Location via Repeater Input

Discussion in 'CB & Scanner Discussion' started by FoxStang, Aug 4, 2018.

  1. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    Piggybacking off this thread by @RadarSammich and what I posted there: https://www.rdforum.org/index.php?threads/77511/

    The idea here is to try to emulate the function of the Target BluEye system by programming a scanner to monitor the radio input frequencies of a given agency, and sound an alert when one is picked up to differentiate from regular repeater output traffic. This will never be as effective since it relies on an active transmission versus the passive emissions present in the TETRA radio system that the BluEye relies on, but will at least indicate when an LEO is near enough to you to be within the typical radio horizon (5-7 miles or so) and could possibly indicate a more precise location depending on what they are saying during the transmission. Under perfect circumstances on the highway, you could be alerted to the presence of an LEO several miles before you were close enough to detect their radar unit. Unlike BluEye, with this method you can also narrow your scope to only LE radios rather than all emergency vehicles.

    I have been running a list of State Police frequecies on my own Uniden BCD436HP scanner over the last few days, and have successfully received a couple of transmissions from nearby LEOs however none have been in my immediate path of travel; either adjacent highways or surface streets. So far I am limited to conventional systems but I am also experimenting with trying to identify the input for my local P25 trunked systems based on the standard offsets for their control frequencies and the known talkgroup IDs listed on RadioReference. Once I can get that part figured out, I want to expand my monitor list to include the local sheriffs who only operate on the regional P25 system as well as the traffic units of the largest local PDs.

    The problem I have is that I am a sample size of 1 for testing. I have limited driving time, and even more limited encounters with the state police as I'm typically driving in metropolitan areas. I would like to invite anyone else in the Northwest area to download my current favorites list below (.hpe file format, created in Sentinel for Uniden BCDx36HP) and run it to report back on your success rate in capturing transmissions. Bonus if you can match it to the LEO on the highway, and capture it on camera. The file currently only includes the conventional system input frequencies, the simplex frequencies (car-to-car channels) for the Oregon State Police in the northwest region of the state, and districts 1, 2 and 5 of the Washington State Patrol. I will update if/when I am able to locate the correct frequencies for the P25 systems and expand to other areas of those two states.

    If there is enough interest in this endeavor, I may start creating files for other states or regions as well. I know there is a large chunk of membership on this forum in the Houston area of Texas for example, and the TXDPS system looks like it may be documented well enough on RadioReference to make it relatively easy to program. I am just one person doing this in my spare time though, so no promises on how long that may take. Let me know if that's something you are interested in for your area, and I'll look into how quickly I can put it together or if it is even possible with different systems or encryption being used.

    The Sentinel favorites list linked below is currently set up to use the #4 alert tone and fast-blinking red indicator light for any of the frequencies listed. It will only work if you have a BCD436HP or BCD536HP scanner.

    In software terms, this is pre-Alpha. Nothing promised in terms of functionality or performance. I greatly appreciate anyone who takes the time to help me refine this!

    Dropbox - LEO Input Freqs.hpe
     
    Last edited: Aug 4, 2018
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  2. dchemist

    dchemist Premium Member Advanced User Premium Member

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    If you'd be willing to write up a brief list of instructions, I'd get the ball rolling on Arkansas.

    Posted from my Pixel 2 using the RDF Mobile App!
     
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  3. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    1) Go to the State Police page on RadioReference and use the drop-down menu to select "Input Frequencies - Shown"

    2) Open Sentinel and create a favorites list named whatever you like, then right-click on it and select "Program Favorites List"
    Program.jpg

    3) As applicable, create a system, department, and list of channels in Sentinel using the input frequencies from the RadioReference database. If they are not listed, you may have to do some in-depth searching to locate the correct ones. I had to find an alternate resource for some of the Washington State Patrol channels. Be sure you have the correct CTCSS, DCS, or other squelch code for the channel in the "Audio Option" column.
    List.jpg

    4) Set an alert tone and light option using the two columns to the right (you can copy/paste ranges of cells like a spreadsheet in Sentinel, making this easy)
    Alerts.jpg

    5) Upload to the scanner over USB connection and make sure the list is enabled for monitoring and you're done!

    It looks like nearly all of Arkansas State Police other than their Commercial Truck Enforcement channel is on a P25 Phase 1 system, making this a much more difficult prospect for your state. Programming a P25 system is more complex since you'll have multiple networked repeater sites with mountains of different frequencies to enter. I still haven't properly figured out how to identify the input frequencies for P25 systems even with a couple hours of dredging different radio forums.
     
    Last edited: Aug 4, 2018
  4. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    My current theory and method of trying to identify P25 inputs is as follows:

    Most radio bands used by repeaters have a "standard offset" used to identify their input frequency, that is, a typical difference in frequency between their input and output. For the 800MHz band, the standard offset is -45MHz so it follows that a repeater channel of 850MHz should have a corresponding input of 805MHz. Offset - The RadioReference Wiki

    Using this random repeater site I picked as an example, you can see two "locations" listed. 1 being the tower itself (class code FB2 for repeater), and 2 being the associated mobile units (handhelds/vehicle systems, class code MO for mobile station)
    base mobile.png

    You can see that the mobiles are licensed for frequencies that correspond to the repeater, but 45MHz below, indicating that these should be the input frequencies for that particular repeater's channel pairs as they follow the standard 800MHz offset.
    pair.png
    The Emission designator 16K0F3E meaning analog FM mode, and 16K0F9W meaning digital operation.

    So, my idea so far has been that programming the P25 system to the scanner by using what should be the input frequencies for each site based on the standard offset but otherwise retaining the same talkgroup IDs (TGID) for each department/channel should allow the same operation as what I described in the first post with a conventional system.

    I have been paying attention to the hits I have gotten so far and haven't had one come across using my experimental P25 inputs, but I don't have many of them entered yet and it has only been a few days. If anyone has more knowledge to offer as far as P25 system operation, I'm glad to hear it. I learn fast but I *am* still learning and pretty new to the whole deal.
     
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  5. dchemist

    dchemist Premium Member Advanced User Premium Member

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    Awesome, write up! I'll see what I can do with it and report back, thanks!!!

    Posted from my Pixel 2 using the RDF Mobile App!
     
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  6. dyn0mitemat

    dyn0mitemat Premium Member Advanced User Premium Member

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    You guys are awesome, keep that up and i may pick up a scanner again
     
    Last edited: Aug 5, 2018
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  7. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    Here’s a little proof of concept!
     
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  8. dchemist

    dchemist Premium Member Advanced User Premium Member

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    So starting with my local public service (Benton, AR), there are two FCC licences issues for 155 MHz. Additionally they are on the statewide AWIN system. The problem I'm seeing so far is how to differentiate LE from other public service in the AWIN (P25 Phase 1) system. Am I missing something obvious? Screenshot_20180804-181312.jpeg Screenshot_20180804-181110.jpeg Screenshot_20180804-180951.jpeg Screenshot_20180804-222613.jpeg Screenshot_20180804-175550.jpeg

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  9. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    @dchemist You are missing something, but it isn't simple at all. You've got the same thing going on as I do in my area, where some agencies are using a mix of conventional and trunked radio systems.

    What you're seeing on the main page there at www.radioreference.com: Saline County, Arkansas (AR) Scanner Frequencies and Radio Frequency Reference is all the conventional system channels, where each frequency has only one user or purpose. You can select the box to show the input frequencies on this page and simply add those to your list in Sentinel.
    Screen Shot 2018-08-04 at 11.03.33 PM.png

    Looks like Benton has just two frequencies on this conventional system for their police, which is nice and simple. 158.895 would be the input for dispatch (with DCS code 503), and 159.150 is the input for their secondary tactical or "tac" channel (with a CTCSS tone of 127.3)
    Screen Shot 2018-08-04 at 11.04.05 PM.png
    system.png
    audio option.png

    Now here is where things get confusing, difficult, and extremely tedious in a hurry. The remainder of Benton Police Department's channels are on the AWIN system, which is a trunked P25 network. That humongous table of frequencies with some highlighted in red and blue that you posted is the list of every single frequency in the entire statewide system. This is the part I mentioned I am still trying to finesse myself.

    First, the bad news. Trunking systems mean that it is possible for ANY of the frequencies on that whole table to be used by ANY entity listed further below past the heading "System Talkgroups". In Sentinel, you will have to create a new system for AWIN as "P25 Trunked", add Sites under the correct tab, and add the offset of each red and blue frequency to a site. That is the tedious part, but if you click on the name of any repeater site on RadioReference it will give you a circle on a map representing that repeater's approximate range. For our purposes, you only need to add the offset frequencies for any site that has coverage over the area you want to have alerts for.
    Screen Shot 2018-08-04 at 11.26.54 PM.png
    Since we only need the control channels, the correct input frequencies for this repeater should be 807.3375 and 807.4875 according to the standard offset, corresponding to the primary and alternate control frequencies in the picture above.
    sites.png
    site 1.png

    Now the good news. Trunked systems make use of what are called Talkgroups, an identifier that tells the trunking controller which group the transmitter is associated with and which radios need to receive the message. Go back to the AWIN page on RadioReference and scroll down to the "System Talkgroups" heading I mentioned, just below the site frequency table. This lists all the different groups that have access to AWIN. Now that the tedium of entering all the possible input frequencies is done, you can simply switch back to the "Departments" tab in Sentinel and create one for Benton PD. Add in channel rows for Benton (just three here, Dispatch, Tac 1, and Tac 2) and then under the "TGID" column, enter the value from the "DEC" column in RadioReference (this is the Talkgroup ID "TGID" expressed in decimal form). Set the alert tone/light you want just like with conventional systems, and you're done!
    Screen Shot 2018-08-04 at 11.33.49 PM.png
    tgid.png

    Now, assuming you have entered all the site frequencies for all of AWIN, adding monitoring capability for any other agency covered by this network is as simple as creating a new "Department" for them and entering their TGIDs. In this particular case, that opens up an incredible range of access covering all of the state police in addition to a majority of county agencies.

    BUT -- And this is a big "BUT" -- PLEASE remember that everything I just said about this method for P25 systems is still experimental! I still have not been able to confirm that this method is effective for the purpose of this whole exercise.

    EDIT: Added Sentinel screenshots
     
    Last edited: Aug 5, 2018
  10. dchemist

    dchemist Premium Member Advanced User Premium Member

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    Excellent! So I'm still a bit asleep but let me grab my coffee and decipher this. Thanks!!! I'll be sending you a PM in a bit to share something I was told last night.

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  11. fireparamed

    fireparamed Learning to Fly Beginner User

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    8EBFA46E-39A5-44F9-8A55-9650A1CBB78F.png This same question was asked on radio reference about tracking inputs using a scanner. UPman is basically the Uniden expert and answered the question. I’ve posted the screenshot of his answer for you.

    Good luck!
     
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  12. InsipidMonkey

    InsipidMonkey Premium Monkey Advanced User Acceptus Premium Member

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    I wonder if it would be possible to scan the input frequencies individually as P25 simplex systems and filter by TGID or radio ID?
     
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  13. dchemist

    dchemist Premium Member Advanced User Premium Member

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    Ok, so the conventional set up was pretty straight forward, once I followed your directions. Quick question: what, if any, did you set your range to under the location tab?
     
  14. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    I'll try that next if I'm still not receiving any P25 hits as-is. That will be a serious time investment

    I didn't bother with that just yet, my scanner takes 10x the amount of time going through all my normal channels as the input frequency list, so I haven't felt the need to enter locations for everything.
     
  15. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    Interesting, hopefully it doesn't try to automatically "correct" all of my manually-entered offsets since I didn't alter the band plan
     
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  16. dchemist

    dchemist Premium Member Advanced User Premium Member

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    Oh, that would suck so bad!

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  17. dchemist

    dchemist Premium Member Advanced User Premium Member

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    So I want to give an update. It took me all damn day and several PMs to @FoxStang but I'm up and running for the local PD. It's quiet so far but I'm going to leave this running until I go to bed. Additionally, there is a possibility that the offset on P25 trunked system isn't always 45 MHz. I haven't found any evidence of what other possibilities there are so I'll have to stick to 45 MHz for now. I plan on adding the neighboring PD and county as the week goes so we'll see what happens.

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  18. dchemist

    dchemist Premium Member Advanced User Premium Member

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    So I had a chance to visit with the radio guy at work today and turns out he was on the committee that implemented the AWIN system (Arkansas's Statewide Digital Trunking System). He's giving me some 800 MHz stuff (mainly antenna, trunk mount, etc) later this week. I'll see if I can work out an answer about close call and offset frequencies. I feel like if anyone in this state would know it would be him.

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  19. FoxStang

    FoxStang Sly fox, dumb bunny. Advanced User Premium Member

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    Awesome, nothing like getting it straight from the source!
     
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  20. dchemist

    dchemist Premium Member Advanced User Premium Member

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    So I spoke with "The Radio Guy" again today. He said that 45 MHz is the norm not the standard. He said it's probably left over from the conventional systems but even those will only be 45 MHz offset whenever they don't interfere with anything else.

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