Comtronics MotoTrbo TRS Decoding Project

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garys
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Comtronics MotoTrbo TRS Decoding Project

#1 Post by garys » 16 Mar 2016 20:58

This is a much smaller network, with far fewer users. Transmit power also seems to be lower than the larger ICE system.

I've been working on decoding the system for the past several days. One of the handicaps is that Airspy is a much better receiver than any of the R820T2 dongles. I get lots of control channel data, but the voice channels are often down in the mud.

Anyway, I have the OTA channel order for Sites 2 and 3 figured out. I can't find Channel 9/10 for Site 2. I attribute that to the variation in transmit power that I've noticed in both networks.

For Site 1, I have the following

Freq Use OTA
938.3875 Voice & CC 1
936.7500 Voice 3
939.4625 Voice 5
938.6500 Voice 7
935.4625 Voice 9

I'm 99% sure that this is correct, but the power fluctuations make me a bit unsure.

If someone with a SDR set up and DSDPlus can confirm this, I'll update the Wiki.

Thanks.
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#2 Post by bfrederi » 26 Apr 2016 20:43

Hi garys,

I started exploring this system this weekend, trying to initially nail things down on my own, and then comparing my results against your posts, and the FCC DB listings for WPHN648.

Do you know why the sig strength for the voice channels for 139-1 (Boston) vary so wildly? I would expect them all to be about the same as the CC, but for 139-1, the only voice channel that is completely readable at my QTH is 936.75. (Also, this appears to be chs 7 & 8 rather than 3 & 4.) The other three voice channels are barely above the noise level here. Much weaker than the CC.)

139-4 (Peabody) channels are all very strong -- all as strong as the CC, as I would expect. Does site 139-1 actually use voice channels from different sites? Or are they on directional antennas pointing in different directions?

Interesting system, and much easier to get your arms around than ICE system 134. But seems to have its quirks.
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#3 Post by garys » 26 Apr 2016 22:43

I've noticed varying signal strength, and not just on the Comtronics system. I see it with some of the ICE channels as well. I think it's just radio to radio variation. It wouldn't make sense to have transmitters at different sites, but I suppose it could happen.

I was up in Burlington last week and worked on figuring out the Peabody system. I had limited time so I worked on figuring out the OTA channel order more than the talk groups. Next time I'm up there and have some spare time.

You might be right about Boston. I hope to get to a good spot to monitor Boston and confirm the OTA order. After that, I want to spend some time identifying talk groups and users. I can't receive it all too well from my home, so I have to go mobile to hear that site.

I was out in western MA yesterday and was able to confirm the control channel for Paxton. Over about 30 minutes of listening, there was no voice activity and no indication of other channels being used. I think the system in general is still in build out phase, so there will be plenty of changes for people to track.

I also got to Holyoke and confirmed the control channel and the other two frequencies, but was not able to confirm the OTA. Channel order. Channel 1 as listed in the Wiki appears to be correct, but it's possible that 3/4 and 5/6 are backwards. It's not a very busy system, so over 20 minutes of listening I was only able to hear a couple of talk groups. I'll work on that next time I'm out that way. Whenever that may be.

Overall, the Comtronics system is much smaller. There is also one UHF and one VHF MotoTrbo system being built. I don't know how fast that is going as all I get is the network ID and a control channel. No activity other than that.

One other thing I've noticed is that the control channel doesn't seem to rotate as the ICE sites do. Which makes things a bit easier in some regards.

I'd still like to confirm the ICE Medford (Site 4) frequencies and channel order. If you're interested in working on that, PM me and I'll send you some information.
bfrederi wrote:Hi garys,

I started exploring this system this weekend, trying to initially nail things down on my own, and then comparing my results against your posts, and the FCC DB listings for WPHN648.

Do you know why the sig strength for the voice channels for 139-1 (Boston) vary so wildly? I would expect them all to be about the same as the CC, but for 139-1, the only voice channel that is completely readable at my QTH is 936.75. (Also, this appears to be chs 7 & 8 rather than 3 & 4.) The other three voice channels are barely above the noise level here. Much weaker than the CC.)

139-4 (Peabody) channels are all very strong -- all as strong as the CC, as I would expect. Does site 139-1 actually use voice channels from different sites? Or are they on directional antennas pointing in different directions?

Interesting system, and much easier to get your arms around than ICE system 134. But seems to have its quirks.
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#4 Post by N1ZZN » 20 Jun 2016 14:02

N1ZZN wrote:I'm currently right under the ICE site in Plymouth (pine hills) and there's a site here. CC is 935.950 Color Code 0. Another freq is 935.175. Not sure how to figure out LCNs, etc., but it's another one to look out for.
Well I'm back in Marshfield, trying 935.950 in the Analyze mode on the 536. Looks like the System ID is 8B, which is 139 decimal, site ID 6, so this may be a Comtronics system, not ICE. It's definitely not in Marshfield, but maybe on another tower on the pine hills in Plymouth, or might they be leasing space from ICE? Will take more research to confirm...
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#5 Post by garys » 20 Jun 2016 15:05

935.950 is listed in the Comtronics Wiki page as the Control for Site 6. The Wiki says Marshfield, but that might be an educated guess. Finding a second frequency for that is helpful. Good work!
Figuring out LCNs with DSD+ can be time consuming.
The way that I've found works best, and others might have a more efficient way, requires two SDR set ups. First, I use FMP24 and DSD-CC set up on the control channel. I watch for activity on the control channel and use SDR# and DSDPlus to sweep through the 935-939 band looking for activity. DSD plus will show the network, site, and OTA channel of the voice channel. It takes some luck and time to catch the voice channels, but it can be done. It works better if you are in close proximity to the transmitter site as you can set up your antenna to only receive near by frequencies. That reduces the number of potential frequencies that you have to look at.

When I finally figured out what was going on with the Comtronics Needham site, I drove over to You Do It and used a really cheap antenna. The transmitter site is almost directly across the road from YDI, so I was able to find the active frequencies and the LCN and OTA numbering pretty quickly.

I used a similar technique to find the two new channels on ICE Site 15, but it took a lot longer because I'm nowhere near Marshfield and had to search through the entire band about 100 times before I happened upon the two frequencies.

This site, http://wireless2.fcc.gov/UlsApp/UlsSear ... ey=1929089, shows a lot of information for Network 139, including sites. The Marshfield site is listed as 117 Grove Street, Marshfield. Which is the transmitter site for WATD.

Frequencies listed for Site 6 are,
935.95000000
938.38750000
939.41250000

As we know, sometimes the actual frequencies differ from what the FCC data shows.
N1ZZN wrote:Well I'm back in Marshfield, trying 935.950 in the Analyze mode on the 536. Looks like the System ID is 8B, which is 139 decimal, site ID 6, so this may be a Comtronics system, not ICE. It's definitely not in Marshfield, but maybe on another tower on the pine hills in Plymouth, or might they be leasing space from ICE? Will take more research to confirm...
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#6 Post by garys » 21 Jun 2016 23:08

Well, this was a surprise. While trying to chase down ICE Site 34, I was sitting north of Boston and plugged in 939.1875. I got control channel data, only it for Comtronics Site 7, Framingham. Which makes me think that Site 34 is south of Boston or maybe even in Rhode Island. I'll look into that next week when I'm down that way.

Tonight, I plugged in 936.2000, which is today's ICE Sudbury control channel. I received a good signal, but it's for Comtronics Site 8, Mashpee. That is weird, since I never receive anything that far away.

I blame the full moon, but I'm going to plug in some other control channels and see if I can track down some of the elusive ICE sites.
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#7 Post by garys » 07 Jul 2016 16:30

I got to Marshfield today and was able to confirm some information for Site 6. It appears to be a pretty low powered site as I set up about 1 air mile from the licensed site at WATD (170 Grove Street). I had anticipated using a rubber ducky attached directly to my mobile SDR set up, but got no signal and ended up putting the Larsen triband antenna on a mag mount on the roof of the truck. ICE Site 15 came pounding in, but the Comtonics signal was much weaker. I updated the Wiki with my findings. I was not able to track down the two additional frequencies as I ran out of time. If I can get over there again in the next couple of weeks I'll see what I can do.
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#8 Post by N1ZZN » 08 Jul 2016 09:33

garys wrote:I got to Marshfield today and was able to confirm some information for Site 6. It appears to be a pretty low powered site as I set up about 1 air mile from the licensed site at WATD (170 Grove Street). I had anticipated using a rubber ducky attached directly to my mobile SDR set up, but got no signal and ended up putting the Larsen triband antenna on a mag mount on the roof of the truck. ICE Site 15 came pounding in, but the Comtonics signal was much weaker. I updated the Wiki with my findings. I was not able to track down the two additional frequencies as I ran out of time. If I can get over there again in the next couple of weeks I'll see what I can do.
I still disagree that Site 6 is located in Marshfield. I'm line of site from the WATD site, and can barely hear it. I'm quite certain it's located somewhere on the pine hills in Plymouth.
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#9 Post by garys » 08 Jul 2016 09:55

You may well be right. I was going by the FCC licensing data, but the signal was very weak in Marshfield. I was in the mall where Ocean State Job Lot is located and got very weak signal. I headed back west Route 139 and the signal got weaker fairly quickly. If I can get down to Plymouth in the next couple of weeks or so, I'll try from there.
N1ZZN wrote:I still disagree that Site 6 is located in Marshfield. I'm line of site from the WATD site, and can barely hear it. I'm quite certain it's located somewhere on the pine hills in Plymouth.
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#10 Post by N1ZZN » 20 Jul 2016 13:16

Just confirmed that Network 139, Site 6 Comtronics is on the tower just south of ICE's on the pine hills in Plymouth. 379 State Road. Under ICE's tower, I could hear it with no antenna, but not great. Under the 379 State Rd tower, it's full scale with no antenna.
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#11 Post by Mark SNE Moderator » 20 Jul 2016 14:18

The ICE tower is behind Serious Cycles, at top of the Pinehills, IIRC, which is 265 State Rd. There is a smaller tower just past it, would that be the one you are referring to, Jeff?


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#12 Post by garys » 20 Jul 2016 14:47

Good find. Depending on what my work schedule is, I might get down that way tomorrow and see if I can hunt down the two missing frequencies.
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#13 Post by garys » 20 Jul 2016 15:06

Google Maps shows that as 465 State Road. It's a small tower, but a number of the Comtronics sites seem to be on smaller towers.
Mark SNE Moderator wrote:The ICE tower is behind Serious Cycles, at top of the Pinehills, IIRC, which is 265 State Rd. There is a smaller tower just past it, would that be the one you are referring to, Jeff?


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#14 Post by N1ZZN » 20 Jul 2016 16:13

Yes, sorry I was going by a sign on the building for the address, must be labeled wrong or something... The tower is technically just east of the ICE tower/serious cycles, boat yard, etc., south as you continue down route 3A
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#15 Post by W1KNE » 20 Jul 2016 20:01

That tower is owned by Entergy Nuclear. I believe it is used for their outdoor notification system, as next to the tower is one of the outdoor loudspeakers.
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#16 Post by Mark SNE Moderator » 20 Jul 2016 20:32

Nitpicking, but Serious Cycles is 265 State Rd.
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#17 Post by garys » 20 Jul 2016 21:26

That's where the ICE tower is, but the other tower is at 465. Not much difference as they are pretty close.
Mark SNE Moderator wrote:Nitpicking, but Serious Cycles is 265 State Rd.
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#18 Post by garys » 21 Jul 2016 15:19

I got to Plymouth today and was able to track down the two missing frequencies. One odd thing on 935.175 that threw me for a while is that there signal on the frequency not related to the trunk. A strong digital signal that was not DMR would come on the air for about five seconds at a time. Those transmissions did not correlate to trunk activity at all. Then when channels 5 of 6 were selected by the trunk, I received DMR audio on the frequency.

There was no 900 Mhz traffic coming from the larger tower, but there was a strong digital signal on UHF T that overrode some of the public safety traffic on my 536HP. Maybe there is a UHF DMR trunk site.

The wiki is updated with the new information and a change of location from Marshfield to Plymouth.
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#19 Post by Mark SNE Moderator » 21 Jul 2016 15:39

So there is no longer 900MHz traffic from the ICE tower? Are the frequencies we currently have for it outdated?
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#20 Post by garys » 21 Jul 2016 17:04

If that was the analog site, I would say that is correct. The Kingston ICE site is off of Route 44 at Route 80. At least it looks like all of the other big ICE sites (Quincy, Foxboro, West Bridgewater) I'm familiar with. That site is very active with 900 MotoTrbo activity. The tower behind the cycle/boat shop on State Road doesn't appear to be doing anything on 900.
Mark SNE Moderator wrote:So there is no longer 900MHz traffic from the ICE tower? Are the frequencies we currently have for it outdated?
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#21 Post by Mark SNE Moderator » 21 Jul 2016 17:29

Interesting, thanks for the update.
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#22 Post by garys » 21 Jul 2016 18:05

I should add that last time out, I parked in the Walmart parking lot at the mall off of Route 44. The frequencies listed for Kingston hammered the dongles and I had to turn down the gain. Which is pretty much what happened on the Comtronics site today.


Mark SNE Moderator wrote:Interesting, thanks for the update.
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#23 Post by N1ZZN » 25 Jul 2016 10:44

Seems that Site 11 may be on Copicut Hill in Fall River. I haven't heard any other frequencies besides 939.925, but will keep an eye on it during future visits to the area.
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#24 Post by Scott » 21 Aug 2016 13:22

Talkgroup 125 on Network 139 is definitely "maritime" in nature from past transmissions heard. Today I confirmed the MV Brant Point operating on this TG. Brant Point was formerly a HyLine vessel but appears to be homeported in Boston now. I'm not sure what company owns the vessel but if someone does that would serve to identify this talkgroup, which has become very active as of late. I've been to a few maritime based websites but one indicates that I must be a "premium user" in order to see who owns the ship.

I'm sure a few of you may have the answer to this question.
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#25 Post by garys » 21 Aug 2016 14:06

That matches what I've heard. I think I'm the one that listed it as a "whale watch cruise" in the Wiki, with an unknown home port.
Scott SNE Webmaster wrote:Talkgroup 125 on Network 139 is definitely "maritime" in nature from past transmissions heard. Today I confirmed the MV Brant Point operating on this TG. Brant Point was formerly a HyLine vessel but appears to be homeported in Boston now. I'm not sure what company owns the vessel but if someone does that would serve to identify this talkgroup, which has become very active as of late. I've been to a few maritime based websites but one indicates that I must be a "premium user" in order to see who owns the ship.

I'm sure a few of you may have the answer to this question.
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