IDAS (NXDN) network monitoring

[Eaton]

Hi All!
One of our rural police departments has switched to the IDAS (NXDN) conventional. Since there's no scanner to monitor such digital mode yet, I decided to pick up an Icom F3101D portable to listen to this system.

This format is totally new to me. I've done some googling on this topic, but got just a little info and no answers to the questions I'm concerned about. NXDN is very similar to the MotoTRBO, I guess, but in DMR only tuning to the desired frequency will not enable one to listen to the traffic - one will need to know TG ID, color code, repeater slot as well.

I suspect that NXDN requires some key parameters, except for the frequency, that are needed to listen to the voice traffic. But how to obtain them? With MotoTRBO, I used DMRDecode or a similar tool to work out TG and coluour code info...

So, the questions:

1. What are the main points I need to monitor the NXDN voice traffic?
2. Is there a "wildcard" TGID that will enable the radio to receive any digital voice on a particular channel (like F7E NAC on P25)?
3. Is there a software tool to scout the NXDN traffic?

That's all, at least for the time being.
Thanks to everybody in advance!

 

[TheWizard]

You're making it seem more complicated than it is. The NXDN format is much simpler to program than a DMR.

You will need the frequency you wish to monitor, set it to digital as channel type.

Leave the RAN (Similar to NAC) disabled, and you'll hear everything, unless it's trunked or encrypted, then there are other issues.

Now, there is a 12.5Khz and 6.25Khz type of NXDN. Only the kenwood radios support the 12.5. Icom radios are only compliant with Kenwood only on "ultra narrow" -or- 6.25Khz mode. If the agency you wish to listen into is using all Kenwood equipment, then they may or may not be using 6.25Khz. However, with brand compatibility issues, and how 6.25 is more efficient- and for some reason, works better than the 12.5, I don't see why anyone would want to use it.

 

[120Comm]

but seeing as how it's more spectrally efficient and works longer range than the 12.5, I don't see why anyone would want to use it.

Um... typo? Otherwise, unless sarcasm, I'm confused.

 

[TheWizard]

Let's be real, when I typed that I'd just gotten up for the day and waking up.

My point is that the 6.25Khz AMBE, for whatever reason works better than the 12.5Khz.

Back when I first got a pair of Kenwood NX700 mobiles back in 2010, I set up one on my home base antenna connected to a recorder. I put the other in the car and drove out to various spots and tested 25Khz analog, 12.5Khz analog, 12.5Khz NXDN and 6.25Khz NXDN. I found at least one location where 12.5Khz analog was faint at best, and 12.5Khz NXDN was high in BER, but I'll be damned if the 6.25khz cut through the crap and came in pretty great. I was mobile, but stationary during the testing and while highly unscientific, it sold me on the "ultra narrow band" mode.

Unless there was something else you were referring to that wasn't clear. I certainly wasn't trying to throw in marketing hype.

 

[Eaton]

TheWizard, thank you for the fast and thorough reply!
In the following messages I wanted to ask what RAN is but you answered even my unspoken question!

When I read that "NXDN competes with DMR" I thought that these formats were really similar though non backward-compatible.

The department I want to monitor sticks to the Icom gear, that's why I picked up an Icom radio for monitoring. I don't think they use encryption because any foreign encryption algo must be type accepted to be legal to use in our country and it happens really rarely.

Interesting thing, when they did analog they were heard very far away, but when IDAS was adopted, the coverage decreased drastically.

I will try programming my radio and update the thread.

 

[120Comm]

I found at least one location where 12.5Khz analog was faint at best, and 12.5Khz NXDN was high in BER, but I'll be damned if the 6.25khz cut through the crap and came in pretty great. I was mobile, but stationary during the testing and while highly unscientific, it sold me on the "ultra narrow band" mode.

Unless there was something else you were referring to that wasn't clear. I certainly wasn't trying to throw in marketing hype.

I guess I misunderstood your original post. "I don't see why anyone would want to use it" implies to me that you don't think people should use 6.25.

 

[Eaton]

Here's the update.

I've found and programmed some NXDN channels into my radio. They are set as digital-only, RAN is set to 0, squelch is set to OFF, encryption to OFF.

But for some reason I can't hear the audio. The radio's LED lights up green indicating that the channel is busy but no talks can be heard. Pressing and holding the monitor key never helps either.

BTW, here's what I have on the analog receiver:
View attachment RecordingIDAS - 2013.09.01 - 22.43.24.wav

I can post or mail my codeplug if anyone can look at it and find out what is wrong.

Any help is greatly appreciated!

 

[TheWizard]

That doesn't really sound like NXDN to me, either that or the recovered signal is weak/staticy. Anyhow, this audio file from the internet http://www.w2sjw.com/sounds/NXDN_multi.mp3 has some samples of the data stream through an analog receiver. What you're hearing sounds like something else... perhaps MDTs?

 

[Mars]

Eaton: That signal almost sounds as if it's being received off-frequency. Are you positive you're centered? Very critical with these narrowband systems.

 

[Eaton]

I'm 95 percent positive that the signal I'm trying to decode is NXDN. First, I'm monitoring to the department that was reported as a first user of IDAS in the special communications magazine. Second, the data stream I hear is exactly the same as in your sample from w2sjw. Maybe that's because I used poor software for sound recording or the sound of the receiver was too loud. If you try to listen to my recording again but turn the volume down you'll probably see some similarities.

However, the point about the weak signal really makes sense! First, the agency is situated way across the region (more than 40 miles from my place). Second, I tried programming my radio for mixed-mode operation and it picks up this signal as if not digital-enabled, I hear the digital noise only, it never tries to decode this stream.

What confuses me is that the Uniden scanner displays 2 of 5 RSSI bars for this signal. Thus, I assume that the transmission is strong enough to be decoded (or at least recognised by the radio as digital, judging by my ASTRO25 experience)

The bottom line for me is to try getting closer to the agency which uses this channel.

BTW when I programmed my Icom I noticed that the default RAN is set to 1. Shall I change it to 0 to disable the RAN or is it enough to set the squelch setting to OFF?

Thank you for your hepful posts!
Alex

 

[Eaton]

2 Mars:
the freq was found with the Uniden scanner, search step is set to 12.5.
Again, the distortion is my or software's fault, in reality it is pretty much like the sample. I even tried transmitting digital with my radio to check out how it sounds

 

[Mars]

10-4. Good luck on decoding. I want to start playing with NXDN/IDAS stuff this winter. Unfortunately for me, DSD doesn't do jack ****. I'm going to have to get a portable or two I remember how fun it was when I first starting flirting with TRBO on weak signals and "can't be scanned" users

 

[TheWizard]

Good luck, I hope you can get better results by being a bit closer/taking a visit to the area.

Second, DSD is a great piece of software, but it is almost useless when the signal isn't nearly full-quieting. A lot of software is this way unfortunately.

 

[Eaton]

Hi there!
Sorry for bringing it back to life, but it really took me almost a year to get to this (I wasn't trying hard though, I must admit it )

First thing, our policemen are using Icoms and Icoms can only do 6.25 KHz channel spacing - that's why if one tries to monitor an Icom IDAS system with a Kenwood radio only Very Narrow channel spacing should be used. Otherwise, the radio will stop scanning on a given channel if the signal is present but no audio or signalling can be detected.

Secondly, when hunting for the frequencies with a scanner, it is important to set a correct step. For Icom system, 6.25 KHz should be used. If the frequency is not accurate, you can still hear the digital rumbling on the analog receiver, but it may not decode on an NXDN/IDAS radio.

The bottom line for monitoring unfamiliar NXDN/IDAS system is:
1. Set the scanner step properly - you will want 6.25 KHz
2. Set the channel spacing of your radio accordingly. If you're not sure, program 2 different channels with both variants and set them to scan.
3. Set RAN to 0.
4. Set squelch to OFF.
5. Make sure the system in question is not encrypted or trunked (however I heard rumors that only Icom radios bloch trunked channels from being received in conventional mode, can anyone prove this?)

I hope my experience will be useful to anyone in future.

Guess this thread will be more use in NXDN/IDAS forum

 

[ppcradioman]

"When I read that "NXDN competes with DMR" I thought that these formats were really similar though non backward-compatible."

NXDN/IDAS is FDMA; DMR is TDMA; other than being digital formats they have nothing in common.

 

[Eaton]

Why? NXDN uses AMBE vocoder just like DMR. It appears that they sound quite similar. I agree that they use different channel division though.

I was told that radios operating on 12.5 KHz use 9600 bps bitrate while 6.25 ones transmit at 4800.
Is it really true?

 

[kc0wkp]

Yes the 4800\6.25 and 9600\12.5 is true. How ever most, not all, NXDN trunking systems are 6.25. ICOM has just released the IC-F3261D which will work on both the Kenwood Control Channel trunking and ICOM's IDAS Logic based trunking.