Garbled P25 audio

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n7lxi

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Hi all, I have a PSR-500 and 95% of the time, the audio is as good as my Moto XTS5000 at work.

However, every now and then I get totally garbled audio. This is not the same "digital break up" I hear when using my radio at work, not the typical stuttering and choppy sound. I'm curious if this garbled audio is inherent in the P25 scanners or if it's an antenna issue, maybe the loss of decent signal. I'm using the rubber duck in the house, and as I said 95% of the time it's perfect. I guess I was just hoping for 100%.

Also, I'm monitoring the Delaware statewide TRS, mostly Sussex Fire and EMS.
 

N1BHH

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Jackson Square, East Weymouth, MA.
Hi all, I have a PSR-500 and 95% of the time, the audio is as good as my Moto XTS5000 at work.

However, every now and then I get totally garbled audio. This is not the same "digital break up" I hear when using my radio at work, not the typical stuttering and choppy sound. I'm curious if this garbled audio is inherent in the P25 scanners or if it's an antenna issue, maybe the loss of decent signal. I'm using the rubber duck in the house, and as I said 95% of the time it's perfect. I guess I was just hoping for 100%.

Also, I'm monitoring the Delaware statewide TRS, mostly Sussex Fire and EMS.
Your scanner is designed to scan a wide range of frequencies and is broadband as compared to a single band radio. There are times the scanner outshines the XTS and that's because it can hold more objects to scan. You can also be in a slight different location and experiencing multi-path conditions when receiving signals, especially P-25 transmissions.
 

n7lxi

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The Garbled audio could very well be encripted voice... I get it on my local PD all the time...
It's most definitely not encrypted audio. I use these radios at work and know for a fact that these talkgroups are not encrypted.

It does have the “wooshy” sound of multipath, but it's totally unintelligible. And it'll usually be a transmission in the middle of a conversation. However, the other unit hears fine, because they'll answer or continue the conversation, so it's not the portable on the fringe of coverage of the tower. It's between the tower and me. Oh well. Maybe an outdoor antenna will help.
 

ScannerSK

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Gilcrest, CO
There is a known issue here in Northern Colorado with our P25 system in which conversations entering 700 MHz towers which are then relayed out 800 MHz towers creates hard dropouts during conversations noticeable on scanners (not on professional radios). Do you have 700 MHz towers in use in your area?

There are a few key characteristics of this issue in Colorado:
1.) It sounds like half second to second long chunks of audio being chopped out of conversations.
2.) The chunks of audio only disappear from the transmissions of non-dispatch units. In other words, the problem does NOT affect dispatch transmissions.
3.) The chunks of missing audio do not affect professional radios in the field as other professional units copy the transmissions without difficulty.

The fact that this issue does not occur when dispatch is talking and that it does not affect professional radios in the field leads me believe it is an issue with the decoding capabilities of the PSR-500/600 scanners. The issue is believed to be linked to the 700 MHz towers as only transmissions from units in the Southern part of our large county (Weld) create this issue which is where the 700 MHz towers are located. Also, the issue began around the time the 700 MHz towers began to be used in this area.

I am unaware of whether the problem is experienced on all P25 scanners or only on GRE's scanners?

Shawn
 
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RomeRon

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Rome Ga.
Hi all, I have a PSR-500 and 95% of the time, the audio is as good as my Moto XTS5000 at work.

However, every now and then I get totally garbled audio. This is not the same "digital break up" I hear when using my radio at work, not the typical stuttering and choppy sound. I'm curious if this garbled audio is inherent in the P25 scanners or if it's an antenna issue, maybe the loss of decent signal. I'm using the rubber duck in the house, and as I said 95% of the time it's perfect. I guess I was just hoping for 100%.

Also, I'm monitoring the Delaware statewide TRS, mostly Sussex Fire and EMS.
Does it sound like this?
http://www.w2sjw.com/sounds/DES Decoded.mp3
 

K4IHS

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Charlotte, NC
Go outside... or try your radio closer to the source tower. If that makes it better... get a good outside antenna.
 

04Z1V6

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Castle Rock, Co.
Wow sounds like a great system. Reading the state wide page it seems like it has a lot of different systems that work together. There are allot of encrypted TG's in the system make sure you don't have those programmed and the way it reads you need to be ready for changes as they finish building the system.
 

fourthhorseman

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So Far Away....
im not the O-P
but yeah,i get that here in philadelphia,PA,been puzzled about this or a couple years now..


i do notice the dispatchers Will ask a user to repeat,quote,"you came across garbled,please repeat your message"
but i cannot recall users ever having that issue with dispatch,,the console seems to TX clear..only the mobile/portables are effected..
 

Ed_Seedhouse

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Victoria B.C. Canada
On the Crest system here in Victoria B.C. this happens and the dispatchers ask the callers to repeat transmissions, saying they got "bonked". There is an article in the latest issue of "Monitoring Times" that has a good explanation of why this can happen. P25 sends in "packets" and if the packets get scrambled by noise this can happen. Narrow bandwidth digital is more vulnerable to this effect because it has less room in each packet for error correction code. The mobile units being low power are obviously going to be more susceptible to noise than the main high power transmitters the dispatchers will be using.
 

n7lxi

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Lancaster PA
We refer to the packet loss here as "going digital", as in "Medic 104, can you repeat, you went digital".

However, again... This is not the typical packet loss sound that I hear on an XTS5k. Does it just sound different on a scanner? I'll try and record some samples in the next day or two.


Sent from my iPhone.
 

n7lxi

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Well, I stand corrected. The garbled audio sounds identical to the encrypted audio on the sample page.

I think I now know why. The radios have the encryption option on the concentric switch, but we never use it. However, some may have bumped the switch and not noticed. The system is set up so if your radio receives encrypted audio, it's heard unencrypted, but unless you select encrypt, you'll transmit in the clear.

Thanks for the help.


Sent from my iPhone.
 

Eickerman

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I think I now know why. The radios have the encryption option on the concentric switch, but we never use it. However, some may have bumped the switch and not noticed. The system is set up so if your radio receives encrypted audio, it's heard unencrypted, but unless you select encrypt, you'll transmit in the clear.
This is, indeed, how encryption works. Any radio containing encryption keys will automatically decrypt a transmission regardless of whether the radio has encryption turned on or off. However it will only send encrypted if the switch is turned on.

Locally I've caught a couple of times when an officer accidentally has encryption on while dispatch and everyone else is not encrypted. Dispatch never realizes this because they hear it fine so it never triggers dispatch to have the officers fix the problem (which for dispatch is not a problem ).

This does illustrate a potential security hole. If someone is supposed to be transmitting encrypted, but isn't, no one with the encryption keys ever notices that they have a security issue.

Curtis
 

n7lxi

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Lancaster PA
Okay... here's a follow up. I found out that only certain talk groups have encryption, not the talk group where I heard the garbled audio today.

As a matter of fact, while listening to a paramedic talk to the dispatcher today, I heard clean clear audio, then it became garbled and then it cleared again.
 

markab

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Aug 25, 2005
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Cambridge, Ontario, Canada
Bandplan

Okay... here's a follow up. I found out that only certain talk groups have encryption, not the talk group where I heard the garbled audio today.

As a matter of fact, while listening to a paramedic talk to the dispatcher today, I heard clean clear audio, then it became garbled and then it cleared again.
Hi n71lxi,
I had a very similar problem to the one you described. I know I have a fair bit of stray RFI in my neighbourhood and knowing that the 500 has a hot front end I just figured that it was intermittently overloading the scanner. Last night I was poking around in the scanners settings and realized that my bandplan was set to US. As I live in Canada I set it to Canada. Well I've only been monitoring my scanner for about 1 hour so far but I've had 0 garbled P25 transmittions since, where as before 10-20% were garbled. It may have nothing to do with your problem but it's probably worth looking into.

Mark
 

grecomrr

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Sep 22, 2011
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atomicsedu@yahoo.com
Radio Shack 20-283

Hi all, I have a PSR-500 and 95% of the time, the audio is as good as my Moto XTS5000 at work.

However, every now and then I get totally garbled audio. This is not the same "digital break up" I hear when using my radio at work, not the typical stuttering and choppy sound. I'm curious if this garbled audio is inherent in the P25 scanners or if it's an antenna issue, maybe the loss of decent signal. I'm using the rubber duck in the house, and as I said 95% of the time it's perfect. I guess I was just hoping for 100%.

Also, I'm monitoring the Delaware statewide TRS, mostly Sussex Fire and EMS.
The RS 20-283 antenna stopped all my garbled crap on P25 systems
be sure you don't buy the old 20-283 the new one says on package

"specifiably designed to monitor 800mhz trunked radio"


Radio Shack 20-283
 
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