possibly 1250/1750 Hz or 1300/1700 Hz?
Just curious... I'm not sure if this would help any or make the decoding worse?
I also plan to look into locating the discriminator tap on the scanner for a cleaner audio signal and possibly build a dedicated interface.
Shawn
Denny,
I notice SDRTrunk often does not display all eleven frames in the data burst (sometimes only three or four) even though it is a strong well defined data burst with eleven frames. This may be due in part to my using the audio output on the scanner and the audio input on my computers. I've experimented with multiple things on my end to no avail.
In the tower data burst transmissions I have noticed that the frequencies get off slightly when transitioning between bits. For this reason, I wonder if the 1200/1800 Hz frequencies could be adjusted slightly to obtain a better decode? Possibly 1250/1750 Hz or 1300/1700 Hz?
Just curious... I'm not sure if this would help any or make the decoding worse?
I also plan to look into locating the discriminator tap on the scanner for a cleaner audio signal and possibly build a dedicated interface.
Shawn
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The sdrtrunk Fsk decoder doesn't use the frequencies for decoding. It correlates the current samples (bit) against a one baud period delayed version and through correlation detects if the current bit/symbol waveform is different from the previous and then xors the output. That way there's no frequency alignment needed. The probable issue is in the sync detect. If the decoded bit stream doesn't match the sync perfectly then it misses the entire message. There are ways to correlate the sync pattern as well to allow for bit errors in the sync but that's not done currently.
ScannerSK
Member
The idea crossed my mind whether reducing the sync pattern from 0101010100001111 down to 00001111 would help however this may introduce more false frames than its worth. It might be fun to try as an experiment to verify what if any difference is noticeable in the number of decoded frames.
Does anyone have an idea as to the best setup to use in order to maximize decoding LoJack transmissions? Would it be an SDR dongle or possibly a discriminator tap and matching interface? Just curious... I have not experimented too much with digital signals other than the 1200 baud National Weather Service/Emergency Alert System S.A.M.E. and now the 1200 baud LoJack systems.
Shawn
ScannerSK
Member
I tried out an SDR dongle and if anything the performance was worse (due to slightly worse reception). I also tried the discriminator tap on my scanner which really crisped up the audio. It appears the output from the discriminator tap improved decoding on one of the three towers however overall the results are inconclusive. I thought I would share just in case anyone was interested.
Shawn
73s
Shawn
73s
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ScannerSK
Member
Tracking/Speed-Up Alert?
Sitting, watching the live LoJack tower data tonight, it occurred to me that it would be nice to have a sound notification each time a new Site ID is received. This would serve as notification that a stolen vehicle in the area covered by the towers has suddenly begun to be tracked by the police. A person could then tune into their scanners to locate and listen to the activity.
For example, my local towers are FA-40, FA-80 and FA-81. When SDRTrunk is initially started, a sound notification would go off for each of these three towers. Following this, a sound notification would only go off when a new Site ID (one not presently shown on the current screen dump) is received signaling that a stolen vehicle has begun to be tracked in the area.
Just something on a wish list.
Currently, what I am doing to watch for new Site IDs (the tracking/speed-up command) is simply to sort ascend the "details" column under the "events" tab and then watching for new Site IDs to appear.
Shawn
73s
Sitting, watching the live LoJack tower data tonight, it occurred to me that it would be nice to have a sound notification each time a new Site ID is received. This would serve as notification that a stolen vehicle in the area covered by the towers has suddenly begun to be tracked by the police. A person could then tune into their scanners to locate and listen to the activity.
For example, my local towers are FA-40, FA-80 and FA-81. When SDRTrunk is initially started, a sound notification would go off for each of these three towers. Following this, a sound notification would only go off when a new Site ID (one not presently shown on the current screen dump) is received signaling that a stolen vehicle has begun to be tracked in the area.
Just something on a wish list.
Currently, what I am doing to watch for new Site IDs (the tracking/speed-up command) is simply to sort ascend the "details" column under the "events" tab and then watching for new Site IDs to appear.
Shawn
73s
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ScannerSK
Member
I verified today the above actually works if you enjoy monitoring LoJack related activity on your scanner or via online feeds. Possibly at some point SDRTrunk will have the capability to sound an audible notification whenever an unusual site ID, actually the speed-up/tracking command, is received.
This morning I noticed an unusual Function 8 site-ID (speed-up/tracking request) begin to appear in the tower data each minute. I turned on the scanner and within minutes located the activity. Police were looking for two white company trucks one of which had LoJack. The vehicles were later recovered unoccupied. Hours earlier before the recovery one of the two vehicles was blowing through stop signs and failing to yield to police. This made for an interesting listen this morning/afternoon.
Viewing Function 8 site-ID/speed-up/tracking commands, there is yet another LoJack being tracked. This one police have yet to recover. They continue to lose the tracking signal or in one instance did not have sufficient backup to continue pursuit. It has been several hours since the police last received a LoJack hit or since the towers last broadcast the Function 8 speed-up/tracking command.
Shawn
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ScannerSK
Member
LoJack Full Circle of Events Captured (Second Example)
I was able to capture a second example of the full circle of events yesterday including the activation in the tower data, a recording of the tracking signal, a recording of the speed-up command from the tower (another Function 8 unusual site-ID) and its effect on the tracking signals, and a recording of the deactivate command from the tower and its effect on the tracking signals.
As far as I can tell, this covers all the basics: activation, reply code, speed-up and deactivation. As for the set rate command I'm not sure it even exists. And whether a transponder transmits a successful activation signal is irrelevant. I have noticed that a transponder upon being successfully deactivated will typically key up for 1-2 seconds with no audio.
Shawn
73s
I was able to capture a second example of the full circle of events yesterday including the activation in the tower data, a recording of the tracking signal, a recording of the speed-up command from the tower (another Function 8 unusual site-ID) and its effect on the tracking signals, and a recording of the deactivate command from the tower and its effect on the tracking signals.
As far as I can tell, this covers all the basics: activation, reply code, speed-up and deactivation. As for the set rate command I'm not sure it even exists. And whether a transponder transmits a successful activation signal is irrelevant. I have noticed that a transponder upon being successfully deactivated will typically key up for 1-2 seconds with no audio.
Shawn
73s
ScannerSK
Member
I discovered today that if I removed some of the lower frequency bass sound out of the scanner's speaker output line then SDRTrunk decodes much better. Possibly the lower frequency bass sound interferes with SDRTrunk decoding. I added a 0.1 uF capacitor in series with the audio line to remove the appropriate amount of bass. This modification along with a slight adjustment of the scanner antenna position allows me at times now to receive all 33 frames from the three local towers.
Shawn
Shawn
- Status
