436 HP Automatic

[436isthe1]

I have a NXDN system in my Uniden 436 hp, what modulation do I select? Sentinel has it set at Auto. Would I select AUTO, FM ,NFM WFM?

 

[jonwienke]

Auto is going to be NFM in most bands. Some NXDN is actually half the bandwidth of NFM (6.25 vs 12.5 KHz).

 

[Ubbe]

The 6,25KHz systems in NXDN and DMR are just on the brink of being decoded in my Uniden scanners but 90% of the times they are not. Uniden suggested using 25KHz FM mode instead of NFM to improve decoding quality so they might have changed the firmware in the latest releases to lower the signal level in the decoding DSP to adapt to that needed lower signal level. But that doesn't work so well with SFM signals at 6,25Khz. I can only hope that firmware development will continue and add a "fake" SFM 6,25Khz mode that uses a higher signal level at the DSP as more 6,25KHz systems are starting to apperar.

/Ubbe

 

[jonwienke]

There is no such thing as 6.25 KHz DMR. DMR is TDMA, not FDMA.

 

[Ubbe]

A lot of ships have started using 6,25 channel bandwidth in their DMR systems that the Uniden scanners can't really handle.
I have a local channel that use 6,25Khz with mixed analog, DMR and NXDN that are really difficult for Uniden scanners to make them switch and then start to decode from analog to digital mode. It will need more audio level into the DSP to make that work.

/Ubbe

 

[jonwienke]

I've read the DMR spec, and saw no mention of any 6.25 KHz mode. Who makes it?

 

[Ubbe]

Who makes it?

I don't know but almost every ship here the last two years have gone to 6,25KHz super narrow modulation DMR with 6,25KHz channel steps as well.

/Ubbe

 

[racingfan360]

When Uniden first released the beta versions of the BCDx36HP firmware to handle DMR simplex it had a lot of problems tied into how the internal filters worked: it relied on FM being selected vs NFM. I'm not sure they ever changed that and there hasn't been a new firmware release for over 2 years now (I doubt there will be any future updates either). So FM works better for me on DMR simplex but I've not had problems with DMR Repeater/NXDN4800 or NXDN9600 on NFM.

Ubbe: are you possibly confusing DMR simplex on 12.5khz bandwith operating on a channel with 6.25khz steps? I've seen lots of that in Europe. But I'm really not sure how any DMR receiver designed/built for 12.5Khz BW reception would be able to decode a signal at half that BW without serious modification. AFAIK DMR can only achieve 6.25e (ie 6.25khz equivalence) but not 6.25khz actual like NXDN4800: it does this via DCDM - 2 separate channels - but still relies on a 12.5khz bandwidth to do so.

 

[Ubbe]

Ubbe: are you possibly confusing DMR simplex on 12.5khz bandwith operating on a channel with 6.25khz steps?

I don't think so. DMR uses 12,5 KHz modulation bandwidth as standard and the ships with SFM DMR sounds at about half the volume when listening in analog to the data modulation. They are using duplex repeaters and not simplex.

Most of the DMR systems in my area use a bandplan that has 12,5KHz channel steps with a 6,25KHz offset that would make it start at 420,00625MHz and next channel at 420,01875MHz and then continues with 12,5KHz steps.

dPMR are using 6,25KHz bandwidth and Whistlers TRX-2 decodes that and also show the mode on the display but Uniden scanners doesn't react to it, but I'm not sure if Uniden scanner even handles that digital format.

Also when there are 6,25 NXDN or IDAS a Uniden scanner struggles with that when the modulation and demodulated audio levels are so low. Uniden really needs to add a SFM mode to their modulation types that increases the audio level in the DSP.

/Ubbe

 

[racingfan360]

Ubbe: I'd appreciate a raw (discriminator) sample of this to look at: to date I've found no reference to any 'DMR super narrow modulation' system at all.

None of the Whistler TRX models decode dPMR either AFAIK, just P25/DMR/NXDN: Only the Icom R30 and AORs.

 

[jonwienke]

@Ubbe IMO you're confusing 6.25 KHz dPMR with non-spec DMR, or else your subjective listening to analog audio test is simply inaccurate. If there was such a thing as 6.25 KHz DMR there would have to be a specification for it somewhere.

 

[KevinC]

I don't think so. DMR uses 12,5 KHz modulation bandwidth as standard and the ships with SFM DMR sounds at about half the volume when listening in analog to the data modulation. They are using duplex repeaters and not simplex.

Most of the DMR systems in my area use a bandplan that has 12,5KHz channel steps with a 6,25KHz offset that would make it start at 420,00625MHz and next channel at 420,01875MHz and then continues with 12,5KHz steps.

dPMR are using 6,25KHz bandwidth and Whistlers TRX-2 decodes that and also show the mode on the display but Uniden scanners doesn't react to it, but I'm not sure if Uniden scanner even handles that digital format.

Also when there are 6,25 NXDN or IDAS a Uniden scanner struggles with that when the modulation and demodulated audio levels are so low. Uniden really needs to add a SFM mode to their modulation types that increases the audio level in the DSP.

/Ubbe

I didn't know any Whistler decoded dPMR?

 

[Ubbe]

your subjective listening to analog audio test is simply inaccurate...

Not subjective, the difference in audio level shows in the modulation window and in DSDplus source audio window.

I guess that they have just changed the modulation level and not the protocol.
If I take the discriminator audio from a TRX-2 and feed DSDPlus I can adjust the level until it decodes and it shows as standard DMR CAP+ so no different from the standard modulated systems.

Ships can use an international frequency band of 2x100KHz in 457MHz and 467MHz that I suppose has some very low nominal license fee but not as high as for a frequency that you apply for and gets assigned to you. Some cruising ships with 4 or more DMR frequencies seem to always be using those super narrow modulated systems, probably to fit inside the frequency range but not using adjacent channels that could interfere with each other in a receiver. But there have also been 2 frequency systems, but could have been that it was low activity and the other frequencies didn't announced themself when they where unused.

There hasn't been any crusing ships that has visited stockholm this covid-19 year. Each year there seems to be additional DMR systems being installed in ships that used to have analog subtone radios and probably some of them will use that low modulated DMR signalling. So those systems will become more common.

/Ubbe