Johnson County P25 System

[MadSpleen85]

A question for those who have knowledge of the actual user radios...

Can one individual radio user switch encryption on/off while on a normally clear TG?

I've noticed some traffic on the Sheriff's Office primary TGs that, at least on my end, sounds encrypted. The deputy's traffic comes across just like encryption would, the dispatcher's traffic is completely in the clear with no distortion.

I don't have any first hand knowledge of these radios or that much in-depth knowledge of this specific system. Just seems like the Sheriff's Office uses a little bit of mixed traffic instead of it all being in the clear on the primary TGs.

 

[PVPD730]

A question for those who have knowledge of the actual user radios...

Can one individual radio user switch encryption on/off while on a normally clear TG?

I've noticed some traffic on the Sheriff's Office primary TGs that, at least on my end, sounds encrypted. The deputy's traffic comes across just like encryption would, the dispatcher's traffic is completely in the clear with no distortion.

I don't have any first hand knowledge of these radios or that much in-depth knowledge of this specific system. Just seems like the Sheriff's Office uses a little bit of mixed traffic instead of it all being in the clear on the primary TGs.

It can be done on some systems depending on how the talkgroups are setup. All the user has to do is push a button or turn a switch to begin transmitting in encrypt mode. KCMO does it quite frequently on their primary dispatch talkgroups. Some channels (such as the regional common talkgroups) will force the radios into clear mode, even if the user forgets to disable their encryption.

 

[KC0CSE]

According to people I know who are privy to the details of the system, 853.9625 is now the sole control channel for the entire Johnson County portion of the system, on every tower, with 853.7750 being the alternate if (and only if) the primary fails.

That having been said, I've been experimenting with programming settings on my 197 and found some slight success in getting better reception by enabling the NFM setting for the system object in Win500. It has reduced a little of the garbling (about 20% collectively), but I'm not certain if it's the sole reason. I recently ran a new antenna cable and replaced the antenna with a better model (the system I primarily use is installed on my truck).

A coworker did have me program a Pro-106 for an OPFD volunteer, and it seemed to do very well with the signal threshold settings I've been using, and had very little issues with garbling or transmission loss. A few weeks later, I tried out the system on a BC396XT with mixed results (I'm not terribly familiar with the Uniden platform, since I own only RS model scanners).

Might try that out and see what happens.

What is "NFM"?? and what does it do?

 

[scannerowner]

NFM, stands for Narroband FM Modulation, it's commonly seen on Uniden scanners.

 

[KC0CSE]

what happens if you activate it?...maybe the simulcast could be better?...have the pro 197&pro106

 

[rankin39]

Ideally, switching to NFM would engage a narrower filter that would limit the f.m. deviation of the signal on both transmit and receive. My understanding is that both varieties of popular scanners, Uniden and GRE, lack any choice of receive filters. To make up for this lack they simply boost the volume of the received signal when you "switch to NFM." This wouldn't materially affect simulcast.

If you ever listen to the dedicated KBI TGs, it is clear that units can select encrypted/unencrypted mode individually. On the other hand, my Leavenworth Co. Emerg. Mgt. talkie can't select encryption at all as far as I know. Obviously, then, these sorts of things are set differently for different agencies/TGs.

Bob, WoNXN

 

[MadSpleen85]

Overland Park and Lenexa seem to be using more mixed encryption on their primary talkgroups. Unless there have been some changes to the system to cause major distortion on a scanner, distortion that sounds exactly like encryption.

Anyone else noticing this? Seems to be most common in the early morning hours, 2-5am. Usually just the officer's side of the traffic is encrypted, dispatch is almost always in the clear.

 

[PVPD730]

Overland Park and Lenexa seem to be using more mixed encryption on their primary talkgroups. Unless there have been some changes to the system to cause major distortion on a scanner, distortion that sounds exactly like encryption.

Anyone else noticing this? Seems to be most common in the early morning hours, 2-5am. Usually just the officer's side of the traffic is encrypted, dispatch is almost always in the clear.

Which model of scanner are you using? If Uniden, "ENC" should appear to verify whether or not encryption is being used. GRE/Radio Shack models won't display anything on mixed-mode (only fully encrypted groups).

 

[factorone]

Ideally, switching to NFM would engage a narrower filter that would limit the f.m. deviation of the signal on both transmit and receive. My understanding is that both varieties of popular scanners, Uniden and GRE, lack any choice of receive filters. To make up for this lack they simply boost the volume of the received signal when you "switch to NFM." This wouldn't materially affect simulcast.

If you ever listen to the dedicated KBI TGs, it is clear that units can select encrypted/unencrypted mode individually. On the other hand, my Leavenworth Co. Emerg. Mgt. talkie can't select encryption at all as far as I know. Obviously, then, these sorts of things are set differently for different agencies/TGs.

Bob, WoNXN

It comes down to programming at the radio level most of the time. I do some programming at our shop as an EFJ dealer, but not much. Everything that I've seen suggests that encryption is done at the radio, and at the radio only. However, I've never been told that certain types of hardware beyond that threshold (gateways, trunking controllers, etc.) can't or don't do encryption on entire talkgroups or for certain radio IDs, so maybe it's possible, but not likely.

So, basically my guess is that it's a programming issue. You can program user radios to automatically engage an encryption key upon selection of a talkgroup and keep it enabled until the user changes to another TG, or you can allow user-selection on demand.

As far as NFM vs. FM goes, this is what I've found digging around:

http://forums.radioreference.com/federal-monitoring-forum/143099-auto-nfm-fm-your-p25-chnnels.html

"...As far as I can tell, the scanner scans as FM or NFM when you program a channel that way. "Auto" does nothing more then set a default mode (FM/NFM/AM) based on what GRE thinks is the standard for that frequency band. It clearly has nothing to do with digital detection since setting a channel to FM or NFM still decodes P25, and notice DG is not a "Modulation" selection...only FM/NFM/AM/Auto. When the FM/NFM discriminator detects a signal above the squelch threshold (by noise measurements which change depending on the bandwidth) it stops the scan. Then it determines if P25 is present or not. If not, and you have that channel programmed as NAC, a logical signal is sent to the CPU to continue scanning. If P25 is detected, the logic switches the audio routing to the P25 decoded audio output (comes from the decoder instead of the discriminator) and you get the decoded digital audio instead of the analog discriminator audio. So if (and I do say if) this is the case, how you have the passband set on the discriminator will determine how optimal the data deviated carrier is detected and decoded. One more thing...the squelch action is different between NFM and FM. This is a sure sign that GRE has two different passbands depending on the mode and not just an "audio boost" on NFM like my Uniden scanners had. I think GRE did it right and the results speak for themselves..."

 

[madengr]

JOCO & KCMO

I assume to receive the KCMO side of this system I'll have to monitor the 851.050 MHz control channel? It is strange that I can't receive it at all in west Overland Park, but the JOCO control channel is strong.

If this is a linked system, why are their separate control channels? I thought simulcast meant the JOCO and KCMO control channels would broadcast the same data, but that's not the case. Using Unitrunker I see nothing but JOCO on it's control channel.

 

[BigC801]

I assume to receive the KCMO side of this system I'll have to monitor the 851.050 MHz control channel? It is strange that I can't receive it at all in west Overland Park, but the JOCO control channel is strong.

If this is a linked system, why are their separate control channels? I thought simulcast meant the JOCO and KCMO control channels would broadcast the same data, but that's not the case. Using Unitrunker I see nothing but JOCO on it's control channel.

KCMO MARRS Control Channel is 851.6000 right now.

 

[madengr]

KCMO MARRS Control Channel is 851.6000 right now.

Thank you. I'm picking it up now.

 

[MadSpleen85]

I'm looking at adding a mobile antenna to my daily driver for use with monitoring this system and a little on KSICS. I don't think I am going to need anything with big gain, as most of my driving is done inside the county. I am just looking to get the antenna outside of the car's metal roof.

Anyone have any suggestions? What works for you?



I've read good reviews on the Larsen 150/450/800. But, I can't really justify a 16.5" whip for 95% 800 band.

Ideally, I will be using a Fender mount L Bracket or trunk lip mount as I am not really interested in adding a hole to my three year old car to gain a ground plane, unless I absolutely have to.

Local PD seems to use something very similar to the Laird Tech TRAB7603, which of course requires a ground plane.

 

[bchappuie]

I just have an NMO mounted 1/4 wave whip. About 5.5 in. or what ever the math for 850mhz. I just cut an old motorola vhf antenna. Works like a champ.

 

[MadSpleen85]

I think I will be going with a Larsen NMOQW800 mounted on a Tram 1252-BNC/1255.

This will be for a retired KHP Crown Vic, so there are already holes for the L bracket to mount and already a hole to run the coax into the interior. I need to clean the hole up to see if the BNC connector will fit through that hole or if I will need to purchase a cable that doesn't have the connector on it already and add it after I run it through the hole.

Anyone have any experience with how KHP runs coax through a Crown Vic interior?

 

[oldsarge]

JOCO Sheriff Dispatching to Cities

The Johnson County Sheriff has been dispatching on their frequencies to the cities of Olathe, Lenexa, and a couple others. You shouldn't hear much on their old trunked frequencies. If you even call 911, you will get the Sheriff instead of the city you are calling from. I can tell the dispatchers get a bit peeved at busy times like fourth of July. So keep your ears tuned to JOCO Sheriff's frequencies.

 

[PVPD730]

The Johnson County Sheriff has been dispatching on their frequencies to the cities of Olathe, Lenexa, and a couple others. You shouldn't hear much on their old trunked frequencies. If you even call 911, you will get the Sheriff instead of the city you are calling from. I can tell the dispatchers get a bit peeved at busy times like fourth of July. So keep your ears tuned to JOCO Sheriff's frequencies.

Leawood, Lenexa, Overland Park, Prairie Village, and Shawnee have their own dispatch centers and 911 operators (separate from the Sheriff's Office). Depending on the location, one may get the JOCO Sheriff's Office initially when dialing 911 from a cell phone (because of how the selective routing works with the regional 911 system), but they just transfer the calls over to the appropriate agency.

JOCO Sheriff only handles dispatch for:
Fairway (North Zone)
Merriam (North Zone)
Mission (North Zone)
Spring Hill (South Zone)
Lake Quivira (North Zone)
Olathe (has their own talkgroups, but dispatched by County)
Gardner (South Zone)
Roeland Park (North Zone)
Westwood (North Zone)

Everything is/has been P25 digital over there since '09. The old Motorola analog system is long gone.

 

[factorone]

I think I will be going with a Larsen NMOQW800 mounted on a Tram 1252-BNC/1255.

This will be for a retired KHP Crown Vic, so there are already holes for the L bracket to mount and already a hole to run the coax into the interior. I need to clean the hole up to see if the BNC connector will fit through that hole or if I will need to purchase a cable that doesn't have the connector on it already and add it after I run it through the hole.

Anyone have any experience with how KHP runs coax through a Crown Vic interior?

Just do like everyone else: pull back the trim a little bit, run the cable behind it, and push the trim back. Granted, from what I've seen on KHP's cars in service now, I don't think their garage put that much finesse into it, but I always made a point to hide it as much as possible.

You can probably run the cable through the factory grommet in the firewall just above the passenger-side kick panel if it's going up front. Otherwise, if it's in the back, just pull the C-post trim off of the passenger side and you should have a straight shot to the trunk through the holes in the lower portion of the pillar near the deck. The holes should be more than large enough to fit the connector through, especially for BNC, as I've managed to get full-sized UHF behemoths in through that channel.

Heck, if you need help installing, look me up. I'm in Merriam now, and can probably just zip on over to Shawnee and assist you.

BW

 

[MadSpleen85]

I just have an NMO mounted 1/4 wave whip. About 5.5 in. or what ever the math for 850mhz. I just cut an old motorola vhf antenna. Works like a champ.

What kind of mount do you use? I was thinking L-bracket but, I am starting to lean towards a trunk lip mount (center of trunk lid, center of the vehicle) might be safer as far as being in parking lots, less sticking out for someone to grab or run into.

I am assuming that being inside the county a unity gain such as the Larsen NMOQW800 would work well.

Shawnee, Lenexa & JoCo Parks PD all use something similar to the Laird Tech TRAB8213. That adds 3dB gain but requires a ground plane, which I wouldn't get from an L-bracket and I would imagine would be a very small ground plane with a lip mount. I prefer this look, less to be damaged but, I don't want to overload the scanner with too much gain. Drilling holes in the body isn't an option for me. I don't want to have to deal with them when it comes to selling the car.

My apologies for all of the questions. Antennas are still pretty alien to me, outside of the discone that is on my home's roof.

 

[MadSpleen85]

Does anyone scan this system with the Uniden HomePartol? If so, what are your results?

Shopping around for a family member that lives in the county but does quite a bit of traveling and doesn't want to hassle with programming before every road trip.