NXDN 6.25khz frequency stability

[swwifty]

I'm curious what other experiences are with 6.25khz (very narrow) NXDN.

I recently noticed that some radios sound better than others on 6.25khz NXDN. Mainly, some radios are seriously garbled when running 6.25 vs other radios of the same make and model. I think this might have a lot to do with portables drifting off frequency, or the repeaters drifting.

I imagine since 6.25khz is so narrow, it doesn't take much drift to cause issues.

Has anyone experienced this? Kenwood seems to claim you don't need a high stability oscillator for their repeaters when running 6.25khz, which I find hard to believe.

 

[Project25_MASTR]

You don't need a high stability oscillator. The front end of NX series subscribers isn't actually selective enough to allow for two adjacent 6.25 kHz channels in a 12.5 kHz span of spectrum (contrary to one of the common selling points of 6.25 kHz NXDN that Kenwood uses). While you could have issues with drifting issues you could also have issues with mismatched firmware and/or DSP improvements that comes alone with later firmware.

 

[swwifty]

You don't need a high stability oscillator. The front end of NX series subscribers isn't actually selective enough to allow for two adjacent 6.25 kHz channels in a 12.5 kHz span of spectrum (contrary to one of the common selling points of 6.25 kHz NXDN that Kenwood uses). While you could have issues with drifting issues you could also have issues with mismatched firmware and/or DSP improvements that comes alone with later firmware.

Good point on the firmware issues. I'd have to check and confirm, but I know some of the radios i've heard over NXDN have pretty old firmware.

 

[mmckenna]

Kenwood does not -require- a high stability reference for 6.25KHz narrow, but they do recommend it for the repeaters if running in very narrow (6.25kHz mode).

Older radios wandering too far off frequency when running 6.25KHz mode can be an issue. It would be worth putting the offending radios on the service monitor to see where they are.
I run my trunked system in the 12.5KHz mode, and haven't had any issues with it. I have heard of others having issues with 6.25 as the radios age.

I'd compare firmware version also, between the good and bad radios. Really easy to update firmware on these radios.

 

[swwifty]

Kenwood does not -require- a high stability reference for 6.25KHz narrow, but they do recommend it for the repeaters if running in very narrow (6.25kHz mode).

Older radios wandering too far off frequency when running 6.25KHz mode can be an issue. It would be worth putting the offending radios on the service monitor to see where they are.
I run my trunked system in the 12.5KHz mode, and haven't had any issues with it. I have heard of others having issues with 6.25 as the radios age.

I'd compare firmware version also, between the good and bad radios. Really easy to update firmware on these radios.

Good info, thanks for the reply. It seems like the repeater would need the high stability reference, or at least have it aligned frequently.

 

[mmckenna]

or at least have it aligned frequently.

Mine have been running since 2011 and I haven't had any issues with them. NXR-900's and only in 12.5KHz mode, but they still test just fine.

 

[AM909]

It would seem that the repeater, usually in a relatively controlled environment, and running 24x7, would actually be less likely to need an HSO than subscribers that get bounced around in widely variable conditions. Given similar designs, if the repeater and the subscribers both drift downward at similar low rates, the only reason to reset them will be when they move too far into the adjacent channel.

 

[mmckenna]

It would seem that the repeater, usually in a relatively controlled environment, and running 24x7, would actually be less likely to need an HSO than subscribers that get bounced around in widely variable conditions. Given similar designs, if the repeater and the subscribers both drift downward at similar low rates, the only reason to reset them will be when they move too far into the adjacent channel.

If one subscriber wanders off frequency, it's one subscriber.
If the repeater wanders off frequency, it's ALL the subscribers.

I run all our radios through auto alignment whenever they are here in our shop. I do have many that are almost 13 years old that have never been touched and are still running well. But I'm running 12.5KHz, so a bit of slop room.

 

[slicerwizard]

The front end of NX series subscribers isn't actually selective enough to allow for two adjacent 6.25 kHz channels in a 12.5 kHz span of spectrum

Pretty sure you've also made this claim in the past. Meanwhile, this site just keeps on trucking:


OnQue Site 1 Toronto (CN Tower)

NEXEDGE48 202 1 34 422.20000
NEXEDGE48 202 1 35 422.20625
NEXEDGE48 202 1 36 422.21250

NEXEDGE48 202 1 40 422.23750

NEXEDGE48 202 1 45 422.30000
NEXEDGE48 202 1 46 422.30625
NEXEDGE48 202 1 47 422.31250

NEXEDGE48 202 1 50 422.33750

NEXEDGE48 202 1 55 422.40000
NEXEDGE48 202 1 56 422.40625
NEXEDGE48 202 1 57 422.41250

NEXEDGE48 202 1 61 422.43750

NEXEDGE48 202 1 66 422.50000
NEXEDGE48 202 1 67 422.50625
NEXEDGE48 202 1 68 422.51250

NEXEDGE48 202 1 71 422.53750

NEXEDGE48 202 1 76 422.60000
NEXEDGE48 202 1 77 422.60625
NEXEDGE48 202 1 78 422.61250

NEXEDGE48 202 1 82 422.63750

 

[Project25_MASTR]

Pretty sure you've also made this claim in the past. Meanwhile, this site just keeps on trucking:


OnQue Site 1 Toronto (CN Tower)

NEXEDGE48 202 1 34 422.20000
NEXEDGE48 202 1 35 422.20625
NEXEDGE48 202 1 36 422.21250

NEXEDGE48 202 1 40 422.23750

NEXEDGE48 202 1 45 422.30000
NEXEDGE48 202 1 46 422.30625
NEXEDGE48 202 1 47 422.31250

NEXEDGE48 202 1 50 422.33750

NEXEDGE48 202 1 55 422.40000
NEXEDGE48 202 1 56 422.40625
NEXEDGE48 202 1 57 422.41250

NEXEDGE48 202 1 61 422.43750

NEXEDGE48 202 1 66 422.50000
NEXEDGE48 202 1 67 422.50625
NEXEDGE48 202 1 68 422.51250

NEXEDGE48 202 1 71 422.53750

NEXEDGE48 202 1 76 422.60000
NEXEDGE48 202 1 77 422.60625
NEXEDGE48 202 1 78 422.61250

NEXEDGE48 202 1 82 422.63750

The difference is my info is coming from JKUSA internal documents from 2017 but it primarily relates to the NX-3000's SoC design as that was the SU that was extensively tested in the document but is also overall (in the US at least) the most popular NXDN solution.

 

[phillmobile]

defo need a 10mhz ocxo on a very narrow trunk system, it also allows the repeaters to synchronize for timing too

 

[swwifty]

defo need a 10mhz ocxo on a very narrow trunk system, it also allows the repeaters to synchronize for timing too

what about a conventional system?

 

[mmckenna]

what about a conventional system?

Keeping a conventional NXDN 6.25KHz system on frequency is just as important.

 

[swwifty]

Keeping a conventional NXDN 6.25KHz system on frequency is just as important.

I assumed so, was just wondering your thoughts. Thanks.

 

[mmckenna]

I assumed so, was just wondering your thoughts. Thanks.

No problem.

The frequency reference in/out on the repeaters is different than the Sync in/out on the repeaters. The sync is used in trunking systems.

The frequency reference in/out can use an internal oscillator that Kenwood sells, or an external one.

 

[fontanei]

I have been using icom idas (same thing as NXDN 6.25Khz) and they have always sounded garbled. Not very clear at all compared to P25. I would stay away from 6.25Khz BW modes if voice clarity is imperative.

Never heard nxdn 12.5Khz; however, I bet it sounds much better since there is more BW to send data (digitized voice).

 

[swwifty]

I have been using icom idas (same thing as NXDN 6.25Khz) and they have always sounded garbled. Not very clear at all compared to P25. I would stay away from 6.25Khz BW modes if voice clarity is imperative.

Never heard nxdn 12.5Khz; however, I bet it sounds much better since there is more BW to send data (digitized voice).

This is my experience as well, hence this thread.

I've played around with 12.5khz NXDN and it sounds a lot better