Troop B signal

[fog]

I've found that I'm missing a decent amount of transmissions from Troop B on 154.935. Sometimes the radio (Pro96) just won't output any audio at all, other times it switches to FM and digital noise comes through... This noise sometimes sounds "different," making me wonder if there's intermittent crypto being used?

Or are they still running simplex? That would explain why I sometimes only heard one side of a conversation.

Just wondering if anyone else is having trouble monitoring them?

 

[ecps92]

There was a previous thread [1-2 yrs ago] about the NHSP also running Data on the Audio channels.

I've found that I'm missing a decent amount of transmissions from Troop B on 154.935. Sometimes the radio (Pro96) just won't output any audio at all, other times it switches to FM and digital noise comes through... This noise sometimes sounds "different," making me wonder if there's intermittent crypto being used?

Or are they still running simplex? That would explain why I sometimes only heard one side of a conversation.

Just wondering if anyone else is having trouble monitoring them?

 

[PeterGV]

Bill is correct: The "Car 54 Project" (fancy Police communications system developed by the University of New Hampshire and used by NHSP) uses intermixed data and voice on the same channel. If you're seeing your radio pause on the channel, but output no audio... this is almost certainly what's going on.

Note that there's also "direct" use of the channel for local communications (such as when you see 2 officers on construction duty). It's possible in this case to only hear the closer of the two units.

Finally, I *did* at one time have a radio (an XTS-3000) that would (seemingly randomly) miss certain P25 transmissions... despite quite a lot of effort I could never find out why. I got rid of the radio, never saw it happen again (with any other radio or scanner).

Peter
K1PGV

 

[fog]

Bill is correct: The "Car 54 Project" (fancy Police communications system developed by the University of New Hampshire and used by NHSP) uses intermixed data and voice on the same channel.

Out of curiosity more than anything, what's the data? Is it AVL or MDT, or something else?

Note that there's also "direct" use of the channel for local communications (such as when you see 2 officers on construction duty). It's possible in this case to only hear the closer of the two units.

Finally, I *did* at one time have a radio (an XTS-3000) that would (seemingly randomly) miss certain P25 transmissions... despite quite a lot of effort I could never find out why.

See, I had that happen a few times back when I had a VHF ASTRO Saber, but it still happens every now and then with a Pro-96. That's what led me to wonder if it was someone using encryption, and getting replies in the clear. But I think it's just as likely that I just have a weak enough signal that reception on an HT is so-so at best.

 

[n1das]

Finally, I *did* at one time have a radio (an XTS-3000) that would (seemingly randomly) miss certain P25 transmissions... despite quite a lot of effort I could never find out why. I got rid of the radio, never saw it happen again (with any other radio or scanner).

Peter
K1PGV

I have this problem *ALL* the time with my P25 portable but never on my scanners. (weird!) My RS Pro-96 and Uniden BCD396T handheld scanner have no trouble hearing Troop B on 154.935. I used to own a pair of ICOM IC-F70DT P25 portables and they always had trouble hearing B-troop. I'd hear no audio at all or just an occasional syllable or two come through while my scanners always decoded it fine. I later sold the F70DT portables and now own a KENWOOD TK-5210K3 P25 portable and it does the exact same thing!!! P25 traffic on other NHSP freqs decode fine. The KENWOOD P25 portable is far superior to the ICOM portable in many ways and is right up there with the Motorolas, yet they have trouble decoding Troop B's normal P25 voice transmissions while my scanners always decode them fine. From a few reports I've received, I'm not alone in noticing this behavior.

I originally expected a genuine P25 radio to do a better job of decoding P25 audio than my scanners do. It also makes me wonder what kind of problems the officers may be having with their P25 equipment that we haven't heard about.

Back in early 2003 when I first got my Uniden BC250D handheld, I noticed that I had to tweak the P25 sound quality adjustment slightly to hear Troop B perfectly. However, with the BC250D scanner being a battery-hungry piece of crap, the sound quality adjustment applies to the entire band and not to individual channels. I wasn't too surprised given that the BC250D was the first P25-capable scanner on the market. I had to experiment and find a setting that worked well for everything in the VHF band. I used Londonderry PD on 155.865 as a test freq to make the adjustment. B-troop sounded better than it did before but still a little bit robotic and digital sounding. The final adjustment ended up being a compromise. I suspect B-troop's transmitter(s) may be slightly out of alignment compared to a properly aligned P25 transmitter.

 

[jmarcel66]

I've noticed that certain areas I simply don't pick up Troop-B in their response area. I'm not sure if it's a signal problem or other. They do on occasion use encryption. And typically dispatchers don't use it. It does seem though that their signal doesn't get out like the other troops do.

When you hear troopers refer to "Troop Talk" that is the simplex ops on the repeater output.

 

[n1das]

I'm not sure if it's a signal problem or other.

I think it's an "other" type of problem. In the Nashua area, the signal strength is very strong. My Pro-96 and BCD396T scanners receive it and decode it beautifully all the time. It's my KENWOOD P25 portable (TK-5210, K3 version) that has trouble EXACTLY like my ICOM F70DT portables did. I've done several side by side tests to confirm it. The scanners hear it fine while my genuine P25-compliant portable absolutely won't decode it or I sometimes get at most a syllable or two coming through. I expected the P25 portable to outperform my scanners in this area but this is clearly not the case. It's not a NAC issue either because I'm using the $F7E "digital carrier squelch" NAC in the KENWOOD portable.

I'm also wondering if its due to multipath effects from simulcasting from different sites. IIRC, Troop B simulcasts from two locations, correct? (If so, from where?)

 

[jmarcel66]

It's my KENWOOD P25 portable (TK-5210, K3 version) that has trouble EXACTLY like my ICOM F70DT portables did.

I've heard that the Kenwood's have been having a hard time decoding some of the Motorola radios (what NHSP uses). Up here, the K/W's reportedly can't receive the Concord Police System. My reception issues have been w/the Pro-96 and BCD296 scanners. If I remember, when I had a P25 M/A-Com for a bit, it picked up Troop-B great in Penacook/Concord. But not so great in Merrimack on the Everett.

 

[PeterGV]

I originally expected a genuine P25 radio to do a better job of decoding P25 audio than my scanners do. It also makes me wonder what kind of problems the officers may be having with their P25 equipment that we haven't heard about.

Well... It WAS just one unusual XTS3000 that had this problem. For what it's worth, both my XTS2500 and XTS5000 do a masterful job of decoding Troop B (and every other mongrel X25 channel I've tried to listen to). It could have been the firmware revision... As I understand it, there aren't many conventional systems in the US that have both voice and data on the same channel.

The data is "MDT" data in TCP/IP format.

There was a brief article in "Law Officer" magazine a couple of years ago about Project 54: http://www.policeone.com/writers/columnists/lom/articles/134974/

There was a recent article, also, in... ah.. hmmm... Critical Communications (formerly MRT), I think.

Lots of good (detailed) info on the system available by the project's homepage:

http://www.project54.unh.edu/

Peter
K1PGV

 

[tmcmath]

Troop B has always been diificult at times to hear. They do use data on the same frequency but they also appear to use several different repeater sites also. I live in Merrimack and hear them clearly most of the time unless they are tranmitting to units over on 93 between the MA line up to about the 293 split. It seems like whenever they are out on 293 or the Everett Turnpike they come in well. It's spotty on 93 and also on 101 west of 93 beyond Bedford. I also get the same results with NHSP headquarters (troop D) on 156.21 but that maybe the distance I am from Concord. I hear troop A,E, and C fine with no issues. I never hear troop F though.

 

[jmarcel66]

Troop B has always been diificult at times to hear. They do use data on the same frequency but they also appear to use several different repeater sites also. I live in Merrimack and hear them clearly most of the time unless they are tranmitting to units over on 93 between the MA line up to about the 293 split. It seems like whenever they are out on 293 or the Everett Turnpike they come in well. It's spotty on 93 and also on 101 west of 93 beyond Bedford. I also get the same results with NHSP headquarters (troop D) on 156.21 but that maybe the distance I am from Concord. I hear troop A,E, and C fine with no issues. I never hear troop F though.

That's the weird part. It should be a simulcast system so no matter where you are (when stationary anyway) the signal should always be the same. They may have had to goto the same system Troop-F uses selecting sites.

 

[fog]

Sorry to bring this back. I'd assumed that they just didn't have a strong signal into Merrimack. But I happened across 154.935 on a ham HT (scanning the band) and noticed that they have an S9+ signal.

Has anyone had luck monitoring them? Besides feeling like I'm missing some comms, I'm finding that the scanner (Pro96) constantly stops on digital noise, which I assume to be the MDTs they use. It's irritating enough that I tend to keep them locked out. Just wondering how others deal with this.

 

[PeterGV]

As previously mentioned, I dealt with this and ALL the various, annoying, issues related to poor P25 decoding, by buying a few Motorola XTS-series radios (2500, 3000, 5000).

It's the only way I know of to solve the problems of monitoring P25 conventional channels in Southern New Hampshire. I wrote a bit about this topic on my web site: http://www.k1pgv.com/VUS.html

Peter
K1PGV

 

[fog]

That's one way of doing it. Maybe I shouldn't have sold my VHF ASTRO Saber.

 

[n1das]

As previously mentioned, I dealt with this and ALL the various, annoying, issues related to poor P25 decoding, by buying a few Motorola XTS-series radios (2500, 3000, 5000).

It's the only way I know of to solve the problems of monitoring P25 conventional channels in Southern New Hampshire. I wrote a bit about this topic on my web site: http://www.k1pgv.com/VUS.html

Peter
K1PGV

I've had exactly the opposite experience with Troop B's signal on 154.935MHz. I have no trouble at all decoding Troop B's P25 signal on my P25 scanners. I've only had trouble decoding their signal on my P25 handhelds and ONLY on B-Troop's signal. My P25 handhelds (Icom F70DT...sold a while ago, now have a Kenwood TK-5210) otherwise have no trouble decoding P25 traffic on other frequencies in Southern NH....I've only had trouble with Troop B's signal.

It's not a signal strength issue in the Nashua NH area...I get it full scale here on my scanners and P25 portable (S-meter not calibrated, only a relative reading). I've never had troubles due to weak signal strength. I think "B" has a misaligned transmitter and Moto XTS-series portables like my scanners maybe are a bit more tolerant of digital errors. Works with some radios but not others. YMMV.

The other reason I suspect "B" might have a misaligned transmitter is that back in 2003 when I got one of the first Uniden BC-250D handheld scanners (first P25 scanner by Uniden), I found I needed to tweak the P25 quality adjustment slightly to get "B" to sound right. Unfortunately the adjustment affects all P25 traffic heard in the same band and it threw the adjustment slightly off on all other VHF freqs. Uniden hadn't thought of making the P25 quality setting adjustable on a per channel basis yet. I ended up having to tweak it back to where all the other P25 stuff was good and "B" ended up being the only one that sounded slightly off. Although it often produced bad P25 audio from "B" but at least it decoded reliably.

 

[PeterGV]

<QUOTE>
I think "B" has a misaligned transmitter
</QUOTE>

Interesting idea, David... By "misaligned", do you mean "off frequency", "improperly deviating", or something else? Sorry if that's a dumb question.

I don't think ANY scanner would mind a carrier slightly off frequency, as I think they ALL compensate for this and center on the ACTUAL frequency (as opposed to the programmed frequency). I'll be happy to check Troop B's signal with my spectrum analyzer to get some further data, if you think that'd be helpful.

Aside from that... how do you like your TK-5210?? (that's a serious question, I considered buying one). Can you describe in what way(s) it doesn't decode Troop B well? Just broken-up audio, or do you get the ever popular "hang on channel but no audio received" problem? Because the latter I'd chalk-up to their charming in-band data use. How well does it decode Hillsborough County?

Peter
K1PGV

 

[Sinister]

I have noticed something strange about recieving the state police. I tried setting my mod from FM to Auto leaving the squelch mod to NAC and squelch code to 826 and seems like I got spotty results so I just use FM and leave the rest as is and I recieve them just fine. I have heard Troop A, B, D loud and clear although there is occassionally the strong signal without any audio for troop B.
Scannner used is the PSR 600.

 

[n1das]

<QUOTE>
I think "B" has a misaligned transmitter
</QUOTE>

Interesting idea, David... By "misaligned", do you mean "off frequency", "improperly deviating", or something else? Sorry if that's a dumb question.

Hi,

Not a dumb question at all! I think it's an "improperly deviating" type of problem and not anything to do with data on the same freq It's P25 voice data that's not being decoded properly. From what I've been told by a radio tech is that a P25 transmitter has to be set up correctly such that the deviation has to be correct in all 4 quadrants. You won't be able to see this by looking at the signal on a conventional spectrum analyer since it has to do with the phase relationship between individual symbols in the P25 data.

My symptoms on the TK-5210 are simply no P25 decode at all and the radio remains muted even though it's programmed for NAC F7E, i.e., unmute on any incoming NAC. It's definitely not a NAC problem. I previously owned a pair of ICOM IC-F70DT P25 portables and they both did the same thing on B's signal and I would get at most a few syllables of decoded audio. I also know someone who has an EFJohnson P25 and a Midland P25 portable and they both do the exact same thing on Troop B's signal and he also hears Troop B perfectly on his P25 scanners.

Aside from that... how do you like your TK-5210?? (that's a serious question, I considered buying one). Can you describe in what way(s) it doesn't decode Troop B well? Just broken-up audio, or do you get the ever popular "hang on channel but no audio received" problem? Because the latter I'd chalk-up to their charming in-band data use. How well does it decode Hillsborough County?

Peter
K1PGV

I haven't tried it yet on Hillsboro County yet but maybe I should since I live in Hillsborough County, LOL.

My symptoms are no P25 decode at all on B's signal when somebody is talking. I've confirmed it several times on my scanners....the scanners all hear it while the 5210 stays muted. The 5210 doesn't hang on the channel...it correctly ignores the other non-voice data....just stays muted on legit P25 audio traffic.

The one weird thing about listening on my scanners is that my BC250D portable (what a POS!) behaves like the sound quality adjustment needs a slight tweak to hear Troop B's signal better. The sound quality adjustment on the 250D is a manual adjustment and the adjustment affects decoding all P25 traffic in the same band. Uniden got smarter in their newer scanners by making it automatic with the option of manually adjusting it on a per channel basis. The fact that Troop B's signal needs a slight tweak while all others are OK for a given quality setting leads me to believe that some of the modulation parameters may be slightly out of whack with Troop B's transmitter.

As for how I like the 5210....I absolutely LOVE it! It is definitely WAAAYYYY better than the ICOM F70DT portables I had previously....better in every way including audio and battery life. Overall the 5210 is right up there with the Moto XTS's in terms of overall quality. It's a bit more pricey than the ICOM but less than the Motos. I would recommend it as an option to consider if looking for an alternative to Motorola.

The only weirdness I've run into is the failure to decode Troop B's signal and ONLY Troop B's signal so far. All other P25 traffic I've heard on it decodes perfectly and better than any of my scanners. I've also played around with P25 on the 2-meter ham band and it works well there.