Location via Repeater Input

dchemist

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#21
Here’s a little proof of concept!
I also had a proof of concept but forgot to download the video and overwrote it. I'm not getting any voice transmission from the local PD but I did get the close call notice when passing one. Wish I wasn't a dumb ass and had video to share.

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InsipidMonkey

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Sounds encouraging! Were you using the CloseCall feature on your Uniden scanner, or were you scanning the repeater input frequencies and got an alert? Do you have it set to record any transmissions on the input frequencies? What was the frequency (and offset from the system in RR)?
 

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#23
Sounds encouraging! Were you using the CloseCall feature on your Uniden scanner, or were you scanning the repeater input frequencies and got an alert? Do you have it set to record any transmissions on the input frequencies? What was the frequency (and offset from the system in RR)?
My alert was from my set of input frequencies, Close Call was disabled at the time. The input frequencies for Washington State Patrol are not listed in the RadioReference database for some reason, I sourced the frequency from here instead: WA State - InterceptRadio.com Wiki

Intercept and RR have differing opinions on the squelch code however, so I have WSP programmed twice; once for the analog CTCSS tones given by Intercept, and again for the digital NAC codes listed in RR. My encounter was on the input frequency of 155.580 listed by IR, but using the NAC code of D50 listed by RR. This was for the Klickitat, Clark, and Skamania county dispatch channel for WSP District 5.
 
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dchemist

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#24
Sounds encouraging! Were you using the CloseCall feature on your Uniden scanner, or were you scanning the repeater input frequencies and got an alert? Do you have it set to record any transmissions on the input frequencies? What was the frequency (and offset from the system in RR)?
My close call was on but it's a different tone/color/flash frequency than what @FoxStang set up for me in the .hpe file. I got the tone 4 fast flashing red light which would indicate input frequency.

I saw the LEO coming opposite direction, no radar. Once he was even with me or just past I got the tone (suggesting he keyed his radio at that time). It certainly wasn't a "save" but it worked .

I did find a setting in the scanner that I think should increase/decrease the close call sensitivity. I'm not sure how it would work if at all. I may play around with it.

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Pho20

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#25
Super interested in this
 

GTO_04

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#26
My close call was on but it's a different tone/color/flash frequency than what @FoxStang set up for me in the .hpe file. I got the tone 4 fast flashing red light which would indicate input frequency.

I saw the LEO coming opposite direction, no radar. Once he was even with me or just past I got the tone (suggesting he keyed his radio at that time). It certainly wasn't a "save" but it worked .

I did find a setting in the scanner that I think should increase/decrease the close call sensitivity. I'm not sure how it would work if at all. I may play around with it.

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No, now that you disclosed that, you MUST play with it so we get more details!:):):)

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dchemist

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#27
No, now that you disclosed that, you MUST play with it so we get more details!:):):)

GTO_04
Here's where I'm at, and here's what I don't understand:

In the BCD436HP, go under "Menu" then "Srch/CloCall Opt" then "Digital Threshold Mode". The three options will be "Auto", "Manual", and "Default". Auto and Default appear to be the same setting (8) but choosing Manual allows you to choose your own threshold. Go back one menu screen and select "Digital Threshold Level". From what I can tell by reading this wiki:
P25 audio decode level adjustment - The RadioReference Wiki

The choices should be 0-20 except on my 436 it says 5 is the lowest. If I understand correctly, setting of 5 would be more selective decoding versus say 20. My thought is, in this application, if you only wanted a proximity notice you could choose a higher value where you many not get the transmission but you would still get the notification. I'm really not sure about this.

On a related note, I did find this older post from Upman that said the BCDx36HP is looking for a 15db gain over ambient to give CC notification. I have no idea how to change that (if it's even possible) but that would explain why some people get feet of CC range while others get miles.
Screenshot_20180811-211030.jpeg


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Edit: I see that he said there is no way to adjust the range.
 

dchemist

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#28
My close call was on but it's a different tone/color/flash frequency than what @FoxStang set up for me in the .hpe file. I got the tone 4 fast flashing red light which would indicate input frequency.

I saw the LEO coming opposite direction, no radar. Once he was even with me or just past I got the tone (suggesting he keyed his radio at that time). It certainly wasn't a "save" but it worked .

I did find a setting in the scanner that I think should increase/decrease the close call sensitivity. I'm not sure how it would work if at all. I may play around with it.

Posted from my Pixel 2 using the RDF Mobile App!
I also need to update this; I have confirmed that my local PD is running encryption: www.broadcastify.com: Benton Police Dispatch Live Audio Feed despite what RR says.

So my one good interaction I've had, according to the instructions @FoxStang provided, was with encryption. The next town over (Bryant, AR) also runs encryption for their PD. I'm going to try to add them in and see if I can get more hits.

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FoxStang

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#29
I also need to update this; I have confirmed that my local PD is running encryption: www.broadcastify.com: Benton Police Dispatch Live Audio Feed despite what RR says.

So my one good interaction I've had, according to the instructions @FoxStang provided, was with encryption. The next town over (Bryant, AR) also runs encryption for their PD. I'm going to try to add them in and see if I can get more hits.

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That makes sense as to why you would have gotten a notification but not heard anything transmitted. I have a local PD programmed in that runs encryption as well.
 

GTO_04

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#30
That is encouraging the CC helps pick up nearby LEOs using encryption! fFortunately there is very little encryption near me. Keep up the good work! Did you set an alert tone for picking up LE talkgroups of does CC provide the ability to set an alert.

I have had very little experience using CC mode since almost everything here is in the clear. This is all VERY helpful information!

GTO_04
 
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dchemist

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#31
That is encouraging the CC helps pick up nearby LEOs using encryption! fFortunately there is very little encryption near me. Keep up the good work! Did you set an alert tone for picking up LE talkgroups of does CC provide the ability to set an alert.

I have had very little experience using CC mode since almost everything here is in the clear. This is all VERY helpful information!

GTO_04
I initially had CC set for tone 4 with fast blue light. Since tone 4 was what @FoxStang choose for input frequency notification, I changed it to tone 7 so I could audibly tell the difference.

I've been playing with CC a lot at work since we're using UHF radios in the field in a relatively remote area. I can routinely (say 70+% of the time) pick up the repeater which is close to a mile from me with dense vegetation in the way.

This whole idea of CC notification based on input frequencies will work. As usual, the devil is in the details.

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GTO_04

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#32
I initially had CC set for tone 4 with fast blue light. Since tone 4 was what @FoxStang choose for input frequency notification, I changed it to tone 7 so I could audibly tell the difference.

I've been playing with CC a lot at work since we're using UHF radios in the field in a relatively remote area. I can routinely (say 70+% of the time) pick up the repeater which is close to a mile from me with dense vegetation in the way.

This whole idea of CC notification based on input frequencies will work. As usual, the devil is in the details.

Posted from my Pixel 2 using the RDF Mobile App!
I know it's early on in your research, but at this point do you think it would be better or worse just to program the input frequencies of a given agency and scan them conventionally, using audio alerts to indicate a nearby mobile LEO transmitter? I am trying that but am not picking up anything. But my local agencies RARELY use encrtyped TGs so far. It is mostly the tac channels. We had a school shooting back in May, and the encrypted TGs were very active, but I did not have the input frequencies programmed back then and ready to scan.

GTO_04
 

dchemist

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#33
I know it's early on in your research, but at this point do you think it would be better or worse just to program the input frequencies of a given agency and scan them conventionally, using audio alerts to indicate a nearby mobile LEO transmitter? I am trying that but am not picking up anything. But my local agencies RARELY use encrtyped TGs so far. It is mostly the tac channels. We had a school shooting back in May, and the encrypted TGs were very active, but I did not have the input frequencies programmed back then and ready to scan.

GTO_04
At this point in time, I would recommend doing both (at least that's what I'm doing). The reason I'm suggesting this is that we are uncertain what the offset for the input frequencies are on a P25 system. There is evidence to suggest most are 45 MHz lower than the repeater but there are no hard and fast rules. By setting CC on for band 8, you will get the exact frequency during the alert. This will allow you to double check against what you may have programmed for the input frequencies. With CC off only using the suspected input frequencies you have no way to confirm if you are correct or not.
 

FoxStang

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#34
I know it's early on in your research, but at this point do you think it would be better or worse just to program the input frequencies of a given agency and scan them conventionally, using audio alerts to indicate a nearby mobile LEO transmitter? I am trying that but am not picking up anything. But my local agencies RARELY use encrtyped TGs so far. It is mostly the tac channels. We had a school shooting back in May, and the encrypted TGs were very active, but I did not have the input frequencies programmed back then and ready to scan.

GTO_04
For me so far, manually programming only the frequencies I want is the way to go. Even after configuring Close Call to run on only the VHF/UHF bands and setting it to ignore broadcast signals, it still picks up tons of stuff I don't care about like business radios, transit comms, and FRS/GMRS toy radios.

At this point in time, I would recommend doing both (at least that's what I'm doing). The reason I'm suggesting this is that we are uncertain what the offset for the input frequencies are on a P25 system. There is evidence to suggest most are 45 MHz lower than the repeater but there are no hard and fast rules. By setting CC on for band 8, you will get the exact frequency during the alert. This will allow you to double check against what you may have programmed for the input frequencies. With CC off only using the suspected input frequencies you have no way to confirm if you are correct or not.
I'll play around with CC some more for that purpose. I'm heading to Ham Radio Outlet on Thursday, I'm thinking I may bite the bullet and pick up an SDR receiver and base station antenna to use in a spectrum analysis role to properly identify the P25 input offsets near me. If they really aren't on the standard -45MHz offsets, then we could share the SDR between members since each area would be unique and need local frequency identification. The waterfall display seen in the last half of this video would make that a very simple task, requiring only a couple minutes of reception for each site in the network.
 

InsipidMonkey

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#35
I'm thinking I may bite the bullet and pick up an SDR receiver and base station antenna to use in a spectrum analysis role to properly identify the P25 input offsets near me.
You can pick up SDR dongles from eBay or Amazon for $20 or less, and most include a cheap antenna. They're actually surprisingly capable, and it's cool to see the waterfall plot as you scan through different frequencies. There are a number of decoding programs available as well for things like DMR, NXDN, ProVoice, P25 Phase 1 & 2, and even things like weather station data, ADS-B data, AIS ship data, pager messages, etc. Well worth the small investment if you have any interest in radio.
rtl-sdr.com - RTL-SDR (RTL2832U) and software defined radio news and projects. Also featuring Airspy, HackRF, FCD, SDRplay and more. is a wealth of information on the subject.
 

dchemist

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#36
For me so far, manually programming only the frequencies I want is the way to go. Even after configuring Close Call to run on only the VHF/UHF bands and setting it to ignore broadcast signals, it still picks up tons of stuff I don't care about like business radios, transit comms, and FRS/GMRS toy radios.



I'll play around with CC some more for that purpose. I'm heading to Ham Radio Outlet on Thursday, I'm thinking I may bite the bullet and pick up an SDR receiver and base station antenna to use in a spectrum analysis role to properly identify the P25 input offsets near me. If they really aren't on the standard -45MHz offsets, then we could share the SDR between members since each area would be unique and need local frequency identification. The waterfall display seen in the last half of this video would make that a very simple task, requiring only a couple minutes of reception for each site in the network.
I agree with @FoxStang reasoning. The way he is set up, he'll get a notification whenever he's within range of the notification without having to overcome the 15 db gain required for CC. I'm not getting many hits within my town of 30k which probably isn't 5-7 miles across so I'm suspecting that I may not have the correct input frequencies programmed. This wouldn't surprise me as I/we used RR to source the information and it also doesn't list my local PD as using encryption. I too feel like it may be time to go camp at the station for a few and see what I can pick up.

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dchemist

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#37
You can pick up SDR dongles from eBay or Amazon for $20 or less, and most include a cheap antenna. They're actually surprisingly capable, and it's cool to see the waterfall plot as you scan through different frequencies. There are a number of decoding programs available as well for things like DMR, NXDN, ProVoice, P25 Phase 1 & 2, and even things like weather station data, ADS-B data, AIS ship data, pager messages, etc. Well worth the small investment if you have any interest in radio.
rtl-sdr.com - RTL-SDR (RTL2832U) and software defined radio news and projects. Also featuring Airspy, HackRF, FCD, SDRplay and more. is a wealth of information on the subject.
If you decide to go that route (Looks like I am), this guy is the Bob Ross of SDR. I could listen and watch for days. He does a really nice five part series to get started.

#1
#2
#3
#4
#5

He does go a bit further than just a spectrum analyzer but there is some fantastic detailed analysis for us visual and auditory learners.

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FoxStang

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#38
@InsipidMonkey
Thanks for the info! I am a ham operator so I'm sure I'll come up with all kinds of uses for an SDR receiver after using it for what we're trying to do. I was at my local Ham Radio Outlet previously and mistakenly thought the least expensive SDR was the SDRPlay unit that they had for $120. I went ahead and ordered a NooElectronics dongle on Amazon last night along with a new laptop battery. I'll get that all set up, plug in the lead for my car's scanner antenna, and probably spend a day camping outside police stations and radio tower sites.

Nice vids @dchemist , SDR# was the program I had my eye on for this purpose.
 

dchemist

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@InsipidMonkey
Thanks for the info! I am a ham operator so I'm sure I'll come up with all kinds of uses for an SDR receiver after using it for what we're trying to do. I was at my local Ham Radio Outlet previously and mistakenly thought the least expensive SDR was the SDRPlay unit that they had for $120. I went ahead and ordered a NooElectronics dongle on Amazon last night along with a new laptop battery. I'll get that all set up, plug in the lead for my car's scanner antenna, and probably spend a day camping outside police stations and radio tower sites.

Nice vids @dchemist , SDR# was the program I had my eye on for this purpose.
Well sometimes I really hate you guys for the rabbit holes you send me down. I just spent the last hour and a half having my eyes opened to the capabilities of SDR!


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Edit: towards the end is a nice little section on pinpointing direction. It's incredibly complicated but sounds like really smart people are figuring it out.
 

FoxStang

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Well sometimes I really hate you guys for the rabbit holes you send me down. I just spent the last hour and a half having my eyes opened to the capabilities of SDR!


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Edit: towards the end is a nice little section on pinpointing direction. It's incredibly complicated but sounds like really smart people are figuring it out.
You're telling me. I knew somewhere in the back of my mind that SDR could be used to sniff ADS-B transponders, but that got brought back up to the forefront right about the same time I was coming across an old video of aircraft enforcement relatively near to me. For a while I had wanted to get a PCAS MRX as an aircraft countermeasure, but now using the $20 SDR receiver I already bought sounds a little more appealing.